Magnetic and magnetoelastic properties of antiferromagnet FeGe2

The magnetic susceptibility chi of single-crystal antiferromagnet FeGe2 (T-N=289 K) was measured in the temperature range from 4.2 to 300 K in a magnetic field H up to 40 kOe applied along the main crystallographic axes. For the antiferromagnetic (AFM) state at low temperatures, a strong increase in chi is observed with increasing H applied along the [100] axis, which reaches saturation at H >= H-0 similar to 11 kOe. It is assumed that this behavior is associated with a field-induced change in the AFM domain structure, and the single-domain state is realized in a field above H-0 with the AFM axis perpendicular to the field direction. The study of chi under the uniaxial P-a and uniform P pressures in a wide temperature range has revealed an anomalously large increase in x in AFM state with increasing uniaxial pressure for P-a||H||[100] at H << H-0. The observed growth of chi saturates at pressure P-a >= P-a* similar or equal to 1.5 kbar and suggests the formation of the single-domain state for the above conditions. The values of uniform pressure effect on chi was found to lie in the range d ln chi/dP=- (2-3) Mbar(-1), being weakly dependent on the magnetic state and field direction. In addition, the uniform pressure effect on the transition temperature between two AFM structures in FeGe2, T-M similar or equal to 263 K, was found to be weak.