Magnetic Properties and Oxygen Defects of Dilute Metal Doped Tin Oxide Based Semiconductor

Chemical and magnetic states of iron doped tin oxide (SnO2) as a diluted magnetic semiconductor (DMS) at room temperature have been investigated using 57Fe Mössbauer spectrometry, XRD and magnetometery. The influence of the doping conditions of SnO2 with iron on the generation of oxygen defects was reviewed and discussed on the basis of ab initio calculations. The magnetic properties depended on preparation conditions, such as thermal decomposition and sol-gel processing as well as 57Fe and super-dilute 57Mn implantation. It was shown that Sb codoping in Fe doped SnO2 increases the saturation magnetization. Doping of Fe(Sb)-SnO2 with nonmagnetic Zn ions up to 7 % also increases the magnetization although there is no precipitation of crystalline magnetic phases. The codoping of two transition metal ions (Fe-Co, Fe-Mn, Fe-Ni and Fe-V) in SnO2 matrix enhanced the magnetization as compared with that of single metal ion doped samples. It is suggested from different valence states of doped metal ions that double exchange interactions occur through or near the oxygen vacancies in SnO2. The SnO2 doped with dilute 57Fe may show the intrinsic and/or extrinsic DMS properties. Oxygen vacancies play an important role in the intrinsic DMS. The intrinsic nature of DMS is supported by both, experimental results and ab initio calculations. The long range interactions between diluted magnetic ions are considered to occur through electrons produced by oxygen vacancies or electrons induced by Sb5+ doping.


INTRODUCTION
XIDE diluted magnetic semiconductors (DMSs), which possess good semiconducting and magnetic properties at room temperature (RT), are promising materials for spintronic devices.Magnetic alloy semiconductors (II-VI, III-V) such as Mn doped ZnTe, GaAs and InAs, which show ferromagnetism at low temperatures, have already been utilized as spintronic devices. [1]The first oxide DMS system was reported by Matsumoto et al. (2001).The authors showed that Co doped TiO2 films prepared by laser ablation show ferromagnetism at RT. [2] T. Dietel et al. [3a] And Pearton et al. [3b] showed the relationship between band gap and Curie temperature of semiconductors. [3]In order to realize RT-DMS, the semiconductor with large band gap is profitable as candidate material. [3]Ogale et al. reported that transparent Co-doped SnO2 shows the high temperature ferromagnetism with a giant magnetic moment. [4]This seems to be due to precipitated magnetic compounds.SnO2 film with band gap of 3.6 eV is transparent and electrically conductive.SnO2 doped with metal ions has been used for a gas sensor working at temperatures of several hundred degrees Celsius. [5]here remain the questions why the magnetic moment in oxide semiconductors increases by doping them with small amounts of magnetic ions, and why the DMSs show high Curie temperature.The study of the magnetism in diluted magnetic oxides became an interesting issue over the last decade. [6]Coey et al. reported the magnetic polaron models and the charge transfer band models with impurity band as dilute magnetic mechanism. [7]Which dilute magnetic oxide semiconductor is fact or fiction is discussed. [8]It is necessary to reveal the chemical and magnetic states of doped metal ions in semiconductors and whether the doped metal ions exist as uniformly dispersed metal ions, clusters and/or precipitated compounds.
O 57 Fe Mössbauer spectrometry provides the information of electronic and magnetic states of iron nanomaterials.Conversion electron Mössbauer spectrometry and X-ray Mössbauer spectrometry (CEMS and XMS) can be used for characterization of iron included in solid surface and thin layers. [9]The vibration density states (VDOS) of oxides containing Mössbauer nuclei can be characterized by another Mössbauer technique, the nuclear resonance inelastic scattering (NIS) using synchrotron radiation. [10]hus, the valence states, magnetic states, and local VDOS of Fe doped oxide semiconductors can be clarified by using Mössbauer techniques of ca. 1 % 57 Fe probes.
