Broadband ferromagnetic resonance in Ni-Mn-Ga single crystal

We present a broadband ferromagnetic resonance study in single crystalline Ni₅₀Mn_28.1Ga_21.9 in the temperature range from room temperature to 120 °C in which the transformation from martensite to austenite phase takes place. Our measurements demonstrate that a large change (an order of magnitude) in the magnetocrystalline anisotropy at the martensitic phase transformation results in a sharp change of the resonance magnetic field. In a single variant martensite phase, the resonance fields satisfy the Kittel’s resonance condition for a thin film with the gyromagnetic factor g = 2.0. With the magnetic field parallel to the easy c-axis of the single variant martensite, the resonance is observed only for frequencies larger than 22 GHz. For the multivariant martensite case, the magnetic coupling between the twin variants can be taken into account for the satisfactory Kittel’s fit. We observe a weak magnetocrystalline anisotropy in the austenite phase, just above the reverse martensite transformation, comparable to the previous reports based on different magnetic measurements.