Influence of doping on the spin dynamics and magnetoelectric effect in hexagonalY0.7Lu0.3MnO3

Abstract

We use inelastic neutron scattering to study spin waves and their correlation with the magnetoelectric effect in Y0.7Lu0.3MnO3. In the undoped YMnO3 and LuMnO3, the Mn trimerization distortion has been suggested to play a key role in determining the magnetic structure and the magnetoelectric effect. In Y0.7Lu0.3MnO3, we find a much smaller in-plane (hexagonal ab-plane) single ion anisotropy gap that coincides with a weaker in-plane dielectric anomaly at TN . Since both the smaller in-plane anisotropy gap and the weaker in-plane dielectric anomaly are coupled to a weaker Mn trimerization distortion in Y0.7Lu0.3MnO3 comparing to YMnO3 and LuMnO3, we conclude that the Mn trimerization is responsible for the magnetoelectric effect and multiferroic phenomenon in Y1−yLuyMnO3.PACS numbers: 75.30. Ds, 75.40.Gb, 75.50.Ee, 75.85.+t Driven by modern technology towards device miniaturization, there is considerable interest in multiferroic materials which exhibit both magnetic order and electrical polarization 1-7 . The hexagonal manganite RMnO 3 8,9 (where R is a rare-earth element with relatively small ionic radius) is a prototypical example of the so-called type-I multiferroics 10 with ferroelectric order at T c ∼900 K 11 and an antiferromagnetic (AFM) order at much lower temperature, T N ∼100 K 12 . A large dielectric anomaly occurs at T N 13-15 indicating strong magnetoelectric (ME) coupling in these materials. There has been a large amount of experimental work in recent years, with the aim to understand the microscopic mechanism for the coupling between magnetic and electric degrees of freedom in these materials. Although it is generally believed that the spin-lattice coupling plays an important role in determining the complex properties in RMnO 3 , much is unclear concerning the factors that influences the magnitude of the ME coupling 16,17 . In this Letter, we use inelastic neutron scattering (INS) and dielectric constant measurements to show that the magnitude of the ME coupling in multiferroic Y 0.7 Lu 0.3 MnO 3 is directly coupled to the strength of the Mn trimerization distortion in these materials in the AFM phase. Our results thus provide direct evidence that the Mn trimerization is responsible for the ME effect and multiferroic phenomenon in Y 1−y Lu y MnO 3 .The undoped compounds YMnO 3 and LuMnO 3 are characteristic hexagonal manganites where the Mn 3+ ions (Mn x position at x∼1/3) form a nearly ideal triangular lattice in the ab-plane above T N . YMnO 3 and LuMnO 3 undergo AFM transitions (to two different magnetic structures) at T N ∼75 K and T N ∼88 K respectively, accompanied by an isostructural transition with large atomic displacement for all atoms in the unit cell. In particular, a distinct change of the Mn atomic po- sition, namely the Mn trimerization distortion, occurs in the basal plane at T N 17 . As illustrated in Fig. 1, the Mn trimers distort in opposite directions in YMnO 3 and LuMnO 3 , expanding for YMnO 3 and contracting for LuMnO 3 . A recent theoretical study finds that the different ...

Doping effects on trimerization and magnetoelectric coupling of single crystal multiferroic (Y,Lu)MnO3

“…However, we should note that our observation seems to sit at variance with one recent dielectric constant measurement, which reported a much weaker change in the dielectric constant for their Y 0.7 Lu 0.3 MnO 3 sample [31].…”

HexagonalRMnO3: a model system for two-dimensional triangular lattice antiferromagnets

“…The dominant magnetic interaction that determines the 120 spin structure is the nearest neighbor superexchange interaction in the triangular Mn-O layer. Several inelastic neutron scattering experiments have so far reported the magnon dispersion relations for various h-RMnO 3 compounds (Sato et al, 2003;Vajk et al, 2005;Chatterji et al, 2007;Lewtas et al, 2010;Fabrè ges et al, 2009;Oh et al, 2013;Tian et al, 2014;Chaix et al, 2014). A simple spin Hamiltonian including only Heisenberg interactions in the Mn-O layer is given by…”

Recent progress on HYSPEC, and its polarization analysis capabilities

“…Two of these experiments have already resulted in publications [5,6], and many more are in preparation. Prospective users who are unsure which DGS at the SNS is best suited for their experiments are referred to a recent comparison paper [7].…”