Hybrid Memory Layer With Low Curie Temperature CoPd/Pd Multilayer for High-Density Magnetic Random-Access Memory Cells

摘要

We investigated switching behavior of the hybrid structures consisting of low Curie temperature (T_C) and high T_Clayers. The T_Cof [Co (0.3 nm)/Pd (1.2 nm)]6 and [Co54Pd46 (0.3 nm)/Pd (1.2 nm)]6 multilayers (MLs) were confirmed to have much higher than 200 °C and around 110 °C, respectively. In the bi-ML hybrid structure with Co/Pd and CoPd/Pd MLs, the two MLs are exchange-coupled at room temperature, and the CoPd/Pd ML was switched following the magnetization of the high T Co/Pd ML at high temperature (~170 °C) at which the CoPd/Pd ML becomes paramagnetic. The tri-layered hybrid structure with a stack of [Co (0.4 nm)/Pt (1.2 nm)]6/[Co48Pd52 (0.3 nm)/Pd (1.2 nm)]3/[Co (0.4 nm)/Pd (1.2 nm)]3 was also investigated. The tri-ML stack showed one-step hysteresis loop at room temperature and two-step loop at higher than 120 °C due to the loss of magnetic order of the intermediate low T_CCoPd/Pd ML. From the data of tri-ML stack, the exchange coupled and decoupled situations between Co/Pt and Co/Pd MLs were found to be realized by changing the temperature from room temperature to around 150 °C.