Magnetic ordering of the antiferromagnet from magnetization and neutron-scattering measurements

Abstract

Magnetization and neutron-diffraction measurements were performed on a single crystal of (Formula presented) This quartenary magnetic semiconductor has the stannite structure (derived from the zinc-blende structure which is common to many II-VI dilute magnetic semiconductors), and it orders antiferromagnetically at low temperature. The neutron data for the nuclear structure confirm that the space group is (Formula presented) Both the neutron and magnetization data give (Formula presented) K for the Néel temperature. The neutron data show a collinear antiferromagnetic (AF) structure with a propagation vector k=[1/2,0,1/2], in agreement with earlier neutron data on a powder. However, the deduced angle θ between the spin axis and the crystallographic (Formula presented) direction is between 6° and 16°, in contrast to the earlier value of 40°. The magnetization curve at (Formula presented) shows the presence of a spin rotation (analogous to a spin flop), which indicates that the spin axis is indeed close to the (Formula presented) direction. The deduced magnetic anisotropy gives an anisotropy field (Formula presented) kOe. At high magnetic fields the magnetization curve at (Formula presented) shows the transition between the canted (spin-flop) phase and the paramagnetic phase. The transition field, (Formula presented) kOe, yields an intersublattice exchange field (Formula presented)=124 kOe. The exchange constants deduced from (Formula presented) and the Curie-Weiss temperature Θ=-25 K show that the antiferromagnetic interactions are an order of magnitude smaller than in II-VI dilute magnetic semiconductors (DMS’s). The much weaker antiferromagnetic interactions are expected from the difference in the crystal structures (stannite versus zinc-blende). A more surprising result is that the exchange constant which controls the AF order below (Formula presented) is not between Mn ions with the smallest separation. This result contrasts with a prediction made for the related II-VI DMS, according to which the exchange constants decrease rapidly with distance. © 1997 The American Physical Society.