In‐situ observation of structural transition, ferromagnetic order breaking and magnetocrystalline anisotropy by EMCD in MnAs/GaAs(001)

Abstract

EMCD (Energy‐Loss Magnetic Chiral Dichoism), an emerging technique based on energy‐loss spectroscopy (EELS) in a transmission electron microscopy (TEM) [1‐2], aims at measuring the element‐specific local magnetic moment of solids at a nanometer scale. The signal of interest that brings the magnetic information comes from two chiral positions in the electron diffraction pattern, as sketched in figure 1(a). In this work, EMCD is carried out to epitaxial MnAs thin films grown on a GaAs(001) substrate. As illustrated in figure 1(b‐c), a breaking of the ferromagnetic order in MnAs thin film is locally studied in‐situ, together with the associated crystallographic transition from hexagonal α‐MnAs to quasi‐hexagonal β‐MnAs, by modifying the temperature of the crystal inside the electron microscope. To achieve quantitative information, applying the sum rules [3] to the dichroic signal of magnetic anisotropic materials is accurately discussed [4]. In addition, the orbital‐to‐spin moment ratio of ‐MnAs along the easy, hard, and intermediate magnetic axes is estimated by EMCD and compared to implemented density functional theory (DFT) calculations, as illustrated in table 1. The influence of the magnetocrystalline anisotropy is locally demonstrated [5]. This work in particular illustrates the feasibility of the EMCD technique for in‐situ experiments, and proves its potential to explore the anisotropy of magnetic materials.