規則格子マンガン酸化物の相分離およびスピン・電荷・軌道整列の核磁気共鳴およびμSR による研究

Nuclear magnetic resonance and μSR measurements have been made to study the phase separation,
spin, charge and orbital ordering in A-site ordered manganese oxides. In the antiferromagnetic
YBaMn2O6, the magnetic moments of Mn4+ and Mn3+ ions are estimated to be 3.0 μB and 3.6 μB
from the observed NMR spectra at 295 MHz and 320 MHz, respectively, which agree with the expected
spins S=3/2 and S=2 of Mn4+ and Mn3+ ions, respectively. In the μSR experimental results in
YBaMn2O6, the intensity of positrons shows the typical time decay of a single exponential function in
the paramagnetic phase and the oscillation in the antiferromagnetic phase, which indicates that the
antiferromagnetic phase in YBaMn2O6 is similar to the ordinary antiferromagnetic phase. 55Mn NMR
spectra in LaBaMn2O6 at low temperature consists of the signals from both ferromagnetic and
antiferromagnetic phases, which gives the evidence for the coexistence of the ferromagnetic and
antiferromagnetic phases in the ground state in LaBaMn2O6 from the microscopic point of view. In the
μSR experimental results in LaBaMn2O6, the intensity of positrons shows the typical time decay of a
single exponential function in the paramagnetic phase but still shows no oscillation in the ferromagnetic
phase, which indicates that the ferromagnetic phase in LaBaMn2O6 is very different from the ordinary
ferromagnetic phase. On the contrary, in the coexisting antiferromagnetic phase in the ground state the
intensity of positrons shows the typical time decay of oscillation due to the internal field, which
indicates that the coexisting antiferromagnetic phase in LaBaMn2O6 is similar to the ordinary
antiferromagnetic phase. These results may be concerned with the fact that the antiferromagnetic phase
is created in the ferromagnetic phase.