Microstructure and magnetic properties of FePt and Fe/FePt polycrystalline films with high coercivity

Abstract

We have investigated the microstructure and the magnetic properties of FePt and Fe/FePt polycrystalline thin films with high coercivity. The L10 FePt particulate film deposited on a heated amorphous SiO2 substrate showed a large coercivity (Hc) as high as 23 kOe. Contrary to an epitaxially grown single crystal FePt film, the Hc did not show a drastic decrease when the film morphology changed from particulate to continuous. The polycrystalline film with a thickness of 100 nm exhibited a coercivity of 13 kOe in spite of its simple processing route. This high coercivity is attributed to the magnetic domain pinning at the grain boundaries. By depositing Fe layers on the particulate FePt films, an increase of remanence and energy product was observed as a result of the exchange coupling of the Fe and FePt layers.

Nanostructured MnGa films on Si/SiO2 with 20.5 kOe room temperature coercivity

“…25 However, the still considerably large coercivity of the high-rate sample can be explained by the rough microstructure, grain boundaries, and other imperfections (e.g., nonmagnetic phases) which inevitably lead to considerable domain wall pinning. 26 As is typically found in hard magnetic systems, 1,5 the presence of non-magnetic or weakly magnetic phases is crucial for both strong domain wall pinning and magnetic separation of individual grains, both of which contribute to a large coercivity. Unfortunately, there is usually a trade-off between high coercivity and high saturation magnetization in such systems.…”

Effects of deposition temperature and in-situ annealing time on structure and magnetic properties of (001) orientation FePt films

“…It can be seen that the in-plane remanence is also progressively reduced with increasing deposition temperature, suggesting that increasing deposition temperature could enhance the perpendicular anisotropy of the film. The initial magnetization curves of all the films are convex downward and exhibit a critical field value after which the magnetization rapidly increases, which means that the initial magnetization curves have the characteristic of the rotation magnetization because a large magnetic field is required to magnetize the particles [22]. The hysteresis loops were also used to roughly evaluate the effective anisotropy constant expressed as Keff = HAMS/2, where HA is the anisotropy field which could be obtained by extrapolating the perpendicular and parallel hysteresis loops, and MS is the saturation magnetization [23].…”

Coercivity Control of FePt Nanoparticles by Interfacial Disorder

“…4) The average size of the larger particles is about 25 nm and that of the smaller particles is about 3 nm. Since the single domain size of the L1 0 FePt particle with a flat ellipsoidal shape is calculated to be approximately 200 nm, 5) all these particles are believed to be single domain ones. The selected area diffraction pattern in the inset shows that the FePt is L1 0 ordered and has the cube/cube orientation relationship with MgO.…”