MAGNETIC PHASE-TRANSITION IN DYNI2SI2

Magnetic ordering and magnetic phase transition in DyNi2Si2 have been studied by neutron diffraction measurements on powder and single cryst al specimens. This compound has an order-to-order phase transition at about 3.5 K, below under the Neel temperature. Experimental results in dicated that the phase transition is a first-order transition from a c ommensurate square-wave type modulation in the c-plane with the two-di mensional propagation vectors k = (1/2 +/- tau, 1/2 -/+ tau, 0) with t au = 0.125 = 1/8 just below T(N) to a sine-wave type structure with ta u = 0.132 which is incommensurate with the lattice periodicity.