Co nanowires (NWs) and nanotubes (NTs) with same length and different diameter have been deposited in anodized aluminum oxide templates by electrodeposition method at the room temperature. The Co NWs show hcp structure while Co NTs show poor crystalline with no strong texture. The spontaneous magnetization of the Co NWs was found to be parallel to the nanowires, while Co NTs have a transverse spontaneous magnetization. Magnetization reversal occurs by curling mode in Co nanotubes while nucleation mode in Co nanowires. Temperature dependent magnetic properties show that the thermal energy decreases at low temperature causing an increase in coercivity and saturation magnetization. The dominance of shape anisotropy in case of Co NWs is manifested by the weak temperature dependence of the enhanced coercive field. Magnetostatic interactions and magnetocrystalline anisotropy is found dominant in case of Co NTs due to their distinct geometry.
Perpendicular magnetic tunnel junctions (pMTJs) with tunneling magnetoresistance (TMR) as high as 14.7% at room temperature were fabricated. The continuous film and pMTJs with Co/Pt multilayer magnetic electrodes and AlOx tunnel barrier were annealed at different temperatures and the effect of annealing on their properties was investigated. The hysteresis loops and X-ray reflectivity measurement show that the interdiffusion of Co and Pt atoms is slight when annealed below 523 K. However, the patterned magnetic tunnel junction gets TMR ratio from 12.3% to the maximum value of 14.7% after annealing at 483 K for 1 h.
BiFeO3/CoFe bilayers with different BiFeO3 (BFO) crystalities were fabricated by chemical solution deposition and sputtering method. Exchange bias has been successfully induced in these bilayers by post-annealing. The annealing temperature dependence of exchange bias as well as coercivity was investigated. Two kinds of annealing temperature dependence behaviors were observed. It is found that, similar to the conventional antiferromagnet/ferromagnet system, the temperature dependence of exchange bias is dominated by direct interface coupling, and the crystality of BFO has no profound effect on exchange bias.
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