 So, in the last three lectures, we have been looking at the issue of spintronic materials and what makes inorganic solids more attractive mainly because in the presence and absence of magnetic field, you see large changes in the resistance. And to give a classic example, we have discussed about manganate chemistry and how in a simple lattice, you have ferromagnetic structures which can be fine tuned to alter the electronic properties. In other words, we see a large change in the resistance by the influence of magnetic field which brings about a huge drop in resistance which we call it as colossal magneto resistance. Also in metallic samples, we have discussed how the interfaces can help in ordering ferromagnetic compounds in both ferromagnetic way and in anti-ferromagnetic way and thereby affecting the electronic properties. Another group of compounds have attracted interest and this is also under the broader area of spin electronics and this is called as dilute magnetic semiconductors. We all know that semiconductor industry is mainly governed by silicon technology and there are lot of additions to silicon technology which has come up in the last two, three decades. Therefore, in semiconductor industry, can there be anything new that can come out other than the existing silicon based technology. The most prominently used material other than silicon is gallium arsenide, but it is a very expensive technology because you cannot accommodate any amount of oxygen as a impurity. Therefore, this technology is a very, very touchy or very sensitive technology. So, mostly the semiconductor technology involves high vacuum and in conditions which is normally not exercised for other compounds that are used in functional applications. So if we can bring about a magnetic signature in a typical semiconductor, will that affect the semiconductor technology is the question. Today I am going to take you through some course of slides where I am going to show you specific examples where compounds which were originally thought to be semiconducting. If it is transformed to a magnetic semiconductor or if we can induce semiconducting property, what are the implications and how we can understand that and also I will give some examples of slightly higher band gap materials other than the typical semiconductors and show how magnetic properties can be governed and studied in those. Now to quickly take you through some of the basic definitions and then some examples which will form the case for today's lecture, let me ask this question. What are these dilute magnetic semiconductors? These semiconductors they make use of both charge and spin of electrons and thereby magnetic elements can be introduced to bring about a situation where a semiconductor which is non-magnetic can become magnetic semiconductor. So precisely this cartoon will tell us what such a situation is. This is a typical non-magnetic semiconductor where the semiconductor material is arranged in a periodic lattice and suppose I am going to add some transition metal ions into this semiconductor then one can see that this sort of magnetic impurities can be accommodated in the crystal lattice and they are in fact ordered and in such situation you end up with paramagnetic dilute magnetic semiconductors because these ions are magnetic but they are oriented in different fashion. Now what is important is the crystal lattice still remains the same, we are not disturbing the lattice and classic example is that of a 2, 6 semiconductor, some of the known ones are gallium arsenide and this is a typical magnetic semiconductor which is gadolinium sulphide but the most prevalent one is gallium arsenide. Now if the same paramagnetic DMS compound we can try to induce some holes and if we can induce some holes here in this structure those holes will actually turn this paramagnetic signatures to a concerted ferromagnetic signal. Thereby we translate a paramagnetic dilute magnetic semiconductor to a ferromagnetic dilute magnetic semiconductor. So two issues are there take a semiconductor and transition metal ions and if you can engineer some holes if you can add some holes and those holes will stabilize the paramagnetic stuff to a ferromagnetic stuff. So in essence you will see a concerted magnetic moment or a total magnetic moment which is prevalent even at room temperature. So this is a example of a dilute magnetic semiconductor it was reported by Ono and co-workers in Science magazine in 1998. Now questions that remain to be answered here is if manganese is doped in gallium arsenide in which the magnetic domain dopant provides a magnetic moment then a spin polarized charge also comes into picture because the carrier is now having a spin memory and this can actually bring about a new phase of spin tronic materials. So a transition metal ion doped in a semiconductor matrix will induce a magnetic moment and thereby provide a spin polarized charge carrier which brings about a spin tronic material. But there are some primary questions that we need to address what is this question what are the states of manganese what is the oxidation state are the manganese states localized or they are strongly hybridized with the