On the influence of nanometer-thin antiferromagnetic surface layer on ferromagnetic CrO ₂

We investigate the influence of naturally grown 2-5 nm thin surface layer of antiferromagnetic (AFM) Cr ₂O ₃ on the half metallic ferromagnet CrO ₂ by measuring the magnetic behavior of a single micro-crystal. The temperature variation of the magnetic stray fields of the micro-crystal measured by micro-Hall magnetometry shows an anomalous increase below ∼ 60 K. We find clear evidence that this behavior is due to the influence of the AFM surface layer. The average amplitude of the Barkahausen jumps exhibits a similar temperature dependence indicating that the AFM surface layer plays a role in defining the potential landscape seen by the domain configuration in the ferromagnetic grain.