Magnetic structure of as a function of temperature and pressure

Neutron scattering and AC susceptibility measurements have been made on isotopically enriched 154 SmMn 2 ( Ge 0.9 Si 0.1 ) 2 . A temperature versus pressure magnetic phase diagram is proposed. The incommensurate cone structures detected in SmMn2Ge2 at low temperatures and pressures do not appear in the phase diagram of the Si-substituted system. There is no evidence of a change in the magnetic structure associated with a small peak in susceptibility observed at around 145 K which has previously been interpreted in terms of changes to the cone structure. However, as with SmMn2Ge2, the non-collinear magnetic structures of these magnetic phases are such that a larger antiferromagnetic component appears within (0 0 1) ab -planes in the ferromagnetic states than in the antiferromagnetic state. With increasing Si substitution, the antiferromagnetic phase becomes the magnetic equilibrium state over a wider temperature range. The observed changes in the Mn–Mn spacing and magnetic coupling are largely consistent with previous related observations, although under a pressure of ∼8 kbar, low-temperature magnetic structures are found below the critical lattice spacing of a =4.031 A which are similar to those observed at ambient pressure.