Abstract
Static magnetism and thermally activated magnetic relaxation were investigated in granular FePt films (20 nm-200 nm thick) with random magnetic anisotropy through hysteresis loop, torque curve and magnetization time dependence measurements. While the magnetism of thicker film (200 nm thick) is dominated by a single switching of the ordered L10 phase, thinner film (20 nm) displays a double switching, which is indicative of the presence of the disordered cubic phase. The pronounced behavior of double switching in thinner film suggests that the film grain boundary is composed of soft cubic magnetic phase. The magnetic relaxation study reveals that magnetic viscosity S of the films is strongly dependent on the external applied field and exhibits a maximum value (12 kAm) around the switching field and a vanishing behavior at low (1 kOe) and large (12 kOe) fields. The activation volume of the thermal switching was found to be much smaller than the physical volume of the granular structure due to the incoherent rotation mode of the magnetization reversal mechanism, which is established to be domain wall nucleation.
Highlights
In contrast to soft magnets suited for sensors and actuators applications,[1,2] hard magnetic materials are required for data storage and permanent magnets technologies
The hard magnetic character is conferred to materials through large uniaxial anisotropy, which is stabilized under low crystal symmetry such as tetragonal[3] and hexagonal
We present a detailed study about the thermal switching and the magnetization reversal process in granular L10 FePt films
Summary
In contrast to soft magnets suited for sensors and actuators applications,[1,2] hard magnetic materials are required for data storage and permanent magnets technologies. (4) The switching of the magnetization in the red curve from the positive to the negative states takes place in a narrow field range 7-9.5 kOe and the reversal mechanism is initiated through the nucleation field Hn (singularity point of the loop) which represents the lowest field to trigger magnetic instabilities in the film.
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