A Fe doped rutile TiO2 single crystal is grown in an O2 atmosphere by the floating zone technique. Electron spin resonance （ESR） spectra clearly demonstrate that Fe^3＋ ions are substituted for the Ti^4＋ ions in the rutile TiO2 matrix. Magnetization measurements reveal that the Fe：TiO2 crystal shows paramagnetic behaviour in a temperature range from 5 K to 350 K. The Fe^3＋ ions possess weak magnetic anisotropy with an easy axis along the c axis. The annealed Fe：TiO2 crystal shows spin-glass-like behaviours due to the aggregation of the ferromagnetic clusters.
The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L10 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe49Pt51/Fe bi-layers by their exchange coupling.
The influence of surface/interface roughness on the magnetic properties of Fe/Ni multilayers is investigated.Two methods are employed to tune the film roughness:one varies the substrate temperature,and the other pre-deposits a Ag underlayer on the MgO substrate.For films with higher roughness,a marked rise in coercivity is observed.Three factors are discussed to be mainly responsible for the coercivity rise,involving the formation of pinholes,the reduction of exchange coupling between Fe and Ni layers,and Fe-Ni alloying at interfaces.
LUO Zhi-YuanTANG JiaMA BinZHANG Zong-ZhiJIN Qing-YuanWANG Jian-Ping
A number of zinc oxide（Zn O） films are deposited on silicon substrates using the magnetron sputtering method.After undergoing thermal treatment under different conditions, those films exhibit hexagonal wurtzite structures and different photoluminescent characteristics. Besides the notable ultraviolet emission, which is related to the free exciton effect, a distinct blue fluorescence around 475 nm is found in some special samples.The blue photoluminescence emission of the Zn O film is believed to be caused by oxygen vacancies.
The effect of Fe-doping on the magnetic properties of the ABO3-type perovskite cobaltites La0.7Ba0.3CoO3（0≤ y≤0.80） is reported. With no apparent structural change in any doped sample, the Curie temperature （Tc） and the magnetization （M） are greatly suppressed for y ≤0.30 samples, while a distinct increase in Tc for the y=0.40 sample is observed. With the further increase of Fe concentration, Tc increases monotonically. Griffiths-like phases in 0.40≤y ≤0.60 samples are confirmed. The formation of the Griffiths-like phase is ascribed to B-site disordering induced isolation of ferromagnetic （FM） clusters above Tc.
The magneto-optical Kerr effect susceptometry technique is proposed to determine the uniaxial magnetic anisotropy （UMA） constant Ku. The magnetic properties of Cu/Fe/SiO2/Si grown by dc magnetron sputtering were investigated. The in-plane uniaxial magnetic anisotropy was probed by the magneto-optical Kerr effect （MOKE）. The value of UMA, Ku = 2.5 x 103 J/m3, was simulated from the field dependence of ac susceptibility along the hard axis according to the Stoner-Wohlfarth （S-W） model, which is consistent with Ku = 2.7~ 103 J/m3 calculated from the magnetic hysteresis loops. Our results show that the magneto-optical Kerr effect susceptometry can be employed to determine the magnetic anisotropy constant owing to its high sensitivity.
Thin Mn（2 nm）/Al（2 nm） bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic T-phase forms in the buffer layers at an optimum substrate temperature. As a template it induces the growth of following MnAl film. Compared with the case of film without buffer layer, the growth of nonferromagnetic phase is suppressed and the structural and magnetic properties of MnAl film are improved. Weak dipolar inter-grain coupling is revealed in the MnAl film, and the magnetic reversal process is dominated by magnetic moment rotation.
According to density functional theory （DFT） using the plane wave base and pseudo-potential, we investigate the effects of the specific location of oxygen vacancy （Vo） in a （Ti,Co）06 distorted octahedron on the spin density and magnetic properties of Co-doped rutile Ti02 dilute magnetic semiconductors. Our calculations suggest that the Vo location has a significant influence on the magnetic moment of individual Co cations. In the case where two Co atoms are separated far away from each other, when the Vo is located at the equatorial site of a Co-contained octahedron, the ground state of the two Co cations is d6（t3g↑, t23g ↓） without any magnetic moment. However, if the Vo is located at the apical site, these two Co sites have different ground states and magnetic moments. The spin densities are also observed to be modified by the exchange coupling between the Co cations and the location of Vo. Some positive spin polarization is induced around the adjacent O ions.
[Fe/Ni]N multilayered structure grows epitaxially on the single crystalline MgO substrate. Due to the different directions of magnetic easy axes of Fe and Ni and the strong strain, large anisotropy dispersion is assumed. According to the layer model, the magnetization of Fe and Ni layers cannot follow each easy axis because of exchange coupling, and then the anisotropies are averaged out. The reduction of the effective anisotropy enhances with the decrease of periodic thickness. Thus, the coercivity of [Fe/Ni]N multilayers reduces with decreasing periodic thickness.