Various transparent DMS films have been characterized by 57 Fe CEMS.For example, transparent 6 % 57 Fe doped TiO2 film, prepared by laser ablation in vacuum of 1.33 × 10 -6 Pa, shows Kerr effect (optical ferromagnetism) at RT.It was clarified by 57 Fe CEMS that the magnetic origin is mainly due to metallic Fe clusters. [11]n this review article, 57 Fe Mössbauer analytical results and magnetic properties of SnO2 based materials doped with diluted Fe ions are introduced together with theoretical results obtained by ab initio calculation for configurations of substituted Fe and oxygen defects of Fe doped SnO2. [12]GNETIC PROPERTIES OF Fe DOPED Sn OXIDE POWDER Fe Doped SnO2 [13] 10 at % Fe doped SnO2 powder was prepared by a sol-gel method and the thermal decomposition.The relationship between magnetization curves and annealing conditions is shown in Figure 1 (a).The ferromagnetic hysteresis including a paramagnetic component is observed.
The magnetic hysteresis depends on annealing temperatures.10 at % Fe doped SnO2 annealed at 600 °C shows the highest saturation magnetization.The magnetic relaxation peaks are observed in addition to paramagnetic doublets and a minor sextet of Fe2O3 in the Mössbauer spectrum.The sample annealed at 500 °C shows only two doublets of Fe 3+ although the saturation magnetization is larger than that of the sample annealed at 650 °C, which contains the weak magnetic component of Fe2O3.The doped Fe species are embedded in so large grains of matrix SnO2 that cannot show the superparamagnetism.s shown in Figure 2, the saturation magnetization (Ms) of the sample heated at 500 °C for 2 hours decreases by annealing at 500 °C further for 4 hours.The oxygen defects are considered to be repaired by annealing for long time.Therefore, the magnetization is related to oxygen defects induced at the initial annealing.Two doublets observed in Fig. 1 (b) are assigned to Fe 3+ (isomer shift (IS) = 0.34 mm s -1 , quadrupole splitting (QS) = 0.80 mm s -1 ) and Fe 3+ (IS = 0.28 mm s -1 , QS = 1.60 mm s -1 ).This suggests that high spin Fe 3+ ions interact as a long range ordering through electron spin localized at oxygen deficiency under the magnetic fields, that is defect induced ferromagnetism due to overlapped polarons as shown in Figure 3. [14] Sn 4+ O2 doped with Sb 5+ is n-type semiconductor, whereas SnO2 doped with Fe 3+ is p-type semiconductor.The ionic radii are 0.069 nm for Sn 4+ , 0.064 nm for Fe 3+ , and 0.060 nm for Sb 5+ , respectively.Doping Sb 5+ into SnO2 increases the electric conductivity and the solubility of Fe 3+ doped.The saturation magnetization of Sn0.8-yFe0.2SbyO2increases with the increase of Sb as shown in Figure 4. [14] However, the magnetization decreases by compensating the induced carrier density by holes formed when the doping rate of Sb becomes almost the same as that of Fe.

Sb and Fe Codoped SnO2
Mössbauer spectra of Sn0.8-yFe0.2SbyO2(y = 0.25) show major doublets and a minor magnetic sextet at RT.The magnetization is relatively large and the coercivity is small like soft magnetic behavior.When Mössbauer spectra are measured at low temperatures, the area intensity of doublets is relatively transferred into that of a broad sextet with the decrease of the measuring temperature as shown in Figure 5.The hyperfine fields are not so dependent on the measuring temperature.It is considered that the Effect of annealing at 500 °C on magnetization of 10 at % Fe doped SnO2. [13].
Figure 3. Diagram on the formation of polaron.Oxygen atoms are not displayed.▯: oxygen deficiency. [7]gure 4. Dependence of saturation magnetization on doping rate of Sb in 20 at % Fe doped SnO2. [14]gure 5. Mössbauer spectra of Sn0.55Fe0.2Sb0.25O2,measured at 10 K, 20 K, 40 K, and RT. [14]oublet peaks obtained at RT are not due to fine particles of iron oxides, but due to the small domain size, that is the spin-spin interaction.It is to note that a ferromagnetic behavior including a paramagnetic component is observed in the magnetic hysteresis curves although almost all samples show the doublets of paramagnetic Fe 3+ .The abnormal phenomena are considered due to the exchange coupling between local electron spin of Fe 3+ through the carrier electrons doped.The magnetic moment of Fe 3+ induces the polarization of carrier electrons, which interact with the next neighbor Fe 3+ .Thus, the possible mechanism is considered to be connected with the exchange interactions between iron ions and magnetic defects being mediated by impurity induced free charge carriers.
