EFFECTS OF HIGH PRESSURE, MAGNETIC FIELDS AND SUBSTITUTIONS ON MULTIFERROIC MAGNETOELECTRIC SYSTEMS

Rajit Chaudhury (University of Houston)

We have investigated various materials with regard to the effects of pressure, field, and ionic substitution on their multiferroic properties. In MnWO4 we find that replacement of Mn+2 by Fe+2 or Zn+2 ions results in the suppression (Fe) or enhancement (Zn) of the ferroelectric (FE) phase. Novel effects are observed in external magnetic fields (H), for example the field-induced re--entrant FE/spiral magnetic phase in Mn1-xFexWO4. The complete x-H-T phase diagrams are constructed for these compounds from polarization, dielectric constant, specific heat and magnetization data. The anisotropic Heisenberg model was solved to qualitatively understand the effects of substitution and field. The sensitivity of the FE polarization under high pressure was investigated. Pressure does suppress the FE polarization of Ni3V2O8 and MnWO4. In YMn2O5, however, external pressure did reverse the FE polarization at low temperature. We have conducted high resolution thermal expansion measurements revealing significant lattice anomalies and correlated these results with the observed pressure effects. The Magnetoelectric properties of single crystals of Ho1.xNdxFe3(BO3)4 (for x = 0.0, 0.25, 0.5, 0.75) was studied thoroughly. H . T phase diagram has completely been resolved for H.C axis and H.A axis from the thermodynamic, magnetic and polarization data. Magnetic, magnetostriction and magnetoelectric properties of d-electron free TmAl3(BO3)4 was investigated between room temperature and 2 K. The magnetoelectric polarization is proportional to the magnetostriction. We show that the rare-earth moment itself can generate a large magnetoelectric effect which makes it easier to study and to understand the origin of the magnetoelectric interaction in TmAl3(BO3)4.

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