µSR Study of the Dynamics of Internal Magnetic Correlations in Tb(Bi)MnO3 Multiferroic in Magnetically Ordered and Paramagnetic States

The dynamics of internal magnetic correlations in Tb0.95Bi0.05MnO3 multiferroic in the temperature range of 10–290 K has been studied. Separation into two phases with different relaxations of the polarization of muons in the basic matrix of the crystal and the phase separation regions has been detected for the first time both in a magnetically disordered state at T < TN = 40 K and in a paramagnetic state in a transverse magnetic field of 290 G in a temperature range of 80–150 K. A muon ferromagnetic complex (Mn3+-Mu-Mn4+), where the hyperfine interaction in a muonium depolarizes a muon in a time less than 10−8 s, is formed at T < 40 K in phase separation regions containing pairs of Mn3+ and Mn4+ ions, as well as electrons that recharge them. In the matrix of the original crystal containing only Mn3+ ions, a muonium is formed with a broken hyperfine bond. In this case, muons are depolarized at a high rate because of their interactions with the local magnetic fields of a cycloid. At temperatures of 80–150 K, one phase in the phase separation regions constitutes approximately 50% and is characterized by long relaxation times about 10 µs (described by the Gaussian relaxation function). The other phase is formed by Mn3+-Mn3+ correlations in the short-range magnetic order regions in the matrix of the original crystal, which are weakly sensitive to a magnetic field of 290 G.