As compared with single Fe ion doped SnO2, Sb and Fe codoping into SnO2 results in enhancement of saturation magnetization without the precipitation of impurities.This suggests that the origin of ferromagnetism is mainly due to the increase of electron carrier density by doping Sb 5+ .
119 Sn Mössbauer Spectrum of Fe Doped SnO2 [15] 119 Sn is not a magnetic atom itself.However, the transition by gamma ray absorption occurs between the exited state of nuclear spin I = 3/2 and the ground state of I = 1/2.In 119 Sn Mössbauer spectra measured under the applied magnetic fields, the magnetic sextet is expected to appear like 57 Fe Mössbauer spectrum.When 119 Sn Mössbauer spectra of Sn0.8-yFe0.2SbyO2were measured under magnetic fields of 0.3 T and 0.55 T, the peak with broaden width was observed in 119 Sn Mössbauer spectra as shown in Figure 6.Thus, it is found that even 119 Sn nucleus in the bulk area is also sensitive to applied magnetic fields. [15] 119Sn can be used as one of magnetic probes for dilute magnetic materials.

Nonmagnetic Zn Doped
FexSbySn1-x-yO2-δ [16] XRD peaks of Zn doped FexSbySn1-x-yO2-δ show only the rutile structure of SnO2 even if doped with Zn up to 7 %, whereas the spinel, Zn2SnO4, is additionally observed for more than 10 % Zn doped samples.XRD peaks of Zn2SnO4 are almost similar to those of spinel ZnFe2O4.The Mössbauer spectra are composed of two paramagnetic doublets and magnetic relaxation peaks as shown in Figure 7.A doublet with small QS was assigned to Fe 3+ coordinated with six oxygen atoms and another doublet with large QS was assigned to Fe 3+ closed to oxygen vacancy.However, both doublets are due to Fe 3+ , which are located close to oxygen vacancies in different configurations as described later in section Magnetic moments and oxygen vacancies of Fe doped SnO2 by ab initio calculation.The area intensity of magnetic relaxation component and the saturation magnetization are plotted for doping rate of Zn, respectively, as shown in Figure 8.It is found that the saturation magnetization is correlated with magnetic relaxation component of Fe 3+ .When more than 10 % Zn is doped, the magnetic relaxation component disappears in the Mössbauer spectra, but the weak magnetization is remaining.It is considered due to magnetic defects produced at the interface between the precipitated impurity and SnO2 matrix.

SnO2 Codoped With Two Transition Metal Ions
In the case of single metal ion doped SnO2, it is known that the saturation magnetization increases with Fe concentration, but decreases with Co concentration.The codoping effect of Fe and Co doped SnO2 were studied. [17,18]The samples were prepared by a sol-gel method and a thermal decomposition at 550 °C.The crystallite size is about 20-40 nm in diameter.As shown in Figure 9, 1 % Fe and 0.5 % Co codoped SnO2 enhances the saturation magnetization (Ms).When more than 3 % Co are doped into Fe doped SnO2, the magnetization decreases.There is a possibility that ferrite is precipitated with increase of Co content, but the broad magnetic components as shown in Fig. 10 are absolutely different from that of CoFe2O4.It is hard to consider the precipitated ferrite as the origin of ferromagnetism.It is not sure whether a double exchange interaction of Fe and Co through Sn and O occur or not, but it was confirmed from Co L absorption edge in XAFS that 1 % Co ions have the mixed valence states of 2+ and 3+.It  SnO2. [17]gure 10. 