*3.4.1 RTFM in Zn0.94Cr0.06O nanorods*

The Zn0.94Cr0.06O nanorods were synthesized by a radio frequency magnetron sputtering deposition technique at different substrate temperatures [46]. The Cr K-edge X-ray absorption near-edge structure and X-ray photoelectron spectroscopy (XPS) results revealed that the Cr3+ ions are located at the substitutional Zn sites. The magnetization versus the magnetic field (M-H) loops of Zn0.94Cr0.06O nanorods measured at room temperature is shown in **Figure 6a**. The moment per Cr atom increases with the increasing substrate temperature. The sample prepared at room temperature has a net moment of 0.76 μB/Cr. With increasing substrate temperature to 650°C, the value of magnetic moment shows a remarkable increase to 1.16 μB/Cr. The coercive field, Hc, of Zn0.94Cr0.06O nanorod grown at room temperatures, 300, 500, and 650°C, are around 104, 42, 53, and 82 Oe, respectively.

#### **Figure 6.**

*(a) M-H hysteresis of Zn0.94Cr0.06O nanorods. SQUID measurements: Magnetic moment (b) with temperature (c) with applied field, for ZnO/Mn nanowires. (d) M-H plots for ZnO/(Mn, Dy) nanoparticles (adapted from [24, 44, 46]).*

*Diluted Magnetic Semiconductor ZnO: Magnetic Ordering with Transition Metal… DOI: http://dx.doi.org/10.5772/intechopen.90369*

#### *3.4.2 Temperature-dependent magnetization in Mn(1 atom%)/ZnO nanowires*

The Mn(1 atom%)-doped ZnO nanowires were synthesized by a gas phase surface diffusion process using MBE system [44]. **Figure 6c** shows the M-H hysteresis loops measured at T = 10, 100, 200, 300, and 350 K for an assembly of Mndoped ZnO nanowires. The extracted Ms is 2.2 μB/Mn ion at 10 K and reduces to 1.4 μB/Mn ion at 300 K. Both values are smaller than the theoretical value of 5 μB/Mn ion of Mn2+ state [1]. The temperature-dependent magnetization (**Figure 6b**) via ZFC and FC at H = 100 Oe shows a typical FM behavior while no intersection is observed in the temperature region of 10–400 K, which reaffirms that Tc is higher than 400 K. However, these FC/ZFC curves show the blocking temperature at Tb = 90 K. The existence of the blocking temperature may result from intrinsic defects, such as oxygen vacancies [47], which contribute weak intrinsic ferromagnetism. The bifurcation begins to increase as the temperature goes below 100 K, and the effect of the external magnetic field starts to overcome the thermal fluctuation and dominate the overall magnetization when the temperature is lower than 100 K.

#### *3.4.3 Magnetism with simultaneous doping from Mn and Dy in DMS ZnO*

**Figure 6d** shows the magnetic results at room temperature with simultaneous doping of Mn and Dy in ZnO nanoparticles prepared by sol–gel process (Mn = 0 and 2% and Dy = 0, 2, 4, and 6%) [24]. The M-H results show that as doping concentration of Dy is increased, magnetic behavior changes from weak ferromagnetic/ superparamagnetic to ferromagnetic states. The observed magnetic behavior is linked with oxygen vacancies as determined with EXAFS and PL measurements. The oxygen vacancy-mediated exchange interaction between the Dy3+ ions is due to the formation of BMPs.

**Figure 7.** *(a) M-H hysteresis for ZnO/Sm nanoparticles. (b) M-H hysteresis for ZnO/Nd. (c) SQUID M(T) behavior for ZnO/Gd (adopted from [29, 42, 43]).*

supercell and 3 μ<sup>B</sup> per unit cell, and the two Nd atoms are ferromagnetically coupled. It is found that the magnetism mainly comes from the 4f electrons of Nd ions with the local spin moment of 3 μB, and both Zn and O atoms have nearly zero spin contribution. Moreover, significant hybridization is observed between Nd 4f and O 2p orbitals, which leads to the superexchange interaction between two magnetic Nd ions mediated by the nonmagnetic O ions. Both O and Zn vacancies are considered, and it is found that VZn can enhance the magnetism of about 1 μ<sup>B</sup> as compared with defect-free system. This enhanced magnetism mainly comes from