gallium arsenide valence band it can stand aloof or it can actually hybridize with the gallium arsenide valence band and otherwise they can form a separate impurity band if they form a separate impurity band then you cannot call this as a dilute magnetic semiconductor it has to mingle itself with the valence band of the host material therefore it is very important to understand where this manganese is going because you are trying to doped to the tune of 2 percent to 4 percent not more than that because it has to be dilute. Now in such concentration where is your manganese and what is the nature of this manganese is the question. Now to understand this sophisticated techniques such as x ray absorption spectroscopy and x m c d that is x ray magnetic circular dichroism these are some of the refined techniques that are used to see whether it is truly a magnetic signal or not or whether it is coming from a impurity induced magnetic signature. So these two are synchrotron based analysis which can give you precise idea about what is the nature of the interactions in this compound. This cartoon will tell us what exactly the signature of manganese gallium arsenide is in the top figure we see the manganese l 2 3 h of the absorption spectra this is from the x ray absorption spectra. Now you can actually make this compound which is manganese doped gallium arsenide and you can look at the manganese l 2 3 h and you can do that in two ways one is magnetization in the you can actually try to probe this in two different directions one is parallel and anti-parallel alignment of polarization and when the magnetization is aligned in 001 that is this curve and the magnetization when it is aligned in 111 direction that is in this curve green curve. So if you clearly see that in two directions 001 and in 111 direction you see that there is a huge drop in the intensity. In other words the features x ray absorption features are radically different when you try to take the x ray absorption spectra of the manganese feature and in the plane of magnetization out of plane of magnetization as a result what happens you can clearly see that it is magnetized the lattice is magnetic as a result there is change in the x ray absorption structural feature. So this is one signature that can tell us that it is truly magnetic suppose manganese is not doped then you would see both the intensities in 001 and 110 they will be actually the same. So this is one signature in the other one you can see x m c d x ray magnetic circular dichroism for magnetization along 001 that is black here and the one in green is in the 111 plane the pronounced differences between the absorption spectra and the observed anisotropy in the features in the x m c d are most remarkable. You can clearly see in this region that the intensity of the features in both 001 and 111 plane clearly shows that there is a remarkable change in the x m c d and this work was actually reported by Edmonds and co-workers which is also published in PRL in the year 2006. Now if you make the x m c d if you take the x m c d and try to make a plot against the angular rotation then you can see the dependence of x m c d signal for the out of plane and in plane as a function of angle theta and you can clearly see that the open circles which represents the angular dependence in 110 plane and the solid symbols indicate the results in 100 plane. So, in the 100 plane you do not you see between here and here there is a angle of rotation which means there is a magnetic signature which is intrinsic of the manganese doped gallium arsenide and the same is true if you look at look at the x m c d features here the hall measurements clearly show that there is a change in the hall mobility or the whole density as we as we take the signature from the x m c d results. What does this mean? There is a angle dependent x ray magnetic circular dichroism which clearly shows that when manganese is doped in gallium arsenide there is a definite magnetic signature coming. Now, so what do we understand about this dilute magnetic semiconductors? These are semiconductors that are doped with magnetic ions the interaction among these spins lead to a magnetic state the charge of the electron enables semiconductors to process information and the spin allows to realize magnetic information for storage devices. These type of these type of materials have a lattice structure similar to that of undoped semiconductor. So, one of the main thing that one would require or one would look for is the single phase x ray single phase that has to be present not only x ray single phase it should be also magnetically a single phase material because you are dealing with the very small doping and in such situations you may not be able to trace the impurity ion in from the x ray because it is very low therefore, you need to know whether it is magnetically a single phase and structurally a single phase. There are several examples that can suggest how tricky this situation can become, but before that what one slide I would like to show what is the implication of this dilute magnetic semiconductor the possible application is it would create a revolutionary new class of electronic