57Fe Mössbauer spectra of SnO2 doped with 1 % Fe and (a) 0 %; (b) 0.5 %; (c) 2 %; and (d) 3 % Co. [17] Croat.Chem.Acta 2015, 88(4), 579-590 DOI: 10.5562/cca2784 is considered that the local electrons existing in oxygen deficiency and isolated Sn atoms are intermediates between ferromagnetic interactions.The magnetization properties of Mn and Fe codoped SnO2, and Fe and Ni codoped SnO2 are also studied. [19,20]ilute Fe-Mn codoped SnO2 is synthesized by a solgel method.The Fe-Mn codoping enhances the magnetization in comparison with the case of single metal ion doping.The Ms values are correlated with the crystallite sizes.Mössbauer spectrometry revealed the magnetic sextet and relaxation peaks, which suggest that Fe ions doped contribute to the magnetic ordering and super-paramagnetic properties.X-ray absorption spectroscopy revealed that Mn 3+ and Mn 2+ mixed states are dominant in Fe-Mn codoped SnO2. [19]n the case of Fe-Ni codoped SnO2, the following possibilities for the origins of RT ferromagnetism are considered.The formation of Fe and Ni complex oxides might become one of the candidates for ferromagnetic ordering, since Ni-based spinel-type ferrite is well known as a ferromagnetic material.However, the observed doping dependencies in Ms of Fe-Ni codoped SnO2 cannot be explained by the simple formation of secondary phases.It is therefore deduced that the Fe-Ni codoping enhances the Ms not by the segregation of secondary phases but by the exchange interaction. [20]n the case of Fe-V codoped SnO2, Fe-V codoping also enhanced the Ms, which showed the maximum Ms at 1 % V and 1 % Fe codoping.With further increase of Fe-V codoped into SnO2 host, the Ms decreased.Chemical states of vanadium ions were deduced as V 5+ states by XAS.Mössbauer spectrometry revealed that the intensity of sextet components is related to the Ms, which indicates that small amounts of Fe-V codoped are effective to enhance Ms. [21] It is to note that the sextet component is like hematite, which shows weak ferromagnetism at RT although the XRD peaks of hematite are not be detected.
As compared with single metal doped SnO2, the ferromagnetic exchange interaction is enhanced by codoping two transition metal ions.A codoping technique that employs different d electron numbers becomes essential for the stabilization of ferromagnetism with the control of both saturation magnetization (Ms) and the coercive field (Hc) at RT. [20] Fe ION IMPLANTED SnO2 FILM [ 2 2 ] SnO2 film implanted with57 Fe at RT did not show Kerr effect at all. 119Sn CEM spectra of SnO2 film implanted with 1 × 10 17 ions / cm 2 57 Fe are composed of two doublets of Sn 4+ (80 %) and Sn 2+ (20 %).By 57 Fe ion implantation, Sn 4+ in oxide film is partially reduced into Sn 2+ , whereas implanted 57 Fe 2+ is oxidized into Fe 3+ .With the increase of annealing temperatures, Sn 2+ ions are perfectly oxidized into Sn 4+ to form SnO2 rutile film.
57 Fe Ion Implantation of SnO2 Film at Substrate Temperature of 500 °C [24]   SnO2 film implanted with 5 × 10 16 Fe ions / cm 2 at 500 °C shows Kerr effect as shown in Figure 11.It is transparent Fe doped SnO2 film with high electric resistance.Two magnetic sextets with broad peaks observed in Figure 12 (left side) are due to fine Fe3O4.The implanted ions are segregated into a cluster at the high temperature.CEM spectra of Figure 12, (a), (b) and (c) are obtained by discriminating the energy of inner conversion electrons emitted after Mössbauer effect.The low energy electrons detected reflect the deep layer because the energy of the inner conversion electrons is lost by the upper layers, whereas the high energy electrons without the energy loss reflect the top surface layer.The two doublets of Fe 3+ and Fe 2+ are observed in CEM spectra.It is found from their relative intensity that the Fe 2+ species is located in deeper layer than in top surface layers, and that magnetite is more produced in the surface layers.Even if the sample was further heated at 400 °C, the ferromagnetic behavior did not disappear.The CEM spectra of the annealed sample showed one broad sextet in addition to two doublets of Fe 2+ and Fe 3+ .This broad sextet is due to fine maghemite (γ-Fe2O3).Peak intensity of paramagnetic Fe 2+ in deep layers is not so affected by annealing in air although the peak intensity of paramagnetic Fe 2+ decreases and the intensity of paramagnetic Fe 3+ increases in top surface layers.The fine magnetite in surface layers is oxidized directly into a maghemite by annealing.