The Zn0.94Cr0.06O nanorods were synthesized by a radio frequency magnetron sputtering deposition technique at different substrate temperatures [46]. The Cr K-edge X-ray absorption near-edge structure and X-ray photoelectron spectroscopy (XPS) results revealed that the Cr3+ ions are located at the substitutional Zn sites. The magnetization versus the magnetic field (M-H) loops of Zn0.94Cr0.06O nanorods measured at room temperature is shown in **Figure 6a**. The moment per Cr atom increases with the increasing substrate temperature. The sample prepared at room temperature has a net moment of 0.76 μB/Cr. With increasing substrate temperature to 650°C, the value of magnetic moment shows a remarkable increase to 1.16 μB/Cr. The coercive field, Hc, of Zn0.94Cr0.06O nanorod grown at room temperatures, 300, 500, and 650°C, are around 104, 42, 53, and 82 Oe,

*(a) M-H hysteresis of Zn0.94Cr0.06O nanorods. SQUID measurements: Magnetic moment (b) with temperature (c) with applied field, for ZnO/Mn nanowires. (d) M-H plots for ZnO/(Mn, Dy) nanoparticles (adapted from*

the unsaturated 2p orbitals of the surrounding O atoms.

**3.4 DMS ZnO with TM = Cr and Mn ions**

*3.4.1 RTFM in Zn0.94Cr0.06O nanorods*

*Magnetic Materials and Magnetic Levitation*

respectively.

**Figure 6.**

**120**

*[24, 44, 46]).*

### **3.5 DMS ZnO with RE ions**

### *3.5.1 RTFM in Sm/ZnO*

The RTFM is enhanced with Sm doping into ZnO is given by M-H hysteresis at room temperature (**Figure 7a**) [29]. It infers that ferromagnetism is intrinsic and formed due to the percolation of BMPs. These BMPs are made up with magnetic cations and defect carrier. A very weak ferromagnetism is observed in pristine ZnO, which is the effect of Zni and/or oxygen vacancy defects rather Zn vacancies (VZn). Because the formation energy of VZn is too high, it is not preferably formed in ZnO [48].

#### *3.5.2 RTFM in Nd/ZnO*

The pure and Nd-doped ZnO nanoparticles were synthesized by the coprecipitation method, and the magnetic results are shown by M-H hysteresis (**Figure 7b**) [42]. All the M-H hysteresis exhibited weak ferromagnetism at room temperature. However, the magnetization increases with increasing Nd3+ concentration. The value of saturation magnetization, MS, is (emu g<sup>1</sup> ) = 0.041, 0.051, and 0.069, respectively, for Zn0.97Nd0.03O, Zn0.94Nd0.06O, and Zn0.91Nd0.09O. The concentration of oxygen vacancies has a major role in mediating FM exchange interaction among Nd3+ ions. It is revealed that O vacancies and Zn interstitials are generated with an increase in Nd3+ doping to induce long-range ferromagnetism consistent with the BMP model. Moreover, the s-f coupling between the RE ions (f) and the ZnO host(s) states contributed ferromagnetism of DMSs [14]. The coercivity is also increased with Nd3+ concentration.

like shape and size of nanostructures, concentration of dopants, and lattice defects. Furthermore, an F-center exchange (FCE) mechanism has been employed to illustrate the ferromagnetism of Fe-doped ZnO nanorods [51]. In this mechanism, the

*(a) M-H hysteresis at room temperature for Zn1-*x*Fe*x*O nanorods. (b) XPS spectrum of Zn0.94Fe0.03Ce0.03O*

*Diluted Magnetic Semiconductor ZnO: Magnetic Ordering with Transition Metal…*

*DOI: http://dx.doi.org/10.5772/intechopen.90369*

vacancy to make an F-center, where the electron occupies an orbital (pz), which

between the ferromagnetic and paramagnetic or antiferromagnetic components lead to variations in saturation magnetization. Another mechanism is related with

**Figure 8b** shows Fe 2p XPS spectra in a binding energy 707–728 eV of Zn0.94Fe0.03Ce0.03O (ZFCeO) nanoparticles to find their contribution into ferromagnetism [40]. The Fe2+ and Fe3+ 2p3/2 peaks always show satellite peaks at 6 and 8 eV above the principal peaks at 709.5 and 711.2 eV, respectively. The satellite peak is found in energy region of 6–8 eV above 2p3/2 principal peak, which indicates that ZFCeO DMS has Fe coexisting in both Fe2+ and Fe3+ states. For this, a multiple fitting of Fe 2p peaks with satellites show peaks corresponding to Fe2+ (709.60 and 722.51 eV) and Fe3+ (710.82 and 723.97 eV). It indicates that the Fe ions have mixed valences of +2 and + 3. The peaks related with 2p3/2 709.89 eV and 2p1/2 723.35 eV are also observed. Therefore, it is found that the Fe exists in mixed Fe2+ and Fe3+ oxidation states to give RTFM due to Fe2+-Fe3+ transitions via oxygen vacancies.

