*3.3.1 Magnetic behavior of Zn1-xTMxO (T = Cr, Mn, Fe, Co, and Ni)*

The magnetic properties of Zn1-*x*TM*x*O (T = Cr, Mn, Fe, Co, and Ni) thin films are investigated using first principle calculations on the basis of DFT theory within the generalized gradient approximation (GGA) [19]. Self-consistency is achieved by allowing the total energy to converge within 1 meV because of very small-energy difference expected between the FM and AF states. **Figure 5a1–a4** shows that TM 3d levels dominate the density of states (DOS) at the Fermi energy and overlap with O 2p states. This indicates that there is a strong interaction between TM and the neighboring O atoms, which results into opposite magnetic moments of O atoms. The contribution to the moment coming from TM 3d orbitals is 2.859μB, 3.930μB, 3.189μB, 2.095μB, and 1.015μ<sup>B</sup> for TM = Mn, Cr, Fe, Co, and Ni, respectively. In the ground state configuration, the AF state is found to be lower in energy by 0.094, 0.601, 0.832, 0.098, and 0.102 eV than the FM state for Zn0.929TM0.071O with TM = Cr, Mn, Fe, Co, and Ni, respectively.

the host material occurs at the Fermi level. By introducing oxygen vacancies, the Gd f state near the Fermi energy becomes partially occupied by donor electrons. Consequently, the carrier concentration around VO is increased, which mediates the interaction between the s (mostly from Zn) and f electrons. This is evident from the DOS, as the s-f coupling is more prominent than p-f and f-f couplings. For such case, the carrier involved long-range ferromagnetic order to determine the

*isosurface (green dotted), Zn(blue), O(red), and Nd(green spheres) (adapted from [19, 28, 39]).*

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

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

*(a1–a4) partial spin DOS of TM 3d and O 2p in Zn24TM4O28 supercell. (b) DOS of Zn46O48Gd2 and*

*) Total and projected DOS of Zn51VZnO54Nd2 nanowire. Fermi level spin-density*

exchange interactions in DMS ZnO. Moreover for these Gd-doped ZnO, oxygen vacancies donate two electrons to the system, mediating the

mechanisms.

**119**

**Figure 5.**

*Zn46O47Gd2 supercell. (c, c*<sup>0</sup>

*3.3.3 Giant anisotropy in Nd/ZnO nanowire*

ferromagnetic exchange, and hence, the s-f coupling is more prominent than other

In **Figure 5c**, the origin of the giant magnetic moment and anisotropy at atomic level is performed by spin-polarized DFT calculations on Zn52O54Nd2 nanowire model using spin density (Δρ = ρ↑ � ρ↓) and the projection of DOS onto the O-2p and Nd-4f orbitals [28]. The total magnetic moment is high as 6 μ<sup>B</sup> calculated from

#### *3.3.2 Densities of states of Gd ions in ZnO*

**Figure 5b** shows the first-principle calculation for Zn46O48Gd2 and Zn46O47Gd2 nanowires with and without oxygen vacancies, VO [39]. The spin-up and spin-down DOSs of doped nanowire are significantly different from that of the pristine nanowire. The majority Gd f states (spin-up) that are located well below the valence band maximum are fully occupied. However, the minority unoccupied Gd f states are localized in the vicinity of the Fermi level. The Gd d states in the conduction band overlap with the Gd f states. The hybridization of Gd f states with the states of

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

#### **Figure 5.**

from SQUID measurements. The difference of ΔMR is up to 2.5% as the gate voltage changes from 40 to +40 V at T = 1.9 K, which suggests the electric field control

DMSs Zn0.92Fe0.05La0.03O (ZFLaO53) nanoparticles were synthesized by sol-gel process [21]. The value of nanoparticles size is 99 nm. The lattice spacing is calculated from high-resolution transmission electron microscopy (HRTEM) images (**Figure 4b**), which show that the distorted lattice has an enhanced interplanar spacing *d* [(101) planes] of 0.247 nm. It is also observed from HRTEM that some fractions within the lattice fringes are formed. This may due to some ferromagnetic clustered growth by dopants in Zn2+ lattice. The high crystallinity of the particles