CEM spectra of 3 % Sb doped SnO2 film implanted with 57 Fe are the same as the CEM spectra of 1 % Sb doped SnO2 film implanted with 57 Fe although each intensity is different.It was found that 3 % Sb doped SnO2 film is oxidized harder than 1 % Sb doped SnO2 film because the relative intensity of magnetite in the former is smaller than that of the latter.The detail analysis of 3 % Sb doped SnO2 film implanted with 57 Fe and further annealed at the high temperatures is referred. [25]uper Dilute 57 Mn Ion Implanted SnO2 Films [26] 57 Fe emission Mössbauer spectra of radioactive 57 Mn ions implanted SnO2 film are obtained on extremely dilute concentrations of < 2 × 10 -12 57 Mn / cm 2 , or < 10 -3 at % 57 Mn as shown in Figure 13.In the β-decay of 57 Mn (T½ = 1.5 min), the daughter 57 Fe is obtained by average recoil energy of ER = 40 eV, leading to the possible formation of interstitial Fe species in the case that the bond-dissociation energy is less than the recoil energy.The emission Mössbauer spectra obtained are composed of three components: (1) a doublet marked Fe(II) with a Gaussian distribution of quadrupole splitting (QS), assigned to high-spin Fe 2+ , (2) magnetic hyperfine field distribution marked Fe(III), assigned to highspin Fe 3+ showing slow paramagnetic relaxations, 3) a doublet component Fex, assigned to interstitial Fe 3+ , not metallic Fe.From the recoil imparted on the Fe atom in the β-decay of 57 Mn, it was tempting to assign Fex to interstitial Fe. [25] However, the sharp lined doublet (Fex) is interpreted due to recoil produced interstitial Fe 3+ from the isomer shift values.From the temperature dependence (143 K to 711 K) as shown in Figure 14, the activation energy for dissociation of Mn-VO pairs is estimated to be 0.9(1) eV.The is so small that the oxygen vacancy produced easily interacts Figure 11.Magneto-optical measurement of SnO2 films (a) as implanted; (b) after annealing at 400 °C. [24]gure 12.Depth CEM spectra of SnO2 films implanted with 5 × 10 16 Fe ions / cm 2 at substrate temperature of Ts = 500 °C. [24]a) as implanted; (b)  with 57 Fe.The transformation process of implanted Fe species can be suggested from the peak intensity ratios of the decomposed spectral components.
The paramagnetic Fe 2+ species, which are located in amorphous phases produced locally by 40 keV ion implantation, are oxidized into Fe 3+ at the temperatures higher than 330 K.The oxidized Fe 3+ species, which may be located in the crystalline phase at the higher temperatures, contribute to the paramagnetic relaxation peaks in the emission Mössbauer spectra.A part of the oxidized Fe 3+ species, which are recoiled and located at the interstitial sites, contribute to the sharp doublet of Fe 3+ (Fex in Figures 13 and 14).The another possible explanation is that Fe 3+ atoms that are relocated from a substitutional site due to the recoil in the β−decay in an environment characterized by a high concentration of vacancy defects can more easily be incorporated into substitutional sites.Consequently, as the defects density reduces at elevated temperatures, the probability for observing interstitial Fe 3+ increases. [26]GNETIC MOMENTS AND OXYGEN VACANCIES OF Fe DOPED SnO2 BY AB INITIO CALCULATION [27] The experimental Mössbauer parameters of Fe doped SnO2 were summarized into four groups: Fe 3+ (I1), Fe 3+ (I2), Fe 3+ (I3) and Fe 2+ (I4) (Figure 15).Groups I1 and I2 are often observed in Mössbauer spectra measured.Groups I3 and I4 are in Mössbauer spectra obtained by ion implantation and ball milling.Two main interactions (I1 and I2) observed in Mössbauer spectra can be associated to Fe-ions substituted at the Sn sites with oxygen coordination number smaller than six.That is, Fe 3+ doping into SnO2 induces oxygen vacancy.The parameters are confirmed by ab initio calculations for configurations of substituted Fe and oxygen vacancy (VO) as shown in Figures 16 and 17.The third interaction (I3) is characterized by a low IS (in the order of Figure 13. 57Fe emission Mössbauer spectra of dilute (ca. 5 × 10 -4 %) 57 Mn ion implanted SnO2 film in ISOLDE. [26]gure 14.Temperature dependence of area fraction of components: Fex: interstitial Fe 3+ , Fe(II): Fe 2+ , and Fe(III) : paramagnetic relaxation Fe 3+ . [26].20 mm s -1 (0.10 mm s -1 at RT). Fe atoms replacing Sn with oxygen vacancy are far away from the first shell of oxygen neighbours.It is not often observed in experimental data.