The magnetic results for Zn0.95Fe0.05O (ZFO5) and Zn0.92Fe0.05La0.03O

0.0064 with Hc(Oe) = 12 and 144, respectively, are reported. The origin of observed magnetism at room temperature for La-doped ZFO5 is described via ZFC and FC magnetization SQUID measurement. **Figure 8c** shows temperature-dependent ZFC

) = 0.328 and 0.044 and Mr(emu g�<sup>1</sup>

) = 0.0083 and

BMP formation by the alignment of the spins in TM ions [14].

*3.6.2 Valence states of Fe in DMS ZnO influenced magnetic ordering*

*3.6.3 Magnetic ordering with La ions in Fe/ZnO nanoparticles*

(ZFLaO53) with Ms(emu g�<sup>1</sup>

**123**

*<sup>O</sup>* � *Fe*<sup>3</sup><sup>þ</sup> group is common for which an electron is trapped in the oxygen

*) M(H) for Zn0.92Fe0.05La0.03O nanoparticles (adapted from [21, 40, 50]).*

*<sup>z</sup>* orbital of the *d* shells of both iron neighbors. The interactions

*Fe*<sup>3</sup><sup>þ</sup> � *<sup>V</sup>*<sup>2</sup>�

**Figure 8.**

overlaps the *d*<sup>2</sup>

*nanostructures. (c) M(T) and (c*<sup>0</sup>

#### *3.5.3 Temperature-dependent magnetization in Gd/ZnO*

Ney et al. [43] reported that for small doping concentrations (1.3% Gd), a large fraction of the Gd atoms is substitutional on Zn lattice sites within wurtzite structure. The magnetic behavior is purely paramagnetic with magnetic moment 7 μB*/*Gd. **Figure 7c** shows the temperature-dependent magnetization from SQUID measurement for Gd-doped ZnO with different Gd concentrations using FC and ZFC conditions [43]. No separation between FC and ZFC magnetization occurs at any temperature, which provides no evidence for ferromagnetic-like behavior. Therefore, all samples have to be considered as paramagnetic. This is in contrast to previous work, where signs of ferromagnetic-like behavior are found for Gd-doped ZnO [49].

#### **3.6 DMS ZnO with Fe and La ions**

#### *3.6.1 RTFM in Fe/ZnO nanorods*

The Zn1-*x*Fe*x*O (ZFO) [*x* = 0.01 (ZFO1), 0.03 (ZFO3), and 0.05 (ZFO5)] nanorods were synthesized by a sol-gel process [50]. The XRD pattern revealed the hexagonal wurtzite structure with Fe doping. TEM images show nanorod formation with an average diameter, D(nm) = 10, 48, 14, and 12, and length, L(nm) = 23, 113, 50, and 30, respectively, for ZnO, ZFO1, ZFO3, and ZFO5. **Figure 8a** shows M-H hysteresis for pure and Fe-doped ZnO at room temperature. Pure ZnO exhibits diamagnetic behavior, whereas ZFO samples display superferromagnetic behavior. The values of are Ms(emu g<sup>1</sup> ) = 0.233, 0.459, and 0.328, respectively, measured for ZFO1, ZFO3, and ZFO5 nanorods. The variations in MS values depend on factors

*Diluted Magnetic Semiconductor ZnO: Magnetic Ordering with Transition Metal… DOI: http://dx.doi.org/10.5772/intechopen.90369*

#### **Figure 8.**

**3.5 DMS ZnO with RE ions**

*Magnetic Materials and Magnetic Levitation*

The RTFM is enhanced with Sm doping into ZnO is given by M-H hysteresis at room temperature (**Figure 7a**) [29]. It infers that ferromagnetism is intrinsic and formed due to the percolation of BMPs. These BMPs are made up with magnetic cations and defect carrier. A very weak ferromagnetism is observed in pristine ZnO, which is the effect of Zni and/or oxygen vacancy defects rather Zn vacancies

