The electrical and magnetic properties of Zn-doped Fe(3)O(4) at different doping concentrations of Zn have been investigated using a density functional method with generalized-gradient approximation corrected for on-site Coulombic interactions. The electronic structure calculation predicts that Zn(x)Fe(3-x)O(4) (0 ≤x≤ 0.875) is half-metallic with a full spin polarization. The hopping carrier concentration of Zn(x)Fe(3-x)O(4) decreases with increasing x, which indicates a distinct increase in the resistivity. The saturation magnetization of Zn(x)Fe(3-x)O(4) increases evidently with increasing x from x = 0 to x = 0.75 (i.e. from 4.0 to 8.3 μ(B)/f.u.) and then decreases rapidly to zero at x = 1. The robust half-metallicity, large tunability of electrical and magnetic properties of a Zn doped Fe(3)O(4) system make it a promising functional material for spintronic applications.
Zn x ͑ZnO͒ 1−x granular films with nominal atomic concentration of x =0ϳ 1 were prepared by magnetron cosputtering method. Ferromagnetism is observed in films with 0.04Յ x Ͻ 0.60. The room-temperature saturated magnetization increases with increasing x and reaches its maximum value of about 3.34 emu/cc at x = 0.31. The temperature-dependent magnetization curve could be fitted within the framework of Stoner model in a large temperature range from 50 to 800 K. The obtained Curie temperature is higher than 500°C. It is found that the main point defects in ZnO are Zn interstatial and oxygen vacancy. Room-temperature photoluminescence analysis and high-temperature x-ray diffraction measurement show conclusive evidence that the native point defect of Zn interstitial plays a crucial role in the observed magnetic behaviors. By implicating the shallow donor related carriers and/or extending the charge-transfer mechanism to metal/semiconductor heterostructure, the result could be qualitatively explained based on the Stoner theory of band magnetism. These findings may help to get further insight into the ferromagnetic origin in nonmagnetic ion doped ZnO systems.
Polycrystalline Cr-doped ZnO films are prepared by the co-sputtering method. Diamagnetism is observed in the conductive samples deposited in pure Ar. However, ferromagnetism is found in films with the same Cr dopant prepared under different oxygen partial pressures. The magnetization shows a strong dependence on the Cr concentration and, especially, on oxygen pressure. It is found that native point defects, which can be adjusted by the oxygen partial pressure during deposition, play a crucial role in the observed magnetic behaviors. The obtained ferromagnetism can be described by the dopant-donor/acceptor hybridization model, which associates exchange interaction with shallow-bound carriers. These results may help to understand the wide range of experimentally determined magnetic moments and its changes with different metal types and concentrations prepared by different groups and methods.
[Fe1−δ(FeO)δ]x(TiO2)1−x (0≤δ≤0.91, 0.34≤x≤0.54) granular films were fabricated by magnetron sputtering. Large coercivity (HC = 10.5 kOe) and exchange-bias-field (HE = 6.5 kOe) at 5 K were found in the film with δ=0.84 and x = 0.48. AC susceptibility measurements exhibit a frequency (f) dependent peak Tf in the in-phase susceptibility curve. The fitting of the relation of Tf vs f with both the Vogel-Fulcher law and critical slowing down theory indicate that the evident enhancement of the HC and HE can be qualitatively ascribed to the existence of cluster-spin glass state. The results may help to deeply understand the origin of exchange bias and related effects.
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