arXiv subjects

Jiangchao Qian

Publications and source records attributed to Jiangchao Qian.

4 recordsLinked to original sources

arXiv2024

Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface

We investigate the structural and electronic origin of antiferromagnetic (AFM) coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in samples prepared with surface ion milling, indicative of antiferromagnetic exchange coupling at the YIG/Py interface. Using atomic resolution scanning transmission electron microscopy (STEM), we found that AFM coupling appears at the YIG/Py interface of the tetrahedral YIG surface formed with ion milling. The STEM measurements suggest that the interfacial AFM coupling is predominantly driven by an oxygen-mediated super-exchange coupling mechanism, which is confirmed by the density functional theory (DFT) calculations to be energetically favorable. Thus, the combined experimental and theoretical results reveal the critical role of interfacial atomic structure in determining the type magnetic coupling in a YIG/ferromagnet heterostructure, and prove that the interfacial structure can be experimentally tuned by surface ion-milling.

cond-mat.mtrl-sci↗

arXiv2024

Unconventional Spin-Orbit Torques from Sputtered MoTe2 Films

Materials with strong spin-orbit coupling and low crystalline symmetry are promising for generating large unconventional spin-orbit torques (SOTs), such as in-plane field-like (FL) torques and out-of-plane damping-like (DL) torques, which can effectively manipulate and deterministically switch an out-of-plane magnetization without the need for additional external in-plane magnetic fields. Here, we report SOTs generated by magnetron-sputtered 1T' MoTe2/Permalloy (Py; Ni80Fe20)/MgO heterostructures using both spin-torque ferromagnetic resonance (ST-FMR) and second harmonic Hall measurements. We observed unconventional FL and DL torques in our samples due to spins polarized normal to the interface of MoTe2 and Py layers, and studied the influence of crystallographic order and MoTe2 layer thickness on the SOTs. By comparing the Raman spectra of 1T' MoTe2 samples prepared in different ways, we found a tensile strain in sputtered MoTe2 films, which might further enhance the generation of unconventional torques by reducing the symmetry of 1T' MoTe2.

cond-mat.mtrl-sci↗

arXiv2023

Integrating Magnons for Quantum Information

Magnons, the quanta of collective spin excitations in magnetically ordered materials, have distinct properties that make them uniquely appealing for quantum information applications. They can have ultra-small wavelengths down to the nanometer scale even at microwave frequencies. They can provide coupling to a diverse set of other quantum excitations, and their inherently gyrotropic dynamics forms the basis for pronounced non-reciprocities. In this article we discuss what the current research challenges are for integrating magnetic materials into quantum information systems and provide a perspective on how to address them.

cond-mat.mtrl-sci↗

arXiv2022

Structural and Magnetic Properties of Pt/Co/Mn-Based Multilayers

Magnetic multilayers are a rich class of materials systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here we present a comprehensive experimental study of a novel system, Pt/Co/Mn, which extends the group of Pt/Co/X ($\mathrm{X}=$ metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out-of-plane to in-plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness, suggesting the existence of bubble-like domains -- potentially even magnetic skyrmions -- in the case of sufficiently thick Mn layers, which are expected to contribute to a sizeable Dzyaloshinskii-Moriya interaction in the multilayer stacks. We identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications.

cond-mat.mtrl-sci↗