자기적 이중층에서 전기장을 이용한 교환 바이어스의 특성 조절

Abstract

Spintronics has received a great deal of attention owing to their potential for advanced generation of electronic devices. In particular, Exchange bias phenomena are of remarkable benefit in information technology by utilizing the exchange interaction, which is associated with the interaction at the interface between antiferromagnetic and ferromagnetic layers. Among various exchange bias system, electrically controllable exchange bias will be able to give rise extensive background on devices which can be applied to new information storage media and spintronics.Here, we showed electric-field control of exchange bias in the NiFe2O4 (NFO)/CoFe2O4 (CFO) bi-layer. The NFO and CFO layers as a fixed layer and a free layer respectively were grown on the PMN-PT (001) single-crystal substrate. The structural analysis supports that a NFO/CFO bi-layer thin film has four-fold cubicsymmetry indicating the in-plane epitaxy, which plays a crucial role especially in the exchange interaction. It has been experimentally shown that the epitaxial films exhibit typical ferromagnetic hysteresis curves. In this system, we found that the enhancement of coercive field by exchange coupling is dependent on thickness and temperature. Also, a shift of the hysteresis loop caused by exchange bias effect could be switched in the opposite direction to the direction of magnetic poling field. Furthermore, the shift became more apparent as the film thickness of the free layer (NFO) and the fixed layer (CFO)decreased. This thickness dependent exchange bias suggests that the exchange force at the interface diminishes as the layer of thin films becomes thicker. Furthermore, we showed the exchange bias could be tuned by the electricfield-induced compressive strain from the PMN-PT (001) single-crystal at room temperature. The in-plane compressive strain under the external electric-field was transferred to the top layers and influenced on the exchange bias of the CFO/NFO bi-layer thin film. When the external electric field was applied in our sample, the exchange bias field increased by 25% with an electric field of 10kv/cm. And then, it returned to the initial value in the absence of electric-field. These results may contribute to understand the physics of exchange bias and commercialization of spintronics.