Static And Dynamic Magnetic Properties Of Half-metalic Heusler Alloy Co₂FeAl

Half-metalic Heusler alloy Co₂FeAl?CFA?has shown a remarkable potential application in spintronics due to its high spin-polarization and low damping parameters.In recent decades,many methods were used to fabricate Co₂FeAl thin films and spintronic devices based on Co₂FeAl.In this work,Co₂FeAl single-crystal thin films with different thickness were prepared by molecular beam epitaxy?MBE?.Static and dynamic magnetic measurements have been done to study the magnetic properties of the Co₂FeAl samples.The Co₂FeAl single-crystal thin films with different thickness were grown on Mg O?001?substrates using MBE method.The substrates were annealed at 773 K for 5 min for thermal cleaning the substrates preparing to growth.Then the Co₂FeAl films were grown under a substrate temperature of 473 K and a base pressure less than 1×10-9 mbar.The constituent of the three elements was modulated by the temperatures of the evaporator sources,and the thickness of the samples?26.4 nm,17.4 nm,8.9 nm,6.1 nm and 4.6 nm,respectively?was controlled by adjusting the growth time.In-situ reflection high-energy electron diffraction?RHEED?and high resolution X-ray diffraction were used to analysis the structure of the Co₂FeAl epitaxial films.The static and dynamic magnetic characteristics of the samples with variable thickness were revealed using vibrating sample magnetometer?VSM?,direct current?dc?transport measurement system and spin rectification measurement system.The results are as follows:?1?The RHEED and HRXRD results suggest a well epitaxial growth of the CFA films according to the CFA?001?[100][110]//Mg O?001?[110][100] epitaxial relation.The intergrated peak intensity ratio of the?002?peak and?004?peak verify a main lattice phase of B2 phase in the CFA films,which could show a half-metalic properties.?2?The saturation magnetization of CFA is independent with the thickness.The in-plane anisotropies of CFA would change from a cubic symmetry to a cubic symmetry combined with a uniaxial symmetry.The uniaxial anisotropy should attribute to the strain originate from the mismatch of the lattice constants between Mg O and CFA.?3?CFA films with all the thickness show a negative anisotropic magnetoresistance?AMR?ratio.It could be illustrated by the s?-d? electron scattering process,which is different from the s?-d? electron scattering process in conventional ferromagnetic metals.It is also a finger-point of half-metalic properties.?4?The angular dependence of the resonant fields shows a superposition of a cubic symmetry and a uniaxial symmetry given out by the in-plane rotation spin rectification measurement.The cubic anisotropy constant K4 and the uniaxial anisotropy constant K2 are obtained by fitting the resonant fields-angle characteristics with Smit-Beljes formula.The fitting results show an obvious decrease of K4 and an increase of K2 with the decrease of the thickness of the CFA films.?5?The line widths of these samples present a same angular dependence of the resonant fields.In further measurement the angular dependence of the line widths is demonstrated to be driven by the anisotropic effective damping constant,which is identified as isotropous.The anisotropy of effective damping constant is well illustrated while the two magneton scattering process has been taken into consideration.So we attribute the anisotropy of the effective damping constant of the CFA films to the two magneton scattering process.