Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions

Abstract

Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg${}_3$BO${}_4$), B atoms replacing O atoms (Mg${}_4$BO${}_3$), and B atoms occupying interstitial positions (Mg${}_4$BO${}_4$) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg${}_3$BO${}_4$ and CoFe/Mg${}_4$BO${}_4$ based MTJs, whereas a nearly symmetric STT curve is observed in the junctions based on CoFe/Mg${}_4$BO${}_3$. Furthermore, the asymmetry of the angular dependence of STT can be suppressed significantly by the disorder of B distribution. Such skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the interfacial resonance states induced by the B diffusion into MgO spacer. The present investigation demonstrates the feasibility of effectively enhancing microwave output power in MgO based spin torque oscillator (STO) by doping the B atoms into MgO spacer.

arXiv comment8 pages, 8 figures

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