RESUMO
The demagnetization and associated magnetocaloric effect (MCE) in strong-weak-strong ferromagnetic trilayers, upon a reorientation of the strong ferromagnets from parallel to antiparallel (AP) magnetization, is simulated using atomistic spin dynamics. The simulations yield non-trivial spin distributions in the AP state, which in turn allows entropy to be calculated directly. The influence of longer-range spin-spin interactions and of variable strength of the external switching field are investigated. Finally, we find that the MCE in the system can be significantly improved by allowing the local exchange to vary through the spacer, which in practice can be implemented by spatially tailoring the spacer's magnetic dilution.
RESUMO
Ferromagnetic resonance properties of F1/f/F2/AF multilayers, where weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic layers F1 and F2, with F1 being magnetically soft and F2-magnetically hard due to exchange pinning to antiferromagnetic layer AF, are investigated. Spacer-mediated exchange coupling is shown to strongly affect the resonance fields of both F1 and F2 layers. Our theoretical calculations as well as measurements show that the key magnetic parameters of the spacer, which govern the ferromagnetic resonance in F1/f/F2/AF, are the magnetic exchange length (Λ), effective saturation magnetization at T = 0 (m0) and effective Curie temperature (T(C)(eff)). The values of these key parameters are deduced from the experimental data for multilayers with f = Ni(x)Cu(100-x), for the key ranges in the Ni-concentration (x = 54 ÷ 70 at. %) and spacer thickness (d = 3 ÷ 6 nm). The results obtained provide a deeper insight into thermally-controlled spin precession and switching in magnetic nanostructures, with potential applications in spin-based oscillators and memory devices.
RESUMO
Polycrystalline (Co2Fe)(x)Ge(1-x) Heusler alloy films are fabricated by sputtering on amorphous substrates and shown to possess three types of magnetic anisotropy. The nearly stoichiometric composition of x = 50 m.f.% shows a rectangular hysteresis loop and isotropic coercive and ferromagnetic resonance fields when the film is field-magnetized along any in-plane direction, thus predominantly possessing rotatable in-plane magnetic anisotropy. Higher-x compositions show evidence of two- and fourfold in-plane anisotropy superposed on the rotatable one. A qualitative model of the observed anisotropic magnetic properties is proposed. The model explains the rotatable anisotropy by taking into account dry friction for the in-plane rotation of the magnetization direction in a fine-grained polycrystalline film with the magnetic grain size smaller than the correlation length of the inter-grain exchange interaction. The observed two- and fourfold magnetic anisotropy contributions are attributed to partial texturing of the fine-grained films, even though the films are grown on amorphous SiO2 substrates. These results should be valuable for understanding and controlling the magnetic behaviour of highly spin-polarized Heusler alloy films used in various magnetic nanodevices.