Magnetic-field-modulated written bits in TbFeCo thin films: Transmission electron microscopy Lorentz and scanning electron microscopy with polarization analysis studies

Abstract

Domains written thermomagnetically in TbFeCo thin films are studied with Lorentz transmission electron microscopy (TEM) and scanning electron microscopy with polarization analysis (SEMPA). Four different rare-earth/transition-metal compositions TbxFeyCo1−x−y are examined. The domain structures observed with both techniques are similar even though TEM Lorentz only detects the transverse component of the net magnetic field along the electron’s trajectory through the sample, while SEMPA detects the surface electron-spin polarization (magnetization). We find that the magnetic contrast in the SEMPA measurements is proportional to the magnetization of the transition-metal (TM) subnetwork which is antiferromagnetically coupled to the rare-earth (RE) subnetwork. This allows high-contrast SEMPA images to be acquired even when the system is magnetically compensated (Ms=‖MRE−MTM‖=0). The surface magnetization can be explained by assuming that the surface of the TbFeCo alloy consists of an outermost thin oxide layer followed by an Fe-rich subsurface layer. The importance of the demagnetizing field on the switching and domain nucleation process for thermomagnetically written bits is examined.