Zheng-Long Wu

Effect of interfacial structures on anomalous Hall behavior in perpendicular Co/Pt multilayers

A large enhancement of anomalous Hall resistivity was obtained in the perpendicular [Co/Pt]3 multilayers sandwiched by MgO/CoO hybrid bilayers. For example, the saturation Hall resistivity (ρxy) is greatly increased, which is 250% and 67% larger than that in pure [Co/Pt]3 multilayers and that in [Co/Pt]3 multilayers sandwiched by pure MgO layers, respectively. Meanwhile, the perpendicular magnetic anisotropy in the multilayers with MgO/CoO hybrid bilayers was enhanced. The large enhancement of ρxy originates from the modified metal/oxide interfacial structures, together with improved crystallization of core [Co/Pt]3 multilayers, due to the insertion of hybrid bilayers.

Effect of MgO/Co interface and Co/MgO interface on the spin dependent transport in perpendicular Co/Pt multilayers

Effect of the metal/oxide interface on spin-dependent transport properties in perpendicular [Co/Pt]3 multilayers was investigated. The saturation Hall resistivity (ρxy) is significantly increased by 45% with 1.4 nm thick CoO layer inserted at the top Co/MgO interface; whereas it is increased only 25% with 1 nm thick CoO layer at the bottom MgO/Co interface. The interfacial structures characterized by X-ray photoelectron spectroscopy show that the MgO/Co interface and Co/MgO interface including chemical states play a dominant role on spin-dependent transport, leading to different anomalous Hall behavior.

Chemical reaction at ferromagnet/oxide interface and its influence on anomalous Hall effect

Chemical reactions at the ferromagnet/oxide interface in [Pt/Fe]3/MgO and [Pt/Fe]3/SiO2 multilayers before and after annealing were investigated by X-ray photoelectron spectroscopy. The results show that Fe atoms at the Fe/MgO interface were completely oxidized in the as-grown state and significantly deoxidized after vacuum annealing. However, only some of the Fe atoms at the Fe/SiO2 interface were oxidized and rarely deoxidized after annealing. The anomalous Hall effect was modified by this interfacial chemical reaction. The saturation anomalous Hall resistance (Rxy) was greatly increased in the [Pt/Fe]3/MgO multilayers after annealing and was 350% higher than that in the as-deposited film, while Rxy of the [Pt/Fe]3/SiO2 multilayer only increased 10% after annealing.

Ru Catalyst-Induced Perpendicular Magnetic Anisotropy in MgO/CoFeB/Ta/MgO Multilayered Films

The high oxygen storage/release capability of the catalyst Ru is used to manipulate the interfacial electronic structure in spintronic materials to obtain perpendicular magnetic anisotropy (PMA). Insertion of an ultrathin Ru layer between the CoFeB and Ta layers in MgO/CoFeB/Ta/MgO films effectively induces PMA without annealing. Ru plays a catalytic role in Fe-O-Ta bonding and isolation at the metal-oxide interface to achieve moderate interface oxidation. In contrast, PMA cannot be obtained in the sample with a Mg insertion layer or without an insertion layer because of the lack of a catalyst. Our work would provide a new approach toward catalyst-induced PMA for future CoFeB-based spintronic device applications.