Large Noncollinearity and Spin Reorientation in the Novel ${\mathrm{Mn}}_2\mathrm{RhSn}$ Heusler Magnet

Noncollinear magnets provide essential ingredients for the next generation memory technology. It is a new prospect for the Heusler materials, already well known due to the diverse range of other fundamental characteristics. Here, we present a combined experimental and theoretical study of novel noncollinear tetragonal ${\mathrm{Mn}}_2\mathrm{RhSn}$ Heusler material exhibiting unusually strong canting of its magnetic sublattices. It undergoes a spin-reorientation transition, induced by a temperature change and suppressed by an external magnetic field. Because of the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, ${\mathrm{Mn}}_2\mathrm{RhSn}$ is suggested to be a promising candidate for realizing the Skyrmion state in the Heusler family.

Figure 1

(a) Crystal and magnetic structures of ${\mathrm{Mn}}_{2}YZ$ Heusler compounds. Because of the magnetocrystalline anisotropy induced by the tetragonal distortion, the ${\mathrm{Mn}}_{\mathrm{I}}$ magnetic moments are oriented along the $c$ axis; the moments on ${\mathrm{Mn}}_{\mathrm{II}}$ are canted in an alternating manner with respect to the $c$ axis. (b) Schematic picture of the leading magnetic exchange interactions between different atomic layers in ${\mathrm{Mn}}_{2}YZ$ (atomic planes containing $Z$ and $Y$ elements are shown in blue and red, respectively). The arrows show the orientation of the spin moments on Mn, and the springs show the exchange interactions between different planes. Considering only the nearest antiparallel interactions $J$ (between ${\mathrm{Mn}}_{\mathrm{I}}\text{−}Z$ and ${\mathrm{Mn}}_{\mathrm{II}}\text{−}Y$ planes) leaves the magnetic structure collinear; introducing the next-nearest antiparallel coupling $j$ (between ${\mathrm{Mn}}_{\mathrm{II}}\text{−}Y$ planes) leads to the alternating canting of ${\mathrm{Mn}}_{\text{II}}$ moments by $\theta$ and $2\pi -\theta$.

Figure 2

(a) Temperature-dependent neutron diffraction spectra. The (002) peak decays over 1.8–80 K. (b) Weakening of the in-plane magnetism (produced by the ${\mathrm{Mn}}_{\mathrm{II}}$ $x$ component) releases the $z$ component of ${\mathrm{Mn}}_{\mathrm{I}}$, while the $z$ component of ${\mathrm{Mn}}_{\mathrm{II}}$ evolves rather insignificantly.

Figure 3

Evolution of the magnetic structure with the temperature. Canted (red regions), collinear ferrimagnetic (yellow regions), and disordered (blue regions) magnetic states of ${\mathrm{Mn}}_2\mathrm{RhSn}$. (a) Zero-field-cooled (ZFC), field-cooled (FC), and field-heated (FH) magnetization as a function of the temperature measured at induction fields of 0.1, 0.5, and 5 T. (b) Real (${\chi }^{\prime }$) and imaginary (${\chi }^{\prime \prime }$) ac-susceptibility components are frequency independent and show a pronounced step at the onset of the FiM phase. (c) The change in the canting angle occurs because of the simultaneous realignment of the ${\mathrm{Mn}}_{\mathrm{II}}$ moment and a decrease in its absolute value. This, in turn, releases the previously suppressed ${\mathrm{Mn}}_{\mathrm{I}}$ moment from $3.5{\mu }_B$ to $4.5{\mu }_B$. (d) The sum of the total and $z$ components of the ${\mathrm{Mn}}_{\mathrm{I}(\mathrm{II})}$ moments follow the ac-susceptibility behavior. No in-plane component is present after 80 K. (e) A change in the slope of the heat capacity curve is observed in the vicinity of the spin reorientation. (f) Evolution of the lattice parameters with temperature: the change in the magnetism is echoed mainly by the $c$ parameter, while $a$ evolves monotonically.