Magnetic and Free-Layer Properties of MgO/(Co)FeB/MgO Structures: Dependence on CoFeB Composition

We investigate the magnetic properties of MgO/(Co
_1-x
Fe
_x
)
₇₅
B
₂₅
/MgO trilayers with Fe composition x varied from 0.5 to 1.0 and properties of magnetic tunnel junction (MTJ) with this structure as a free layer. The interfacial and bulk anisotropy energy densities increase, and the damping constant α decreases, with increasing x. For MTJs made with this structure as the free layer, the coercive field and thermal stability factor Δ both increase with increasing x. Higher switching efficiency, defined as the ratio of Δ to intrinsic critical current, is expected for devices with higher Fe composition owing to the smaller α.