Magnetic structure of (SmMn2)-Sm-154(Ge0.9Si0.1)(2) as a function of temperature and pressure

Neutron scattering and AC susceptibility measurement have been made on isot opically enriched (SmMn2)-Sm-154(Ge0.9Si0.1)(2). A temperature versus press ure magnet:ic phase diagram is proposed. The incommensurate cone structures detected in SmMn2Ge2 at low temperatures and pressures do not appear in th e phase diagram of the Si-substituted system. There is no evidence of a cha nge in the magnetic structure associated with a small peak in susceptibilit y observed at around 145 K which has previously been interpreted in terms o f changes to the cone structure. However, as with SmMn2Ge2, the non-colline ar magnetic structures of these magnetic phases are such that a larger anti ferromagnetic component appears within (001) ab-planes in the ferromagnetic states than in the antiferromagnetic state. With increasing Si substitutio n, the antiferromagnetic phase becomes the magnetic equilibrium state over a wider temperature range. The observed changes in the Mn-Mn spacing and ma gnetic coupling are largely consistent with previous related observations, although under a pressure of similar to 8 kbar, low-temperature magnetic st ructures are found below the critical lattice spacing of a = 4.031 Angstrom which are similar to those observed at ambient pressure. (C) 2000 Elsevier Science B.V. All rights reserved.