Ratio of 4:1 between ZnGeAs₂and MnAs phases in a single composite and its impact on the structure-driven...

A strong influence of the lattice degree of freedom on magnetoresistance (MR) under high pressure underlies the conception of 'structure-driven' magnetoresistance (SDMR). In most magnetic or topological materials, the suppression of MR with increasing pressure is a general trend, while for some magnetic composites the MR enhances and even shows unusual behavior as a consequence of structural transition. Here we investigated the SDMR in the composite material based on the ZnGeAs₂semiconductor matrix and MnAs magnetic inclusions in a phase ratio of 4:1. At ambient pressure, its magnetic and transport properties are governed by MnAs inclusions, i.e. it shows a Curie temperatureT_C≈ 320 K and metallic-like conductivity. Under high pressure, the low-field room temperature MR undergoes multiple changes in the pressure range up to 7.2 GPa. The structural transition in the ZnGeAs₂matrix has been found at ∼6 GPa, slightly lower than in the pure ZnGeAs₂(6.2 GPa). The huge SDMR as high as 85% at 6.8 GPa and 2.5 kOe, which contains both positive and negative MR components, is accompanied by a pressure-induced metallic-like-to-semiconductor-like transition and the enhanced ferromagnetic order of MnAs inclusions. This observation offers a competing mechanism between the robust extrinsic ferromagnetism and high-pressure electronic properties of ZnGeAs₂.