Room temperature positive exchange bias in CoFeB/D019-Mn3Ge noncollinear antiferromagnetic thin films

Polycrystalline and single crystal antiferromagnetic D019-Mn3Ge thin films were grown by magnetron sputtering on GaN (0001) and Pt (111) templates at different substrate temperatures. Later, a CoFeB layer was grown on top of the D019-Mn3Ge films at room temperature. Single crystal D019-Mn3Ge thin films, with high surface roughness, induced an increase of the coercivity of the CoFeB ultrathin films, meanwhile polycrystalline D019-Mn3Ge thin films, with uniaxial texture and low surface roughness, induced positive exchange bias at room temperature by cooling the sample under a magnetic field of 2 T. No exchange bias was observed with lower cooling magnetic fields. The non-zero magnetic moment of uncompensated D019-Mn3Ge grains of the textured films couple antiferromagnetically leading to positive exchange bias.