Tuning magnetostructural phase transition in CoMn$_{0.88}$Cu$_{0.12}$Ge by application of hydrostatic pressure

Structural and magnetic properties of the CoMn$_{0.88}$Cu$_{0.12}$Ge compound have been investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) accompanied with investigation of magnetic properties under applied hydrostatic pressure up to 12 kbar. It has been found that the orthorhombic crystal structure of the TiNiSi-type, which is dominant at low temperatures, turns into the hexagonal Ni$_2$In-type one, slightly above 200 K. The structural transition is of the first-order type as confirmed by presence of distinct thermal hysteresis exceeding 20 K. The ac magnetic measurements indicate a ferromagnetic order below the Curie temperature $T_C$ of 238 K, followed by additional anomaly at lower temperatures - the latter one being related to the structural transition. Application of hydrostatic pressure leads to temperature separation of the purely magnetic transition, whose Curie temperature $T_C$ slowly increases with applied pressure, and the magnetostructural transition characterized by critical temperature showing much rapid decrease with increasing pressure. Comparison of the DSC data for the investigated compound and the isostructural CoMn$_{0.95}$Cu$_{0.05}$Ge one has made it possible to determine both the structural and magnetic components of entropy change.