based on the spin degree of freedom of the electron in addition to the charge. So, so far the semiconductor devices they are more concerned with the charge of the electron. Now, if you bring about a spin ferromagnetic spin into this then you can actually translate this into a single integration on a single chip which will comprise of both the semi conducting property and the magnetic property and therefore, you can bring about a new possibilities in spin tronics. This was reported by Zutick in review of modern physics in 2004 for a better understanding on all the possible applications of this. Now, another question that we can ask about the usefulness of this spin and charge in dilute magnetic semiconductors when will this finally be as easy as switching on the light is it a near possibility or a distant reality that one can hope for many people keep asking this question and whether this can be ably applied to our computer technology in these days and specially because this can affect the random access memory this has a direct implication the answer that we can say as of now based on the results that we have that using this spin and charge in semiconductor industry is not too far. So, why there is such a great interest in these materials because in year 2000 detail and coworkers they reported using theoretical predictions they ran through several of the semi conducting materials and they tried to predict if there is a possibility of looking for new materials. In such case you start first with silicon which is our reference point compared to silicon you have two four semiconductors or two three five semiconductors or two six semiconductors you can see aluminum phosphide aluminum arsenide gallium phosphide gallium arsenide indium phosphide indium arsenide all these combinations are somewhere close to silicon these are the theoretical predictions indicating that they can turn ferromagnetic. Now notably if you see we are somewhere around this region of room temperature if we have to realize a room temperature ferromagnetic situation then two compounds really cross this line and those are gallium nitride and another one is astonishingly zinc oxide though both these compounds are known to be ferromagnetic or it is calculated at to show that they possess a definite magnetic movement beyond room temperature. Therefore, the target molecules or the target compounds which which have been studied in the recent past or the substituted gallium nitride materials and also zinc oxide there are other ones based on zinc compounds which are the zinc chalcogenites namely telluride and selenide they also show magnetic property, but nevertheless the ones which are around the room temperature carries our attention. Therefore, I will try to show in the next few slides the some of the research that has gone into several of these oxides or non oxide based compounds and we will try to understand how we can clearly escape from the situation where we realize a impurity induced ferromagnetic compound and we will also try to see what are all the characterization facilities that are available for us to go into microscopic details to find out whether they are truly magnetic signatures or they are impurity induced ones. To start with let me show an example of zoo and co-workers who reported this compound nickel doped titanium and this was reported in APL in 2006. You can see here they have formed using ion implantation technique they have tried to dope nickel in titanium matrix and this is the T M picture which clearly shows that this is a amorphous titanium matrix because you can see there is no order there and in this there are submerged nickel clusters or nickel particles and these are of the order of say 6 nanometer or so roughly there are 6 nanometer nickel particles which are actually embedded in titanium matrix. In such case what will happen you will see the magnetic signature very clearly you see a signature at 300 K and this should have actually blown up but what you see here even at 10 K you do not see a very clear change in the hysteresis but a very feeble hysteresis is developing at low temperature. This was the first report on nickel doped TiO2 and in this case you can see that nickel seems to be in the nickel zero state as a nickel metallic cluster it is not a nickel substituted in TiO2. There was another example that was reported by Matsumoto in 2001 and what did they do they have doped cobalt in TiO2 because TiO2 is also a band gap material wide gap band gap material and if you clearly look at the XRD pattern of 8 percent cobalt doped in TiO2 you can clearly see the peaks of annites TiO2 only with no impurity peaks. So if you look at the cobalt signature you would see that it is epitaxially growing and there is no signature and there is no signature of cobalt crystallizing out in any other form. So in that case you can look at the higher resolution Tm also we do not seemingly see any sort of change in the interface. It is nicely growing on LiAlO3 substrate but nevertheless we do not have any clear idea where these magnetic signal is coming from. If you look at the magnetic signature m versus h plot clearly shows at room temperature for a 7 