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

TL;DR

This study uses first-principles calculations to explore how boron doping in MgO spacers affects the angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions, revealing asymmetric behaviors and potential for enhanced spin torque oscillators.

Contribution

It demonstrates how B doping influences the asymmetry of spin-transfer torques and suggests ways to optimize MgO-based spin torque oscillators through doping and disorder control.

Findings

Asymmetric STT dependence in B-doped MgO junctions

Symmetric STT in certain B-doped configurations

B diffusion-induced interfacial resonance states influence STT behavior

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.