Nuclear magnetic resonance in noncollinear antiferromagnet Mn3Al2Ge3O12

The 55Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice antiferromagnet Mn3Al2Ge3O12 has been studied in the frequency range of 200–640 MHz in the external magnetic field H ‖ [001] at T = 1.2 K. Three absorption lines have been observed in fields less than the field of the reorientation transition Hc at the polarization h ‖ H of the rf field. Two lines have been observed at H > Hc and h ⊥ H. The spectral parameters indicate that the magnetic structure of manganese garnet differs slightly from the exchange triangular 120-degree structure. The anisotropy of the spin reduction and (or) weak antiferromagnetism that are allowed by the crystal symmetry lead to the difference of ≈3% in the magnetization of sublattices in the field H < Hc. When the spin plane rotates from the orientation perpendicular to the C3 axis to the orientation perpendicular to the C4 axis, all magnetic moments of the electronic subsystem decrease by ≈2% from the average value in the zero field.