In the case of one Fe substituted at Sn site in SnO2 lattice and one oxygen vacancy, average Fe-ONN bondlength is in good agreement with the distances obtained from the EXAFS analysis (0.198 nm).It suggests that oxygen vacancies near the doped Fe are more stable than those near Sn in the lattice.Doping Fe ions lowers the formation energy of oxygen vacancies.The presence of an oxygen vacancy close to the Fe ions increases the split between iron 3d levels resulting in a higher magnetic moment of the Fe atoms. [27]e cases of two irons sharing oxygen vacancies are shown to search the preferential magnetic alignment as shown in Figure 17. [27]The lowest energy state for all configurations is the ferromagnetic one and in this case Fermi level falls onto minority 3d level.The doping with transition iron atoms reduces the formation energy of oxygen vacancy.Fe doped SnO2 systems will have more vacancies than the undoped ones.Oxygen vacancies enhance the magnetic moment of doped Fe impurities in supercell as listed in Table 1.
Oxygen vacancies prefer to be in the Fe-O-Fe path favoring the ferromagnetic coupling between Fe dopants.Small quantities of oxygen vacancies are fundamental for stabilizing local ferromagnetism in the form of bound magnetic polarons (BMPs).Two Fe ions sharing an oxygen vacancy are coupled ferromagnetically, forming a bound magnetic polaron (BMP), and that two neighbor BMPs are aligned antiparallel to each other although the formation energy is so very small as shown Figure 18. [27]gure 15.Isomer shift () and quadrupole splitting (Q) of experimental data and ab initio calculation: configurations of occupied Fe ions and oxygen vacancy (VO).The calculated values at RT shifted by ca.-0.1 mm s -1 due to secondary Doppler shifts (depending on the temperature) from as calculated ones are added in the original figure. [27]gure 16.Configuration of one substituted Fe at Sn site and one oxygen vacancy (VO) (distance between Fe and VO: Fe-VO1 < Fe-VO2< Fe-VO3) O1 and O2 correspond to oxygen atoms in the first shell of oxygen neighbors of Fe, and O3 is an oxygen in the second shell of Fe-oxygen neighbors. [27] [27]n the case of 57 Mn implanted SnO2 films, the Mössbauer spectra present two doublets, one with IS = 0.48 mm s -1 and ΔQ = 0.91 mm s -1 and the other with IS = 0.89 mm s -1 and ΔQ = 2.20 mm s -1 .Comparing with calculated values for one interstitial Fe atom, there is poor agreement between experimental and calculated results, but there is good agreement with the situation where the interstitial Fe has a substitutional iron near neighbor (configuration b with one oxygen vacancy in Table 1).