The Zn0.91Ni0.05Ce0.04O (ZNiO/Ce) nanoparticles were synthesized by a sol-gel

The ZnO thin film is prepared by a sol–gel MOD method [45] with the average

The magnetic properties of Zn1-*x*TM*x*O (T = Cr, Mn, Fe, Co, and Ni) thin films are investigated using first principle calculations on the basis of DFT theory within the generalized gradient approximation (GGA) [19]. Self-consistency is achieved by allowing the total energy to converge within 1 meV because of very small-energy difference expected between the FM and AF states. **Figure 5a1–a4** shows that TM 3d levels dominate the density of states (DOS) at the Fermi energy and overlap with O 2p states. This indicates that there is a strong interaction between TM and the neighboring O atoms, which results into opposite magnetic moments of O atoms. The contribution to the moment coming from TM 3d orbitals is 2.859μB, 3.930μB, 3.189μB, 2.095μB, and 1.015μ<sup>B</sup> for TM = Mn, Cr, Fe, Co, and Ni, respectively. In the ground state configuration, the AF state is found to be lower in energy by 0.094, 0.601, 0.832, 0.098, and 0.102 eV than the FM state for Zn0.929TM0.071O

**Figure 5b** shows the first-principle calculation for Zn46O48Gd2 and Zn46O47Gd2 nanowires with and without oxygen vacancies, VO [39]. The spin-up and spin-down DOSs of doped nanowire are significantly different from that of the pristine nanowire. The majority Gd f states (spin-up) that are located well below the valence band maximum are fully occupied. However, the minority unoccupied Gd f states are localized in the vicinity of the Fermi level. The Gd d states in the conduction band overlap with the Gd f states. The hybridization of Gd f states with the states of

process [27]. **Figure 4c** shows their TEM image with an average size of

**3.3 First principle calculation for DMS ZnO with TM and RE ions**

*3.3.1 Magnetic behavior of Zn1-xTMxO (T = Cr, Mn, Fe, Co, and Ni)*

of ferromagnetism for realizing spin logic devices.

*Magnetic Materials and Magnetic Levitation*

*3.2.2 HRTEM of Zn0.92Fe0.05La0.03O nanoparticles*

is evident from the selected area electron diffraction.

*3.2.3 TEM of Zn0.91Ni0.05Ce0.04O nanoparticles*

*3.2.4 Atomic force microscopy (AFM) of pure ZnO*

with TM = Cr, Mn, Fe, Co, and Ni, respectively.

*3.3.2 Densities of states of Gd ions in ZnO*

**118**

size of nanoparticles of 40 nm (**Figure 4d**).

nanoparticles of 81 nm.

*(a1–a4) partial spin DOS of TM 3d and O 2p in Zn24TM4O28 supercell. (b) DOS of Zn46O48Gd2 and Zn46O47Gd2 supercell. (c, c*<sup>0</sup> *) Total and projected DOS of Zn51VZnO54Nd2 nanowire. Fermi level spin-density isosurface (green dotted), Zn(blue), O(red), and Nd(green spheres) (adapted from [19, 28, 39]).*

the host material occurs at the Fermi level. By introducing oxygen vacancies, the Gd f state near the Fermi energy becomes partially occupied by donor electrons. Consequently, the carrier concentration around VO is increased, which mediates the interaction between the s (mostly from Zn) and f electrons. This is evident from the DOS, as the s-f coupling is more prominent than p-f and f-f couplings. For such case, the carrier involved long-range ferromagnetic order to determine the exchange interactions in DMS ZnO. Moreover for these Gd-doped ZnO, oxygen vacancies donate two electrons to the system, mediating the ferromagnetic exchange, and hence, the s-f coupling is more prominent than other mechanisms.

#### *3.3.3 Giant anisotropy in Nd/ZnO nanowire*

In **Figure 5c**, the origin of the giant magnetic moment and anisotropy at atomic level is performed by spin-polarized DFT calculations on Zn52O54Nd2 nanowire model using spin density (Δρ = ρ↑ � ρ↓) and the projection of DOS onto the O-2p and Nd-4f orbitals [28]. The total magnetic moment is high as 6 μ<sup>B</sup> calculated from

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 unsaturated 2p orbitals of the surrounding O atoms.

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

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

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

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

the formation of BMPs.

**Figure 7.**

**121**

*ZnO/Gd (adopted from [29, 42, 43]).*

**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

*(a) M-H hysteresis for ZnO/Sm nanoparticles. (b) M-H hysteresis for ZnO/Nd. (c) SQUID M(T) behavior for*

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 DMS ZnO with TM = Cr and Mn ions**
