Direct measurement of the magnetic anisotropy field in Mn–Ga and Mn–Co–Ga Heusler films

The static and dynamic magnetic properties of tetragonally distorted Mn–Ga based alloys were investigated. Static properties are determined in magnetic fields up to 6.5 T using SQUID magnetometry. For the pure Mn_1.6Ga film, the saturation magnetisation is 0.36 MA m⁻¹ and the coercivity is 0.29 T. Partial substitution of Mn by Co results in Mn_2.6Co_0.3Ga_1.1. The saturation magnetisation of those films drops to 0.2 MA m⁻¹ and the coercivity is increased to 1 T.The time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the high-frequency dynamics of Mn–Ga. The ferromagnetic resonance frequency extrapolated to zero-field is found to be 125 GHz with a Gilbert damping, α, of 0.019. The anisotropy field is determined from both SQUID and TR-MOKE to be 4.5 T, corresponding to an effective anisotropy density of 0.81 MJ m⁻³.Given the large anisotropy field of the Mn_2.6Co_0.3Ga_1.1 film, pulsed magnetic fields up to 60 T are used to determine the field strength required to saturate the film in the plane. For this, the extraordinary Hall effect was employed as a probe of the local magnetisation. By integrating the reconstructed in-plane magnetisation curve, the effective anisotropy energy density for Mn_2.6Co_0.3Ga_1.1 is determined to be 1.23 MJ m⁻³. (paper)