Exchange anisotropy in Fe-MnF2 nanogranular films

This paper reports on the magnetic properties of granular films consisting of iron, a ferromagnetic metal, and an insulator MnF₂, which is antiferromagnetic below the Neel temperature T_N = 67 K. Films were prepared by co-evaporation in vacuum and deposited onto polyimide films. DC magnetization curves recorded by a PPMS magnetometer from 5 to 300 K. Magnetization measurements for the sample with x = 0.25 showed superparamagnetic behavior at 300 K. The sample with x = 0.50 was soft ferromagnetic with the coercive field H_c = 20 Oe at 300 K. X-ray diffraction and Mossbauer spectroscopy were utilized for the characterization of the samples. Above T_N, strong ferromagnetic exchange coupling between Fe and MnF₂ is dominant. Below T_N, each iron particle is magnetized in a random direction as determined by the magnetic anisotropy.