Low-Field Microwave Absoption and its Corelation with Magnetization in Ni-Mn-Sn Heusler Alloy Films

Ferromagnetic as resonance (FMR) is associated with the resonance absorption of microwaves by ferromagnetic materials at an appropriate magnetic field. Analysis of FMR signal gives information about effective magnetization, effective magnetic anisotropy, damping constant, spin splitting g factor, magnetic inhomogeneity etc. of a material. Recently, a new non resonant microwave absorption phenomenon at low or zero magnetic field called low-field microwave absorption (LFMA) has been observed in some materials. Unlike the resonant FMR absorption, Non resonant LFMA shows a hysteresis behavior between in the spectrum recorded during increasing and decreasing magnetic field. LFMA has been observed in high temperature superconductors [1], amorphous ribbons [2], glass coated micro wires [3], ferrite nanoparticles [4], magnetic thin film [5], etc. Though several interpretations and explanations have been proposed for the origin of LFMA signal, it is still not properly understood and the absence of LFMA various materials is unexplained. In this paper, we report for the first time, the detection of LFMA signal in polycrystalline Ni-Mn-Sn thin films deposited on Si substrates. This discovery of LFMA in Heusler alloys films offers an opportunity to explore the properties of LFMA and its universality in Heusler alloys films LFMA measurements were performed on the films at from temperature at 9.44 GHz using an ESR spectrometer. LFMA spectra were recorded with different orientations film plane with respect to applied field direction (θH) staring from 0° to 90°. The LFMA hysteresis characteristics could be correlated with the isothermal magnetization (M-H) loop characteristics recorded for different film orientation in static magnetic measurements (cf. Fig. 1). When magnetic elements such as Fe, Co were substituted in Ni-Mn-Sn film, both LFMA signal as well as the M-H loop properties of the quaternary films varied in a correlated manner with substitution, signifying a strong dependence of LFMA on the magnetization process in these films. Apart from establishing LFMA in ternary and quaternary Ni-Mn-Sn Heusler alloy films, this study also points out that Ni-Mn-Sn thin films on Si substrate are potential candidates for fabricating low magnetic field sensors in microwave frequency range.