Strong perpendicular magnetic anisotropy energy density at Fe alloy/HfO2 interfaces

TL;DR

This study demonstrates that inserting ultrathin HfO2 layers at Fe alloy interfaces significantly enhances perpendicular magnetic anisotropy energy density in heterostructures, with potential for spintronics applications.

Contribution

It introduces a novel interface engineering method using ultrathin HfO2 layers to achieve strong PMA without post-fabrication annealing.

Findings

Achieved 1.7 erg/cm^2 PMA energy density without annealing.

HfO2 layers fully oxidized during MgO deposition.

Thermal annealing further enhances PMA.

Abstract

We report on the perpendicular magnetic anisotropy (PMA) behavior of heavy metal (HM)/ Fe alloy/MgO thin film heterostructures after an ultrathin HfO2 passivation layer is inserted between the Fe alloy and the MgO. This is accomplished by depositing one to two atomic layers of Hf onto the Fe alloy before the subsequent rf sputter deposition of the MgO layer. This Hf layer is fully oxidized during the subsequent deposition of the MgO layer, as confirmed by X-ray photoelectron spectroscopy measurements. As the result a strong interfacial perpendicular anisotropy energy density can be achieved without any post-fabrication annealing treatment, for example 1.7 erg/cm^2 for the Ta/Fe60Co20B20/HfO2/MgO heterostructure. Depending on the HM, further enhancements of the PMA can be realized by thermal annealing to at least 400C. We show that ultra-thin HfO2 layers offer a range of options for enhancing the magnetic properties of magnetic heterostructures for spintronics applications.