Thermal expansion and magnetostriction of UNiGa single crystal have been measured at the range of pressures up to 2.2 GPa and magnetic fields up to 1.5T. The results are reported with a special emphasis on anomalies accompanying the magnetic phase transitions and the effect of pressure on the critical parameters (transition temperature and magnetic field). Formation of a new antiferromagnetic phase induced by pressures above 1.8 GPa is revealed. Analysis of results enabled us to construct P-T magnetic phase diagrams for fields up to 1.5T. The magnetoelastic effects are discussed in terms of marked variations in electronic structure accompanying transitions between different magnetic structures with various couplings of U magnetic moments along the c-axis and involvement of strong spin-orbit interaction.
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