Critical scattering of UNiGa

The hexagonal intermetallic compound UNiGa adopts the ZrNiAl structure type , orders antiferromagnetically below 39 K and exhibits several AF phases wi th lowering temperature. Within narrow temperature range 34 K - 39 K there exist four magnetic phase transitions in zero magnetic field. In all these phases the magnetic structure is highly anisotropic with magnetic moment pa rallel to the c-axis. The phase just below TN is an incommensurate antiferr omagnetic structure characterised by propagation vector q = (0, 0, q(z)), w here q(z) is in the range 0.36 - 0.37. We present results of magnetic criti cal scattering study on a UNiGa single crystal. The intensity of critical s cattering drops rapidly within a very narow temperature range above TN.