Magnetic Phase Diagram and Field Induced Magnetic Structure in DyCo2Si2

The H - T magnetic phase diagram and field induced magnetic structure in tetragonal DyCo 2 Si 2 with a two-step metamagnetic process have been determined by magnetization and neutron diffraction experiments using a single crystal as well as specific heat experiment on a polycrystalline sample. Three magnetic phases exist below T N =23 K. A simple antiferromagnetic structure (phase I), with the propagation vector Q 1 =(0, 0, 1) and moments along the c -axis, is stable below 21 K under low field. The intermediate field induced magnetic structure (phase II) is characterized by two additional propagation vectors: i) Q 0 =(0, 0, 0) and ii) Q 2 =(1/2, 1/2, 1/2) which is a sub-harmonics of (1, 1, 1) (≡ Q 1 ) and consists of ferromagnetic (111) planes with the sequence of + + + -. It has a resultant magnetization of half the saturation value, i.e. 5.0 µ B /f.u., at low temperature. Between T N and 21 K, an antiferromagnetic phase (phase III) with an unknown structure appears.