Oscillation of coercivity between positive and negative in MnxGe1-x：H ferromagnetic semiconductor films

Amorphous MnxGe1-x：H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co- sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1-x：H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1-x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6：H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1-x films for the application in spintronics.