Concentrational commensurate--incommensurate magnetic phase transition in [Y.sub.1 - x][Tb.sub.x][Mn.sub.6][Sn.sub.6]

The magnetic state of [Y.sub.1 - x][Tb.sub.x][Mn.sub.6][Sn.sub.6] (with x ≤ 0.25) alloy is studied at different temperatures and magnetic fields by neutron diffraction. The alloy with [x.sub.c] = 0.22 exhibits an incommensurate-to-commensurate structure phase transition. The transition is accompanied by a decrease in the unit- cell volume. The weak dependence of the intensity of satellites on the x concentration and the monotonic displacement of their angular positions with increasing x allow us to conclude that the antiferromagnet → ferrimagnet transition occurs through the uniform magnetic state. The incommensurate phase in Y[Mn.sub.6][Sn.sub.6] exhibits four satellites, which are observed in the low-angle range of X-ray diffraction pattern and demonstrate different behavior with changing temperature. At 293 K, the antiferromagnet → ferromagnet transition in the [Y.sub.1 - x][Tb.sub.x][Mn.sub.6][Sn.sub.6] compound can be induced by applied magnetic field, in particular, the field [μ.sub.0]H = 0.3 T induces the transition in [Tb.sub.0.15][Y.sub.0.85][Mn.sub.6][Sn.sub.6]. Keywords: magnetic phase transitions, neutron diffraction, intermetallic compounds DOI: 10.1134/S0031918X13070028