(VZn). Because the formation energy of VZn is too high, it is not preferably

The pure and Nd-doped ZnO nanoparticles were synthesized by the coprecipitation method, and the magnetic results are shown by M-H hysteresis (**Figure 7b**) [42]. All the M-H hysteresis exhibited weak ferromagnetism at room temperature. However, the magnetization increases with increasing Nd3+ concen-

0.069, respectively, for Zn0.97Nd0.03O, Zn0.94Nd0.06O, and Zn0.91Nd0.09O. The concentration of oxygen vacancies has a major role in mediating FM exchange interaction among Nd3+ ions. It is revealed that O vacancies and Zn interstitials are generated with an increase in Nd3+ doping to induce long-range ferromagnetism consistent with the BMP model. Moreover, the s-f coupling between the RE ions (f)

and the ZnO host(s) states contributed ferromagnetism of DMSs [14]. The

Ney et al. [43] reported that for small doping concentrations (1.3% Gd), a large fraction of the Gd atoms is substitutional on Zn lattice sites within wurtzite structure. The magnetic behavior is purely paramagnetic with magnetic moment 7 μB*/*Gd. **Figure 7c** shows the temperature-dependent magnetization from SQUID measurement for Gd-doped ZnO with different Gd concentrations using FC and ZFC conditions [43]. No separation between FC and ZFC magnetization occurs at any temperature, which provides no evidence for ferromagnetic-like behavior. Therefore, all samples have to be considered as paramagnetic. This is in contrast to previous work, where signs of ferromagnetic-like behavior are found for Gd-doped

The Zn1-*x*Fe*x*O (ZFO) [*x* = 0.01 (ZFO1), 0.03 (ZFO3), and 0.05 (ZFO5)] nanorods were synthesized by a sol-gel process [50]. The XRD pattern revealed the hexagonal wurtzite structure with Fe doping. TEM images show nanorod formation with an average diameter, D(nm) = 10, 48, 14, and 12, and length, L(nm) = 23, 113, 50, and 30, respectively, for ZnO, ZFO1, ZFO3, and ZFO5. **Figure 8a** shows M-H hysteresis for pure and Fe-doped ZnO at room temperature. Pure ZnO exhibits diamagnetic behavior, whereas ZFO samples display superferromagnetic behavior.

ZFO1, ZFO3, and ZFO5 nanorods. The variations in MS values depend on factors

) = 0.233, 0.459, and 0.328, respectively, measured for

) = 0.041, 0.051, and

tration. The value of saturation magnetization, MS, is (emu g<sup>1</sup>

coercivity is also increased with Nd3+ concentration.

*3.5.3 Temperature-dependent magnetization in Gd/ZnO*

*3.5.1 RTFM in Sm/ZnO*

formed in ZnO [48].

ZnO [49].

**122**

**3.6 DMS ZnO with Fe and La ions**

*3.6.1 RTFM in Fe/ZnO nanorods*

The values of are Ms(emu g<sup>1</sup>

*3.5.2 RTFM in Nd/ZnO*

*(a) M-H hysteresis at room temperature for Zn1-*x*Fe*x*O nanorods. (b) XPS spectrum of Zn0.94Fe0.03Ce0.03O nanostructures. (c) M(T) and (c*<sup>0</sup> *) M(H) for Zn0.92Fe0.05La0.03O nanoparticles (adapted from [21, 40, 50]).*

like shape and size of nanostructures, concentration of dopants, and lattice defects. Furthermore, an F-center exchange (FCE) mechanism has been employed to illustrate the ferromagnetism of Fe-doped ZnO nanorods [51]. In this mechanism, the *Fe*<sup>3</sup><sup>þ</sup> � *<sup>V</sup>*<sup>2</sup>� *<sup>O</sup>* � *Fe*<sup>3</sup><sup>þ</sup> group is common for which an electron is trapped in the oxygen vacancy to make an F-center, where the electron occupies an orbital (pz), which overlaps the *d*<sup>2</sup> *<sup>z</sup>* orbital of the *d* shells of both iron neighbors. The interactions between the ferromagnetic and paramagnetic or antiferromagnetic components lead to variations in saturation magnetization. Another mechanism is related with BMP formation by the alignment of the spins in TM ions [14].