percent cobalt doped one you clearly see this hysteresis look coming and if you are going to sweep the m versus T plot for the same 7 percent cobalt doped TiO2 you can clearly see that there is ferromagnetic transition is beyond room temperature. So just for 7 percent cobalt doped in TiO2 you see the Tc is above room temperature and there is no signal of any cobalt crystallizing out. If you look at this cobalt doped zinc oxide for a change you would see the XPS that is X-ray photoelectron spectroscopy results which was reported in a series of sample. If you look at the cobalt 2 p 3 by 2 and cobalt 2 p half you see a XPS feature which is with very fine features you would be tempted to say is that cobalt is nicely doped in zinc oxide but if you carefully look at the signature you would find for a 4.8 nanometer sputtered film. If you deconvolute these features and if you deconvolute these features you would find that cobalt 2 place is definitely there which means it is clearly substituted in ZnO this is zinc oxide and you would also see the cobalt 2 plus satellite features here these are the satellite features. Now along with that you also see a clear feature coming for CO which is metallic. In other words you have apart from cobalt getting doped in the ZnO you also have a proportion of cobalt which is staying as a metallic cluster. So in this case what you would clearly understand is the magnetic signature although it can come from substituted cobalt which can be doped in the valence band region of your zinc oxide lattice there is a clear possibility of metallic cobalt contributing to the magnetic property. So this is very important and we need to be extremely careful that the magnetic signatures what we observe is actually coming from the doped situation and not from the metallic clusters. If you take for example another high band gap material like HfO2 which is doped with nickel and this can be achieved by pulse laser deposition technique you would see that the magnetic moment for the YSZ that is the substrate. Substrate is almost showing a very very weak magnetic moment of the order of 10 power minus 5 emu and if you doped if you take the raw data of the nickel doped one you see there is a remarkable jump in the feature and if you try to subtract the background then you can see the film is actually contributing something like this. Now between the substrate and the nickel doped sample the difference is only in this value nevertheless it is a very small feature and therefore you need to look at the m versus H feature you can see that in the parallel and perpendicular geometry there is a change if in parallel and perpendicular there is a change then we can say that nickel is doped inside HfO2 therefore you can say that the ferromagnetism is originating from the doped matrix rather than from any type of clusters this was reported by Hong co-workers in 2005 in APL. Cobalt doped HfO2 this also can be prepared from Paul's laser deposition you can clearly see that this is clearly a doped situation because if you look at the x-ray of the thin film which is deposited in YSZ these are the YSZ x-ray features and along with that comes the reflection for HfO2 this peak is for HfO2 and this peak is also for HfO2 which is 002 and 004 features they nicely grow on YSZ film. Now if you look carefully at this deviation if you look carefully at this peak now you would find out that between the doped and the undoped this is the cobalt doped and this is the undoped there is a clear deviation in the x-ray pattern showing that when you doped cobalt then there is a shift which means cobalt is substituted in HfO2 matrix as a result whatever magnetic feature that is coming whether it is 3 percent or 4 percent or 5 percent you see a systematic increase in the moment of this cobalt doped HfO2 compound. So one can say that there is a possibility of doping this material in HfO2 but we need to also understand where this magnetic signatures are coming it is proved that the ferromagnetism is attributed to formation of a cobalt rich surface layer because if you do the yields as a function of the thickness of your HfO2. So you have your YSZ here YSZ substrate and if you have your HfO2 thin film and if you keep on doing the yields study across this thickness as you go towards the surface of this layer as you go to this surface you see the cobalt magnitude or the amount of cobalt is actually increasing the intensity of the cobalt peak is increasing as you go towards the surface of the HfO2 peak therefore it was concluded that it is not purely a dilute magnetic semiconductor rather it is coming from a rich cobalt surface layer which is contributing towards the magnetic property. If you take another example this is another classic example of a wide band gap material MGO which is having a band gap above 4 electron volt and in this case if you are going to dope nickel then you can see that there is a paramagnetic signal which is superimposed on the ferromagnetic signal mainly because this is seen at 300 K and this is seen at low temperature substitution as well as presence of nickel clusters lead to ferromagnetism at room temperature. So, at the macroscopic level if