Magnetic phase transitions in UNi2Si2

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Abstract
We report neutron diffraction measurements on a single crystal of UNi2 Si2. Three magnetically ordering phases are observed below 123 K with the magnetic moment parallel to the c-axis in all three phases. The low temperature (T<53 K) phase is a superposition of a commensurate spin density wave with wave vector q = (0 0 0.667±0.002) and a ferromagnetic ordered moment of 1.1±0.3μB, the intermediate (53 K<T<103 K) is a simple body-centered tetragonal antiferromagnet with an ordered magnetic moment of 1.8±0.2μB and the high-temperature phase is an incommensurate spin density wave with wave vector q = (0 0 0.744±0.002) at 110 K. The phase transitions at 53 and 103 K are first order.