NMR study of successive magnetic transitions in the A-site ordered perovskite LaMn 3 Cr 4 O 12

We have investigated the successive magnetic phase transitions of the A-site ordered perovskite LaMn 3 Cr 4 O 12 by measuring 139 La nuclear magnetic resonance (NMR) spectra. The successive magnetic transitions are revealed by a very small but clear increase in the full width at half maximum (FWHM) of the 139 La NMR signal at T M2 = 150 K and by the disappearance of the signal due to the line broadening at temperatures below T M1 = 50 K. These two magnetic transitions are associated with independent orderings within the Cr-site sublattice at T M2 and within the Mn-site sublattice at T M1 . Regarding the magnetic structure of the Cr-site sublattice at temperatures below T M2 , the cancellation of internal fields at the La site, ruling out ferromagnetic and multi- q antiferromagnetic structures, is consistent with the typical antiferromagnetic structure for perovskites, such as G-, A- and C-type orders. The uncanceled internal field at the La site at temperatures below T M1 is also consistent with these typical antiferromagnetic structures in the Mn-site sublattice. The differences in the temperature dependences of the Knight shift K ( T ) and the bulk susceptibility χ ( T ) are consistently explained by the independent magnetic orderings of the Cr- and the Mn-site sublattices and the cancellation of internal field originating from the Cr-site sublattice at the La site at temperatures below T M2 .