you look at the magnetic feature it looks as though you have a very strong ferromagnetic signature but if you clearly probe it these are especially at low temperatures you could see that there is a paramagnetic signature which is coupled with a ferromagnetic signature and this was reported by Raman Chintren in 2007 and if that is the case then if you make a plot of magnetization versus temperature you would see if there is a sudden upsurge in the magnetic movement at low temperatures then the indication is this is due to substitution and the paramagnetic behavior in the case of substitution comes at low temperature. So, with all these confusions around we do not know whether the magnetic signature in this sort of wide range of semiconductors that have been studied whether the whether the magnetic information that we are getting is truly coming from a doped semiconductor or it is coming from a impurity induced magnetic property. If it is impure induced then it is of no use for the spintronic property therefore we need to be extra careful to know whether the magnetic information is a true phenomena or it is a impurity induced phenomena because in the past it has been observed when you are doing magnetic study even if you are going to pick up these materials with a nickel spatula or iron spatula or iron forceps even those small impurities can induce quite lot of signature specially because the sort of magnetic signal that you are seeing in a thin film situation is of the order of 10 power minus 5 emu you have to be very very careful where this signatures are coming from. So, to elucidate this it is possible for us to study a different sort of compounds to say what could happen if there if it is a transition metal cluster induced ferromagnetism and what would be the signature if it is truly a ferromagnetic situation. So, for this reason we can actually try to induce magnetism in white band gap oxides by doping transition metals we can try to do that by doping nickel cobalt iron in ceramic oxides like zirconia, siria and alumina. I may not be able to run through all these examples but I will certainly try in the next few slides to show you what will happen if you have nickel cobalt and iron doped in zirconia and try to understand what is the magnetic signature that we can look for if you try to dope it in a white band gap material. In fact, zirconia is not just a semiconductor we can classify this even as insulator because the band gap is more than 5 ev and we can try to see if we can achieve room temperature ferromagnetism in this high-key dielectric ceramic oxides and we can see whether this can be used for potential applications in spin tonic technology. Now, why we are choosing nickel cobalt and iron based zrO2 because they form a very important class of compounds called cermets. A cermet is nothing but a ceramic and a metal composite which is known for more than 3 decades now and these are used for mechanical applications because zirconia when it is doped with any transition metal it improves the mechanical strength by orders. Therefore, intentionally people dope this transition metals including molybdenum people have used it and this comes under a special category called cermets. So, cermets are nothing but ceramic metal composites and the optimal properties that you can achieve is one is it is a ceramic. So, you have high temperature resistance and one is you have a metal you have the ability to go through plastic deformation. So, plugged in you have 2 in 1 where a metal is actually interspersed in a ceramic metal which will add strength to the material. But we are going to use such a cermet composition to study the magnetic information in this oxides. The metallic elements used as I told you are nickel molybdenum and cobalt cermets can also be made with a concentration of 20 percent metal by volume and cermets are used in the manufacture of resistors capacitors and other electronic components which may experience high temperature. So, these are the fundamental use of the cermets, but what we are going to do is use this cermet class compounds to see whether we can understand little bit on the magnetic signature. So, how do we do this because zirconia is a material which is a high temperature material. Therefore, you need very high temperatures to prepare this compounds. We are going to show how using wet chemical routes one can prepare this oxides and there is no need even to make thin films using costly methods like PLD or MB. These materials can be prepared at a very faster rate and we can achieve even high temperature phases by non-conventional routes. I will show one or two examples of how using microwave combustion route we can prepare this compounds. Microwave assisted combustion route can form a very useful route to prepare this sort of high temperature oxides and in the module 1 on wet chemical routes I have already discussed with you the use of microwave combustion. The main advantage of microwave combustion is you try to generate high temperatures from within the sample instead of supplying heat to the sample. So, this is the conventional electro heating method whereas this is the microwave heating method and the reason