Crystalline-dependent magnon torques in all-sputtered Hf/Cr2O3/ferromagnet heterostructures

TL;DR

This study demonstrates that the crystalline structure of Cr2O3 in Hf/Cr2O3/ferromagnet heterostructures significantly influences magnon torques, enabling efficient magnetization switching with reduced spin angular momentum loss.

Contribution

It reveals the dependence of magnon torque strength on Cr2O3's crystalline orientation and demonstrates practical magnetization switching using magnon torques in all-sputtered heterostructures.

Findings

Magnon torques are stronger when the Neel vector aligns parallel to spin polarization.

Perpendicular magnetization switching achieved with a critical current density of 4.09 x 10^7 A/cm^2.

Cr2O3 insertion results in lower spin angular momentum loss compared to polycrystalline NiO.

Abstract

Electron motion in spin-orbit torque devices inevitably leads to the Joule heating issue. Magnon torques can potentially circumvent this issue, as it enables the transport of spin angular momentum in insulating magnetic materials. In this work, we fabricate a sandwich structure composed of Hf/antiferromagnetic Cr2O3/ferromagnet and demonstrate that the magnon torque is strongly dependent on the crystalline structure of Cr2O3. Magnon torques are stronger when the Neel vector of Cr2O3 aligns parallel to the spin polarization generated in Hf, while they are suppressed when the Neel vector is perpendicular to the spin polarization. The magnon torque efficiency is estimated to be -0.134 using in-plane second harmonic Hall measurements. Using magnon torques, we achieve perpendicular magnetization switching of CoFeB, with a critical switching current density of 4.09 x 10^7 A/cm^2. Furthermore, the spin angular momentum loss due to the insertion of Cr2O3 is found to be lower than that of polycrystalline NiO. Our work highlights the role of antiferromagnet crystalline structures in controlling magnon torques, broadening the potential applications of magnon torques.