Magnetic anisotropy of single-crystal antiperovskite ${\mathrm{Mn}}_3\mathrm{GaC}$ studied by ferromagnetic resonance and dynamic magnetic-response simulations

The Mn-based antiperovskite ${\mathrm{Mn}}_3\mathrm{GaC}$ is an interesting material for magnetocaloric cooling applications below room temperature. To optimize its use, knowledge of the anisotropic magnetic properties is required. Here, we use a single crystal to study the magnetic anisotropy by the ferromagnetic resonance technique and magnetic-response simulations. The anisotropy constant $K_4=-5.49\mathrm{kJ}/{\mathrm{m}}^3$ obtained in combination from experiment and simulations is about an order of magnitude smaller than that of bcc Fe. The magnetically soft nature of this material practically in all crystallographic directions is favorable for using it in polycrystalline form for magnetic refrigeration.

Figure 1

Characterization of the crystal. (a) SEM image of the surface of the ${\mathrm{Mn}}_3\mathrm{GaC}$ crystal. The green frame shows the area of the EBSD analysis in (b). (b) $120\times 60\mu {\text{m}}^2$ EBSD grid with $0.08\mu {\mathrm{m}}^2$ resolution. The color-code corresponds to the identified phases given in the legend. (c) EBSD grid for crystal orientation. The uniform violet-colored region indicates constant Euler angles so that the crystal surface is determined to be a (100) plane after taking into account the tilt of the surface with respect to the detector. The color code of the Euler angles and crystal orientation directions corresponds to the representation used in Ref. [21]. The crystal is represented by the cube in the legend.

Figure 2

SEM images showing (a) the truncated prismatic ${\mathrm{Mn}}_3\mathrm{GaC}$ single crystal with {100} main surfaces. Small pieces of a Ga-rich phase are found mainly at the edges. (b) EDX mapping for the Mn $K\alpha 1$ (red) and (c) Ga $K\alpha 1$ emissions (green).

Figure 3

$M\left(T\right)$ of ${\mathrm{Mn}}_3\mathrm{GaC}$ single crystal in a field of 50 mT (red) and 2 T (black). Dashed blue lines mark the temperatures at which angular-dependent FMR spectra are measured.

Figure 4

Field dependence of the FMR absorption derivative. (a) The raw data at 140 K including features related to the presence of the ${\mathrm{Mn}}_2{\mathrm{Ga}}_5$ impurity phase and a strong ESR line at 0.332 T ranging beyond the vertical scale. The strong ESR line is mainly due to the carbon tape used for sample-mounting. There is no FMR related to ${\text{Mn}}_3\mathrm{GaC}$ at 140 K since it is AF at this temperature. (b) The FMR absorption derivative for different temperatures around $T_i=163\mathrm{K}$ at $0^{\circ }$. All spectra are subtracted from the 140 K spectra in part (a) to eliminate the ESR and background signals.

Figure 5

Angular dependence of FMR. (a) Angular dependence of FMR absorption derivative in gray scale measured at 200 K in the FM state. Parts (i)–(iv) show the orientation of the faces of the crystal and the orientation of the cell for the characteristic rotation angles $0^{\circ },{68}^{\circ },{130}^{\circ }$, and ${170}^{\circ }$. The selected coordinate system for the experimental geometry is included in (i)–(iv). (b) Calculated angular dependence of the amplitude of ${\widehat{e}}_{\varphi }^{\vec{M}}·\underline{\underline{\chi }}·{\widehat{e}}_{\varphi }^{\vec{B}}$ in gray scale. The simulated data are shifted by ${18}^{\circ }$ to comply with the initial orientation of the sample in the spectrometer shown in part (a), (i).