Long Range Magnetic Ordering
From the calculation of the configurations as shown Figure 18, it is found that the configuration with smaller energy is the antiferromagnetic one.Then, ferromagnetic interaction is only in short range while long range interaction is antiferromagnetic.The energy difference between both alignments is E = -0.05eV; that is, the antiferromagnetic alignment is a little favored.Thus, although an increase in iron concentration would favor a neighboring situation with the increase in the number of BMP, the antiferromagnetic BMP alignment would reduce the magnetization, which is in very good agreement with the experimental results.It is to note in experimental results that the Sb 5+ ions codoping of SnO2 (Fe 3+ ) increases the saturation magnetization.The electron doping was simulated in two different ways: adding one electron to the 108-atom supercell (SC) or replacing Table 1.Calculated hyperfine parameters δ and |ΔQ|; magnetic moment in the super cell (μ SC ) for the different vacancy positions studied.S: Substitutional and I: Interstitial. [27]NV, 1VO, and 2VO indicate the cases without oxygen vacancies or one or two oxygen vacancies in the super cell (SC).In the case of Configuration b with one oxygen vacancy, the results for the δ, the |ΔQ|, and μ imp refers to each inequivalent Fe site of the structure.ferromagnetic alignment among BMPs.Open circles indicates the position of the oxygen vacancies. [27]ne indigenous Sn atom by a donor impurity such as Sb 5+ .Both approaches suggest that the ferromagnetic coupling between BMP is the most stable configuration with E = Eanti -Eferro on the order of +0.3 eV.This result shows that electron doping plays a fundamental role in mediating the nonlocal magnetic coupling between two BMP.From the experimental results it was considered that the overall magnetic properties of TM-doped SnO2 are a statistical average of different defect configurations corresponding to a real disordered system. [27]

SUMMARY
The intrinsic DMS and extrinsic DMS have been experimentally obtained for dilute iron doped SnO2.Concerning intrinsic DMS, oxygen vacancies are fundamental for the ferromagnetic response of Fe-doped SnO2.The ab initio calculations show the possibility that two Fe ions sharing an oxygen vacancy are coupled ferromagnetically, forming a bound magnetic polaron (BMP), and that two neighbor BMPs are aligned antiparallel to each other.However, the formation energy for the antiferromagnetic alignment is so small that electron doping by Sb 5+ can play a fundamental role of mediating the magnetic coupling between the BMP inducing ferromagnetic alignment between the BMPs. [27] codoping two transition metals in SnO2 also enhances the dilute ferromagnetism together with inducing the oxygen vacancies, and the ab initio calculation for these configurations would be studied in near future.
As the new composite material, the nano magnetic material precipitated in semiconductors, such as SnO2 film obtained by Fe ion implantation, would be useful from the view point of practical application.
Acknowledgment.This paper presents a review article based on the author talk about oxygen defects and diluted magnetism of SnO2 doped with Fe which was presented at the Mediterranean Conference on the Applications of Mössbauer Effect, MECAME 2015, Zadar, Croatia.MECAME 2015 was organized in honour of Dr. Svetozar Musić on the occasion of his 70 th birthday and to celebrate his life-long scientific contribution, particularly for his introduction of Mössbauer spectroscopy as a research technique in Croatia.Dr. Svetozar Musić has worked in the field of metal oxides chemistry for more than four decades and especially in the iron oxide chemistry.Author of this article had worked with him on the Mössbauer analysis of iron oxide nano-powders.As the result of this collaboration the common papers were published and are listed in the references. 28These nanoscale oxide materials are expected to be used for producing new spintronic materials by embedding them into semiconductors.Author would like to express many thanks to Dr. S. Music for giving him a chance for this research field.
Prof. Cesar Barrero from the Universidad de

Figure 1 .
Figure 1.(a) Magnetic hysteresis of 10 at % Fe doped SnO2 annealed at various temperatures for 2 hours; (b) Mössbauer spectra of the sample annealed at 500 °C, (c) the sample annealed at 600 °C; and (d) the sample annealed at 650 °C.[13]

Figure 17 .
Figure 17.Configurations of Sn, Fe, O and Oxygen vacancy (VO) in rutile structure of SnO2 doped with Fe.Part of the 2 × 2 × 2 super cell (SC) showing the different distribution of the Fe atoms (black balls) substituted at Sn sites.Configuration a: Fe-2VO-Fe; configuration b: Fe-VO-Fe; and configuration c: Fe-2VO-Fe.[27]

Figure 18 .
Figure 18.Part of the 3 × 2 × 3 SC showing the bound magnetic polaron model for (a) antiferromagnetic alignment and (b) ferromagnetic alignment among BMPs.Open circles indicates the position of the oxygen vacancies.[27]