Exchange Interactions in Bcc Co: Implications for Temperature Dependence of TMR

Yuasa recently constructed Co/MgO/Co magnetic tunneling junctions (MTJs) with bcc Co(100) electrodes. These MTJs exhibited a magnetoresistance ratio of 410% at room temperature, and 507% at 20 K. The weak temperature dependence in comparison to Fe based electrodes led them to speculate that the weak temperature dependence may be due to exceptionally strong exchange interactions in bcc Co. Here we report on a theoretical investigation of the nearest neighbour exchange interactions in bcc Co