why we can use microwave is you are actually starting with some material which is made of nitrate and fuel which is urea and these are materials which have very high dielectric constant. Therefore, they absorb the microwave much more easily due to a mechanism called dipolar polarization. As a result, you can initiate combustion reactions within the sample which can easily lead to a one step decomposition straight to metal oxide. Therefore, if you have to prepare zirconia at even 1200 degree C, you can achieve that using just a microwave. In other words, a furnace less technique can be used to initiate high temperature reactions where you can make metal oxide. So, let us say that metal oxides are made out of this reaction then we need to look at the purity and then we need to look at the magnetic signature that we are going to see in this compound. So, we will first start with nickel doped zirconia powders and try to see if we use combustion synthesis to prepare what are the magnetic signatures in this and this is just the ritual analysis for 1 percent and 4 percent doped compounds. You can see clearly that the X-ray pattern that we see for 4 percent nickel doped and 1 percent nickel doped samples clearly show that the X-ray pattern resembles that of cubic zirconia. If it is going to be monoclinic which is another phase which is reported to be stable at room temperature then you would see signature of the monoclinic phases coming somewhere here, but one would clearly see that there are no features of monoclinic peaks present in the samples clearly showing that just using a simple technique one can prepare cubic zirconia. Now, we do not have to just limit with 1 percent and 4 percent which is of interest for our DMS study one can even go to 10 percent or 20 and we can go even up to 60 percent and try to see in the Cermet compositions where exactly nickel oxide impurity peak is coming as you see here 10 percent peak we do not we still see zirconia in cubic phase and if you go to 20 percent 30 40 you do not see any trace of monoclinic phase coming here. So, this is still in cubic but what you would see here above 40 percent small peaks are coming these are the nickel oxide peaks. So, this nickel oxide peaks are have started coming beyond 40 percent therefore, if we need to look at the magnetic phases one can say that safely up to 30 40 percent we can keep looking at this magnetic signatures carefully and try to understand whether they are impurity induced or they are coming from substituted ferromagnetism. You can see in the first view graph of this magnetic signature for a 1 percent nickel doped zirconia very clearly there is a hysteresis loop emerging at 300 k and at 4.2 k. Now to make sure that this is not coming from zirconia itself because zirconia is actually a oxygen scavenger. In other words it can easily form Z r 2 minus delta r plus delta because zirconia takes carries a electron and it can give electron and as a result it is also known as fast ion conductor. But what is important here is any amount of excess oxygen is present it can easily go into the Z r 2 lattice. So, if we should make sure that the magnetic signature is not exactly coming from oxygen star symmetry. So, if you look at the parent compound parent compound clearly shows a negative trend in the m versus h curve showing that it is non magnetic. So, any signature that is coming is actually coming from nickel doping only. So, for 1 percent nickel doping you can clearly see it is showing a room temperature ferromagnetism and if it is a room temperature ferromagnetic system then one would typically see that the coercivity value is increasing and the moment is increasing if we measure it at 4.2 k. But what we see here is more of a paramagnetic signature which is coming like this for 4.2 k indicating there is a paramagnetic component associated with the ferromagnetic impurity at 1 percent nickel doping and you can see this is clearly blown to show how the coercivity is varying with the temperature. So, definitely there is some possibility of inducing ferromagnetism at this stage. Now, if you go to 4 point for 4 percent nickel doping you can see that it is not showing any more of the paramagnetic signature at 4.2 k and there is a definite change in the hysteresis and hysteresis loop clearly shows that there is a strong ferromagnetism that is induced into this Zirconia matrix and just to make sure that we are still playing in the safe domain you see that the Z r O 2 which is undoped is showing a negative magnetization slope. Therefore, whatever is seen here is actually coming from nickel doping. So, you can actually run through from 1 percent you can go up to 60 percent of nickel and try to see what is happening you can see that the M S value is actually increasing up to 50 percent and beyond 50 percent suddenly you see the magnetization is decreasing why it is happening we I have already shown that beyond 40 percent nickel oxide starts precipitating out and we can try we can based on the magnetic signature then you can try to look at the Bohr magneton in terms of formula unit in terms of nickel atom you can see that there is a progressive increase in this case