Probing magnetoelastic effects of ultrathin antiferromagnets via magnetic domain imaging in ferromagnetic-antiferromagnetic bilayers

We report an experimental investigation of the magnetoelastic effects of ultrathin antiferromagnets, performed by comparing the characteristic behavior of the induced spin-reorientation transition (SRT) of Co films in two types of epitaxially grown bilayers: face-centered-cubic (fcc)-like Mn/Co (fcc-Mn: a=3.75Å,c=3.76Å) and face-centered-tetragonal (fct)-Mn (a=3.61Å,c=3.78Å). Magnetic hysteresis loops and magnetic domain images indicate that both fcc-Mn and fct-Mn films can produce a (110) to (100) SRT in adjacent Co films when the thickness of the Mn layer is greater than a temperature-dependent critical value. Detailed analysis of the critical thickness of Mn films and the evolution of the Co domain structure upon SRT indicate that the fct-Mn film had a higher antiferromagnetic ordering temperature and stronger lateral Mn-Mn exchange coupling compared with the fcc-Mn film. The enhanced long-range antiferromagnetic ordering emerging concurrently with the in-plane lattice variation of the fcc-like Mn film in Mn/Co bilayers clearly showed the magnetoelastic effect of ultrathin antiferromagnets.