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Influence of the Pressure on the Multiferroicity of RMn2O5

Abstract : The series of multiferroic RMn2O5 has been extensively studied due to its strong magneto-electric coupling. The ferroelectricity origin has been clarified as the exchange striction mechanism. As the variations of the interatomic distances modified by the external pressure can greatly affect the multiferroic properties, it is essential to understand the microscopic origin of this effect. In this thesis, we have systematically studied the multiferroic properties of the RMn2O5 compounds by using powder X-rays diffraction and powder neutron diffraction (PND) under pressure. Through the measurements of the powder X-rays diffraction of the RMn2O5 (R = Pr, Nd, Sm, Gd, Tb, and Dy) under pressure at room temperature, the lattice parameters and atomic displacement we obtained are comparable to the calculation by the density functional theory. Thus, we have been able to figure out the general relation between the pressure and the exchange iterations J1, J4 and J6, which can give us some indication to understand the microscopic origin of the pressure effect at low temperature. Through the measurements of the PND of the RMn2O5 (R = Pr, Dy, Gd and Sm) under pressure at low temperature, we have determined the magnetic structure of the pressure induced commensurate magnetic (PCM) phase. The collinear spins of Mn ions, nil spin of Pr3+ with the indication of the ferroelectricity measurements at low pressure suggest the strong electric polarization of the PrMn2O5at high pressure. Based on a subtle energy balance among the exchange interaction J1, the R-Mn exchange interaction J6 and the anisotropy of the rare earth, we have proposed the microscopic origin of different kzof the commensurate magnetic phase. These results certainly pave the way to fully understand the origin of the pressure influence in the RMn2O5 family.
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Submitted on : Tuesday, October 16, 2018 - 8:00:08 PM
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Wei Peng. Influence of the Pressure on the Multiferroicity of RMn2O5. Strongly Correlated Electrons [cond-mat.str-el]. Université Paris-Saclay, 2018. English. ⟨NNT : 2018SACLS296⟩. ⟨tel-01897078v1⟩

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