Magnetic phase transitions in Heusler compounds Fe3-xMnxSi

Fe3-xMnxSi has been studied for a long time because of its unusual magnetic properties and complex magnetic phase diagrams. Fe3-xMnxSi (0.7 < x < 1.7) was known to exhibit a ferromagnetic transition, and at a lower temperature another transition to a phase with antiferromagnetic components. Recently we found that when x=1.7 another antiferromagnetic transition occurs at an even lower temperature, that is, there are three magnetic transitions. The two antiferromagnetic transition temperatures have different dependence on magnetic field. Therefore, these phases possibly have unusual magnetic structures and properties, as observed in other Mn-based antiferromagnetic compounds. In this study we will investigate the nature of the transitions and the magnetic phases using muSR measurements. This will reveal peculiar properties of the transitions and antiferromagnetic phases.