Microstructures and Interface Magnetic Moments in Mn(2)VAl/Fe Layered Films Showing Exchange Bias

Heusler alloys are a material class exhibiting various magnetic properties, including antiferromagnetism. A typical application of antiferromagnets is exchange bias that is a shift of the magnetization curve observed in a layered structure consisting of antiferromagnetic and ferromagnetic films. In this study, a layered sample consisting of a Heusler alloy, Mn [Formula: see text] VAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered Mn [Formula: see text] VAl is known as a ferrimagnet, with an optimum fabrication condition for the Mn [Formula: see text] VAl layer, the Mn [Formula: see text] VAl/Fe layered structure exhibits exchange bias. The appearance of the antiferromagnetic property in the Mn [Formula: see text] VAl is remarkable; however, the details have been unclear. To clarify the microscopic aspects on the crystal structures and magnetic moments around the Mn [Formula: see text] VAl/Fe interface, cross-sectional scanning transmission electron microscope (STEM) observation, and synchrotron soft X-ray magnetic circular dichroism (XMCD) measurements were employed. The high-angle annular dark-field STEM images demonstrated clusters of Mn [Formula: see text] VAl with the L2 [Formula: see text] phase distributed only around the interface to the Fe layer in the sample showing the exchange bias. Furthermore, antiferromagnetic coupling between the Mn- and Fe-moments were observed in element-specific hysteresis loops measured using the XMCD. The locally ordered L2 [Formula: see text] phase and antiferromagnetic Mn-moments in the Mn [Formula: see text] VAl were suggested as important factors for the exchange bias.