We have observed room temperature ferromagnetism in Mn-doped and (Fe, Mn)-codoped ZnO thin films grown under different oxygen partial pressures by pulsed laser deposition. The X-ray diffraction and optical transmission spectra studies demonstrate the natural incorporation of Fe and Mn cations into wurtzite ZnO lattices. The effects of transition metal doping and defects on the magnetic properties was investigated. It is found that room temperature ferromagnetism is sensitive to oxygen vacancy and Zn vacancy. The absence of ferromagnetism in pure ZnO films grown under different oxygen partial pressures reveals that the transition metal ions should also play an important role in inducing the ferromagnetism.
Microstructures and magnetic properties of Ta/Pt/Co 2 FeAl（CFA）/MgO multilayers are studied to understand perpendicular magnetic anisotropy（PMA） of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization（M s） changes because of the conversions.The dependence of M s on the annealing temperature and MgO thickness is also studied.
Pure ZnO and Zn0.96Na0.04O films were grown on quartz substrates by sol-gel technology.The XRD analysis revealed that all thin films had hexagonal wurtzite structure and obvious c-axis preferred orientation.Ferromagnetism was precisely measured by an alternating gradient magnetometer (AGM).To explore the nature original ferromagnetism,the effect of annealing atmosphere on magnetic properties of the films was studied.Compared with pure ZnO,magnetic hysteresis loops showed that doping Na atoms enhanced saturation magnetism.The mag-netism of the films annealed in the air atmosphere was significantly better than that in the O2 atmosphere.The photoluminescence (PL) spec-trum analysis suggested that the ferromagnetism was due to the defects in the films.
Wu, Kai Xu, Xiaoguang Yang, Hailing Zhang, Jianli Miao, Jun Jiang, Yong
We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using firstprinciples method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) become close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.
The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl 2 O 4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5.10 eV for MgAl 2 O 4 and 4.81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point ( band), the coherent tunneling effect might be expected to appear in MgAl 2 O 4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2.9 J m 2 ) and MgAl 2 O 4 (2.27 J m 2 ) on the {100} orientation, and the smaller lattice mismatch between MgAl 2 O 4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl 2 O 4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.
The current-driven domain wall motion was investigated on permalloy nanowires with different dimensions by micromagnetic simulations.The critical current density increased with the reduction in both the width and thickness of nanowires because of the enhanced hard-axis anisotropy.At a thickness of 5 nm,the critical current density decreased with the reduction of the nanowire width because of the reduced domain wall width.
Co2FeA10.5Si0.5 （CFAS）-based multilayers sandwiched by MgO layers have been deposited and annealed at different temperatures. Perpendicular magnetic anisotropy （PMA） with the magnetic anisotropy energy density Ku ≈2.5x106 erg/cm3 （1 erg = 10-7 J） and the coercivity He = 363 Oe （10e = 79.9775 A.m-1） has been achieved in the Si/SiO2/MgO （1.5 nm）/CFAS （2.5 nm）/MgO （0.8 nm）/Pt （5 nm） film annealed at 300 ℃. The strong PMA is mainly due to the top MgO layer. The structure can be used as top magnetic electrodes in half-metallic perpendicular magnetic tunnel junctions.
First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Znl-xBxO （0 〈 x 〈 1） systems. The nearest oxygen atoms coordinated with the B Zn vacancy pair show a few hole states in the 2p orbitals and induce magnetic moments. However, the configuration of two boron atoms inducing one Zn vacancy is nonmagnetic, with a lower formation energy than that of the B-Zn vacancy pair. This explains the difference between the theoretical and experimental magnetic moments.