### *3.6.2 Valence states of Fe in DMS ZnO influenced magnetic ordering*

**Figure 8b** shows Fe 2p XPS spectra in a binding energy 707–728 eV of Zn0.94Fe0.03Ce0.03O (ZFCeO) nanoparticles to find their contribution into ferromagnetism [40]. The Fe2+ and Fe3+ 2p3/2 peaks always show satellite peaks at 6 and 8 eV above the principal peaks at 709.5 and 711.2 eV, respectively. The satellite peak is found in energy region of 6–8 eV above 2p3/2 principal peak, which indicates that ZFCeO DMS has Fe coexisting in both Fe2+ and Fe3+ states. For this, a multiple fitting of Fe 2p peaks with satellites show peaks corresponding to Fe2+ (709.60 and 722.51 eV) and Fe3+ (710.82 and 723.97 eV). It indicates that the Fe ions have mixed valences of +2 and + 3. The peaks related with 2p3/2 709.89 eV and 2p1/2 723.35 eV are also observed. Therefore, it is found that the Fe exists in mixed Fe2+ and Fe3+ oxidation states to give RTFM due to Fe2+-Fe3+ transitions via oxygen vacancies.

#### *3.6.3 Magnetic ordering with La ions in Fe/ZnO nanoparticles*

The magnetic results for Zn0.95Fe0.05O (ZFO5) and Zn0.92Fe0.05La0.03O (ZFLaO53) with Ms(emu g�<sup>1</sup> ) = 0.328 and 0.044 and Mr(emu g�<sup>1</sup> ) = 0.0083 and 0.0064 with Hc(Oe) = 12 and 144, respectively, are reported. The origin of observed magnetism at room temperature for La-doped ZFO5 is described via ZFC and FC magnetization SQUID measurement. **Figure 8c** shows temperature-dependent ZFC and FC measurement with H = 500 Oe. The superimposition of ZFC/FC plots between 150 and 300 K, as well as their clear separation at low temperature with blocking temperature, TB is observed. The observed TB might correspond with Néel temperature, TN (�42 K) of AF [52]. For more detail, M-H hysteresis is also measured at 200, 100, 50, and 10 K (**Figure 8c**<sup>0</sup> ). The values Ms and Mr are enhanced with temperature when going from 300 to 10 K. This is due to the exchange interaction from AF to FM states. It is also shown that for 200–50 K, Hc varies so slowly, but at 10 K, it abruptly increased to 117 Oe, which is smaller than 144 Oe that is observed at room temperature. It means after AF transition, there is some possibility of FM clustered growth in ZFLaO sample [53]. The localization of electrons in magnetic clusters leads to develop high-spin and low-spin intersite electronic transitions. These magnetic clusters may also result from magnetic polarons [54].

AF interaction establishment following 4f-5d-3d transition in Co and RE ions,

*Diluted Magnetic Semiconductor ZnO: Magnetic Ordering with Transition Metal…*

and L(nm) = 57 � 5. **Figure 9b** (inset) showed the RTFM of Ms (emu g�<sup>1</sup>

occupying an orbital overlapping with the *d* shells of Co neighbors.

*3.7.3 Valence states of Co and O ions in Zn0.996Co0.004O nanoparticles*

the inset of **Figure 9b** with Ms(emu g�<sup>1</sup>

The Zn0.996Co0.004O (ZCO04) nanoparticles synthesized with sol–gel process for which free-charge carriers and oxygen vacancies might induce long-range ferromagnetic ordering [15]. The XRD pattern results into wurtzite structure of ZCO04. The ZCO04 crystalline product has nanorod formation with D(nm) = 23 � 3

diamagnetic [50]. Xu et al. [57] reported RTFM with higher surface-to-volume ratio of nanostructure, which contribute large amount of surface oxygen vacancies defects. It is expected that the RTFM is attributed via exchange interactions among unpaired electron spins arising from either vacancies or surface defects, which is explained on the basis of donor impurity band exchange model form BMPs [58]. It is theoretically investigated that the oxygen vacancies have remarkable change in band structure of host oxides to induce ferromagnetism [59]. For this case of BMPs, the electrons are locally trapped by oxygen vacancies, with the trapped electron

To evaluate the origin of RTFM of ZCO04 nanoparticles, the temperaturedependent magnetization is given in **Figure 9b** via ZFC and FC at H = 500 Oe. The separation between ZFC and FC starts increasing with reducing temperature from 300 to 5 K which indicates antiferromagnetic interactions converted to ferromagnetic state. The absence of blocking temperature in ZFC might indicate long-range antiferromagnetism without any cluster growth. The exchange interactions between neighboring magnetic ions mediated by an F-center form a BMP contributing long-range ferromagnetism. At 10 K, the magnetic hysteresis is also shown in

