Understanding the multiferroicity in TmMn(2)O(5) by a magnetically induced ferrielectric model

The magnetically induced electric polarization behaviors in multiferroic TmMn(2)O(5) in response to varying temperature and magnetic field are carefully investigated by means of a series of characterizations including the high precision pyroelectric current technique. Here polycrystalline rather than single crystal samples are used for avoiding the strong electrically self-polarized effect in single crystals, and various parallel experiments on excluding the thermally excited current contributions are performed. The temperature-dependent electric polarization flop as a major character is identified for different measuring paths. The magneto-current measurements indicate that the electric polarization in the low temperature magnetic phase region has different origin from that in the high temperature magnetic phase. It is suggested that the electric polarization does have multiple components which align along different orientations, including the Mn(3+)-Mn(4+)-Mn(3+) exchange striction induced polarization P(MM), the Tm(3+)-Mn(4+)-Tm(3+) exchange striction induced polarization P(TM), and the low temperature polarization P(LT) probably associated with the Tm(3+) commensurate phase. The observed electric polarization flop can be reasonably explained by the ferrielectric model proposed earlier for DyMn(2)O(5), where P(MM) and P(TM) are the two antiparallel components both along the b-axis and P(LT) may align along the a-axis. Finally, several issues on the unusual temperature dependence of ferroelectric polarizations are discussed.