Changes of spin dynamics in multiferroic Tb1-xCaxMnO3

We report the results of a series of pSR measurements performed on polycrystalline and single crystalline Tb1-xCaxMnO3, with x = 0, 0.05 and 0.1. Analysis of the data indicates that the Neel transition temperature around 40 K for the undoped sample is in agreement with the previous result obtained by susceptibility measurement. We further find a peculiar behavior related to the relaxor ferroelectric of magnetic origin for 5% Ca doping. This type of relaxor is suggested to be governed by spin fluctuations due to inhomogeneity in the spiral magnetic ordering induced by the A-site Ca doping. It is shown that the 5% Ca doping appears to induce faster reduction of spin fluctuation with decreasing temperature. Our pSR data in applied longitudinal fields (LF) also indicate the possible occurrence of inhomogeneous internal field although a more detailed study is required for its clarification and verification.