Magnetic order and spin dynamics in substituted spinel Mg1-xMn2+xO4

We investigate the substituted spinel Mg1-xMn2+xO4, in five powder compositions 0 less than or equal to x less than or equal to 1, where divalent Mg is expected to occupy mainly the B spine] site. A zero-field precession is detected for all samples below an x-dependent ordering temperature, which is different from that detected by macroscopic magnetization. The precessing amplitude in the ordered phase displays temperature-dependent deviations from the canonical value of expected for our powder samples, indicating the presence of a radical state. The difference between the SQUID and the muSR-order temperatures is attributed to a collinear intermediate state stabilized by Mg. (C) 2002 Elsevier Science B.V. All rights reserved.