and then it falls back and then again it increases therefore, there are some safe domains where we can we can look for magnetism that is truly coming from nickel doping and there are some domains where it is coming from the segregated phases we can see that from this sum up of results 1 and 4 percent clearly shows a ferromagnetic group at room temperature this we have seen and if you increase the nickel concentration you can clearly see that the magnetization is systematically increasing but for 60 percent suddenly it is dropping down. So, that means nickel keeps on going but if you make a plot of magnetization as a function of nickel concentration you would see that there is a region where the slope is only marginal or we can say it is linear here may be even up to this place and then suddenly the linearity goes this way and then it drops down. So, we can actually say that there are three regions in nickel doping as a function of magnetization a region from say 0 to may be 10 percent is one region and beyond 10 percent you see a increase in the magnetization and then it again falls down. So, we can sort of propose a tentative magnetic phase diagram saying that if at all we are looking for a dilute magnetic semiconductor then this is the region which we can look for where it is safely nickel which is clearly substituted into the Z R O 2 matrix and beyond that in this is a Cermet region where nickel is actually precipitating out as nickel clusters and those clusters are embedded in Z R O 2 matrix as a result you clearly see with more and more of nickel nickel coming out as nickel metallic nickel there is a increase in the magnetization. So, if you look at this magnetic phase diagram we can clearly say that if we are talking anywhere about a possibility of a dilute magnetic semiconductor situation then we should only be talking about 0 to less than 10 percent phase where you can clearly substitute nickel in Z R O 2 matrix. We can clearly see that from the T M pictures also this is for one percent nickel one percent nickel what you would see here is a polycrystalline feature, but you do not see any sort of nickel or nickel oxide phase coming in one percent, but in four percent nickel you see a small feature of nickel oxide which is precipitating out this is clearly evident from the T M results. So, we can say that even between one to four percent there is a safe compositional limit where we have to restrict for a dilute magnetic semiconductor and if you go further your T M clearly shows that for fifty and sixty percent there is a clear signature of nickel oxide that is coming out and these particles for example, if you map it these are supposed to be nickel oxide which is actually showing this sort of nickel and nickel oxide features in the electron diffraction pattern. So, you have a increase in the magnetic moment, but the magnetic moment is essentially coming from nickel metal rather than nickel substitution and this we can see from the ferromagnetic resonance as well you can clearly see for one and four percent there is a systematic change in the magnetic resonance. Therefore, there is a clear possibility of a D M S that is in picture and how do we know in a macroscopic way we can even look at the powders the morphology of the powders the moment you dope nickel you can see zirconium particles totally the morphology transforms in a very different way when you dope even one or four percent of nickel and then these are the XPS studies XPS studies for one percent nickel clearly shows there is no satellite feature which means there is only one oxygen species there. Suppose there is Z R O 2 and then nickel oxide then both will actually show two different oxygen peaks. So, we can clearly say that there is only one phase and therefore, there is no asymmetry in the oxygen one is oxygen peak and here again if you see the nickel 2 P 3 by 2 and nickel 2 P 3 by 2 peaks for one and four percent of nickel there is no satellite features in the nickel 2 P. Therefore, we can clearly say that nickel is there only in one oxidation state which means nickel is in nickel 2 plus only same is true if we take cobalt case cobalt is another ferromagnetic ion which can be doped as you can clearly see whether it is one percent two percent or four percent it is absolutely a clean Z R O 2 cubic phase and you do not see any sort of impurity that is induced here and you can also see the magnetic moment is increasing as a function of cobalt therefore, there is a clear possibility of a DMS phase that is emerging out against a undoped situation. Therefore, even cobalt seems to throw a possibility for a clear dilute magnetic semiconductor situation and as I told you earlier the cobalt substitution can be pronounced in the morphology compared to Z R O 2 you can see that cobalt is literally changing the morphology and if you keep substituting cobalt to higher percentage even up to 60 percent unlike the nickel case you can see here that you have a clean zirconia phase that is coming, but beyond 40 percent you can see that cobalt oxide phase that is C O O is coming and it is becoming more prominent and when you substitute for 60 percent the system instead of increasing