) = 0.0038 with Hc = 54 Oe. However, the pure ZnO nanorods are

) = 0.0154 and Mr(emu g�<sup>1</sup>

. The values of binding energy, Co 2p3/2 � 780.019 eV,

**, b**<sup>00</sup> shows the XPS spectra for Co 2p and O 1 s of Zn0.996Co0.004O

(ZCO04) nanoparticles. For Co 2p, the doublet is the spin-orbit coupling (2p3/2 and

2p1/2 � 795.51 eV, and ΔE � 15.51 eV, and satellite peak (S) � 785.48 eV are observed. The binding energies of Co 2p3/2 and 2p1/2 indicate that the Co ions exist either in +3 or + 2 valence states [60]. The difference ΔE of binding energy among Co 2p3/2 and 2p1/2 levels corresponds well with Co2+ that is homogeneously surrounded by oxygen in tetrahedral coordination [61]. However, the peak S is found in the energy region of 6–8 eV above the principle peak Co 2p3/2 and the value of S � 6 eV. It indicates the formation of multiple coordinations, i.e., tetrahedral or octahedral Co2+ ions. For more clarification, Co 2p peaks shown by

*<sup>o</sup>* ) and Co3+ and tetrahedral Co2+ (*Co*<sup>2</sup><sup>þ</sup>

To find defects/vacancies in ZCO04, the O 1 s spectra is shown in **Figure 9b**00, which deconvoluted into three peaks (Oa, Ob, Oc) [15]. The peak located on lowbinding energy side, Oa � 528.79 eV, is attributed with O2� ions in wurtzite structure. This Oa of O 1 s is associated with Zn-O bonds. The Ob peak at 531.19 eV is associated with O2� ions in the oxygen-deficient regions within the ZnO matrix, which indicate defect formation. The Oc peak at 532.16 eV is attributed to

) 0.0062

) = 0.002 with

*<sup>t</sup>* ) are clearly marked.

suggested by Singh et al. [56].

*DOI: http://dx.doi.org/10.5772/intechopen.90369*

and Mr (emu g�<sup>1</sup>

Hc(Oe) = 93.

**Figures 9b**0

2p1/2) given in **Figure 9b**<sup>0</sup>

octahedral Co2+ (*Co*<sup>2</sup><sup>þ</sup>

**125**

chemisorbed oxygen on the surface of the ZnO.

*3.7.2 Magnetic ordering in Zn0.996Co0.004O nanoparticles*

#### **3.7 DMS ZnO with Co, La, Gd, and Ce ions**

## *3.7.1 RTFM in La- and Gd-doped Zn0.95Co0.05O nanostructure*

**Figure 9a** shows the M-H hysteresis for Zn0.95Co0.05O (ZCO5), Zn0.92Co0.05La0.03O (ZCLO53), and Zn0.92Co0.05Gd0.03O (ZCGO53) nanostructure, measured at room temperature [36]. The pure ZCO5 shows weak ferromagnetism of Ms(emu g�<sup>1</sup> ) = 0.354 and Mr(emu g�<sup>1</sup> ) = 0.0276 with Hc(Oe) = 40 Oe. However, the La- and Gd-doped ZCO5 result into paramagnetic-type behavior. The weak ferromagnetism in ZCO5 exists due to antiferromagnetic, AF interactions among Co2+ ions [41, 55]. The AF coupling between Co impurities is favored when Co atoms are separated by more than a ZnO unit. While the ferromagnetic coupling is stable if AF interaction in neighboring Co–Co ions falling into contour of BMPs. However, the observed paramagnetism in La- and Gd-doped ZCO5 is related with

#### **Figure 9.**

*(a) M-H hysteresis for Co-, La-, and Gd-doped ZnO nanoparticles, measured at room temperature. (b) M(T) and M(H) (inset) for Zn0.996Co0.004O (ZCO04) nanoparticles. (b*<sup>0</sup> *and b*00*) XPS spectra for Co 2p and O 1 s. (c) Temperature-dependent* AC *magnetic susceptibility (χ) of ZFCeO nanoparticles (adopted from [15, 36, 40]).*

*Diluted Magnetic Semiconductor ZnO: Magnetic Ordering with Transition Metal… DOI: http://dx.doi.org/10.5772/intechopen.90369*

AF interaction establishment following 4f-5d-3d transition in Co and RE ions, suggested by Singh et al. [56].
