Al2-xFexO3의 물리적 성질, 전자 상태와 터널자기저항 계면에서의 자성 산화물 형성에 관한 연구

Abstract

Structural, magnetic, electric and magnetoelectric properties and electronic stateshave been investigated for polycrystalline Al2&#8722

xFexO3 (0.8 ● x ● 1.2) as preparedby a solid state reaction method. Orthorhombic single phase samples were obtainedwithout secondary phases. The maximum magnetization as well as the ferrimagneticphase transition temperature (TC) increases with as increase of Fe content x, whilethe coercive force with x shows no obvious trend. Except for x = 0.8, the thermalactivation energy gap is likely to decrease with the Fe content x. Electric polarizationwith magnetic fields shows a clear linear magnetoelectric effect for x = 0.8 and1.0 but somewhat different shape for x = 1.2. Soft x-ray spectroscopy results showthat the Fe ions occupy at not only Oh (Fe1, Fe2 and Al2) but also considerably TdAl site. Moreover, Magnetic moment of Fe3+ at Td Al1 site is found to contributeoppositely to the magnetization, resulting in that direction of spins at Oh Al2 andFe2 sites are antiparallel to those at Td Al1 and Oh Fe1 sites. Unexpectedly largeangular momentum was also observed for the half-filled d5 system. A simple interpretationis presented in order to understand the high magnetic anisotropy and themagnetoelectric effect.We also investigated interfacial status between ferromagnetic Co84Fe16 and insulatingbarrier Al2O3 of the Al2O3-based magnetic tunnel junction (MTJ), usingvarious x-ray scattering measurements. The results show formation of orthorhombicAlFeO3 magnetic nanoparticles at the interface, which are embedded in the Al2O3cage. Their thickness and planner size vary with the plasma oxidation time. We alsoobserved an interesting magnetic anomaly with a minimum magnetic coercivity nearthe AlFeO3 ferrimagnetic TC, which is successfully explained in terms of the AlFeO3nanoparticles and nano-scale CoFe grains with size distribution.