Structure and magnetization reversal mechanism in L10 FePt films with perpendicular magnetic anisotropy

A series of L10 Fe63Pt37 films with controlled thickness (tFM) were deposited on MgO(100) substrates for microstructure and magnetization reversal mechanism study. X-ray diffraction measurements show that face-centered tetragonal (200) peak also exists in addition to face-centered tetragonal (002) one, and becomes weak for thick films. High resolution electron microscopy study reveals the existence of periodic misfit dislocations at the FePt/MgO interface and other types of defects such as twins and antiphase boundary inside the film. Out-of-plane initial magnetization shows a slow increase responding to the external magnetic field and then follows a steep increase. The out-of-plane coercivity HC at room temperature decreases with increasing tFM and increases when the angle θH between the external magnetic field and the film normal direction increases. HC at θH = 0 changes as a linear function of temperature for individual samples and the slope decreases with increasing tFM. In addition, magnetic viscosity measurements show that the fluctuation field at room temperature decreases with increasing tFM. These phenomena indicate that the magnetization reversal in the L10 FePt films should be realized by the motion of weakly pinned domain wall and thus governed by the thermal activation model. The magnetization reversal thermal activation volume and corresponding energy increase with increasing tFM, as a result of the interactions between domain walls and structural defects can be attributed to the sample microstructural characteristic evolution with tFM.

► A series of L10 Fe63Pt37 films with controlled thickness (tFM) were prepared. ► Periodic misfit dislocations are observed at the FePt/MgO interface. ► The dependence of HC on tFM and T is determined by the evolution of microstructure. ► The critical pinning field is determined by interface defects. ► The thermal activation energy is determined by both interface and film defects.