Magnetovolume effect in ${\mathrm{Mn}}_3{\mathrm{Cu}}_{1-x}{\mathrm{Ge}}_x\mathrm{N}$ related to the magnetic structure: Neutron powder diffraction measurements

Magnetic structures in an antiperovskite system, ${\mathrm{Mn}}_3{\mathrm{Cu}}_{1-x}{\mathrm{Ge}}_x\mathrm{N}$, with a large magnetovolume effect above $x=0.15$ have been studied by neutron powder diffraction measurement. The present neutron study revealed that not only a cubic crystal structure but also a ${\Gamma }^{5g}$ antiferromagnetic spin structure are key ingredients of the large magnetovolume effect in this itinerant electron system. The large magnetovolume effect is possibly ascribed to the geometrical frustration originating from the corner-shared octahedra of the antiperovskite structure.

Figure 1

Neutron powder diffraction patterns of (a) ${\mathrm{Mn}}_3\mathrm{Cu}\mathrm{N}$, (b) ${\mathrm{Mn}}_3{\mathrm{Cu}}_{0.85}{\mathrm{Ge}}_{0.15}\mathrm{N}$, and (c) ${\mathrm{Mn}}_3{\mathrm{Cu}}_{0.5}{\mathrm{Ge}}_{0.5}\mathrm{N}$ above and below magnetic ordering temperatures, which are at $T=300$ and $7\mathrm{K}$ for (a) and (b) and at $T=400$ and $15\mathrm{K}$ for (c), respectively.

Figure 2

(a) $T$ dependence of magnetic peak intensity of ${\mathrm{Mn}}_3{\mathrm{Cu}}_{1-x}{\mathrm{Ge}}_x\mathrm{N}$. Open circles denote the $\frac{1}{2}$ $\frac{1}{2}$ 0 peak for $x=0$. Closed triangles, open triangles, and closed circles denote the 1 0 0 peak for $x=0.15$, 0.2, and 0.5, respectively. (b) $T$ dependence of lattice constants of ${\mathrm{Mn}}_3{\mathrm{Cu}}_{1-x}{\mathrm{Ge}}_x\mathrm{N}$. At $x=0$, the average lattice constant is shown below the structural phase transition temperature $\left(143\mathrm{K}\right)$.

Figure 3

(a) Magnetic structure of ${\mathrm{Mn}}_3\mathrm{Cu}\mathrm{N}$. (b) ${\Gamma }^{4g}$ type antiferromagnetic cubic structure. (c) ${\Gamma }^{5g}$ type antiferromagnetic cubic structure. Cu , Ge, and N atoms are omitted for simplicity.

Figure 4

(a) Phase diagram of ${\mathrm{Mn}}_3{\mathrm{Cu}}_{1-x}{\mathrm{Ge}}_x\mathrm{N}$. Open and closed circles denote Curie and Néel temperatures determined from magnetization measurements in Ref. 19 and neutron measurements, respectively. The MVE was observed in the hatched $x$ range.