in crystallinity you can see as you keep doping cobalt the crystallinity dampens and then you almost get a amorphous phase. So, cobalt seems to be getting substituted in the zirconia lattice and there is no signature of C O 3 4 which is a magnetic phase which is present anywhere in the x-ray therefore, we can say that the magnetic signature if at all anything is there it is not coming from any of the oxide impurity of cobalt it is actually coming from a doped situation and this is the similar thing you know you can also try to sinter the same powders at a higher temperature to see whether x-ray is altering you do not see systematically any change with the sintering conditions and you can also see that the lattice parameters by and large remains the same whether it is a as prepared sample or sintered sample saying that the oxidation state of cobalt does not seem to vary with annealing in other words it says that cobalt is not just embedded in the matrix, but it is actually substituted and you can also see from these two cartons whether it is as prepared samples or whether it is sintered at 400 degree C you can see the clear trend in the magnetic property initially it is low and then it picks up just like the way we saw in nickel there is a increase up to 40-50 percent and then there is a drop drop is actually coming from this drop in a moment is coming from impurities of cobalt oxide. So, what we can see from this cobalt substituted compounds beyond the 10 percent you can see that the ferromagnetic signature shows that if you sweep magnetization as a function of temperature they all show a steady temperature independent variation showing that the T c is above 300 K in all these compositions. So, these signatures may come from cobalt clusters whereas, dms phase is possible less in less than 5 percent cobalt doping. So, we can see this trend even as we sweep through this I have already shown you the phase diagram and if you can see the T m features even up to 1 10 percent sorry even up to 10 percent of cobalt doping you would see there is no signature of cobalt oxide coming it is a clean Z r O 2 phase which means cobalt is substituted and once you go beyond that you can see the cobalt phase is coming. So, I will quickly go through the last example to show what exactly we can conclude out of doping magnetic property in this Z r O 2 matrix let us take the example of iron. Now, if you dope iron carefully only in low concentration limits say up to 9 percent 3 6 and 9 percent you can clearly see it is again showing clean Z r O 2 cubic phase. Now, once you look at the magnetic property you see that the magnetization is steadily increasing, but the clue whether it is really coming from doped situation or from any other impurity comes from mass bar. You can see for example here in this case it is actually 3 percent this is 6 percent and this is 9 percent this is at 77 Kelvin and this is at room temperature one would clearly see that for 3 percent you only see the doublet here you only see the doublet in this case whereas, when you go to 6 percent you can see that this doublet is getting split into a sextet and more so in 9 percent and similar feature is seen even in the 77 Kelvin recorded mass per peak what we can say is if there is a doublet then iron is actually isolated there is no iron-ion interaction in this case whereas, in the case of 6 and 9 percent we seemingly find Fe 3 O 4 impurities which are creeping up that is why for 6 and 9 percent you can see a sextet feature is coming for the iron. So, safely we can say what is the compositional limit that we can look for again you see for 3 percent or 6 percent and 9 percent radically the morphology is changing. So, what we see for nickel cobalt and iron we can say that less than 3 percent of this transition metals doped in zirconia there is a clear possibility of a dilute magnetic signature that is coming beyond that even though there is a steady or there is a schematic trend present in the magnetic behavior one has to be careful that this is not actually the true signature that comes from a dilute magnetic phase rather it comes from a impurity induced phase. So, we can sort of say from this study that there is a possibility for a dilute magnetic semiconductor not only in z n o type of compounds even in high band gap materials, but we need to be very cautious about finding what is the limiting concentration at which this magnetic phase can be found out. So, with this I conclude and we can look into this aspect later. So, make some quick analysis the analysis of magnetization data suggest that iron induces room temperature ferromagnetism high temperature phase. Mass power study of 3 percent shows doublet and the corresponding 6 and 9 percent show superimposed sextet and doublets the isomer shift and quadrupole moment indicate iron to be in the 3 oxidation state to occupy different octahedral sites associated with some amount of disorder. So, in cases where we do not have a clue here is one classical example that we can use mass power study to elucidate what is the limiting compensation at which we can realize dilute magnetic phase I stop here and we will continue in the next lecture.