Magnetic two-dimensional short-range order in hexagonal manganites

Abstract

Hexagonal manganites REMnO3 consist of layers of two-dimensional connected distorted MnO5 bipyramids separated by distorted layers of RE, leading to frustrated Mn3+–O2−–Mn3+ in-plane exchange paths (superexchange) and Mn3+–O2−–O2−–Mn3+ interplane exchange paths (super-superexchange). We report single-crystal diffraction experiments (RE=Ho,Er,Y) indicating magnetic 2D short-range order up to temperatures of T=150 K (TN∼74 K), and SQUID magnetization data (RE=Y) indicating short-range order up to at least 250 K. Fits of a model based on an extended mean-field theory to the single-crystal data show in-plane exchange about 3 orders of magnitude stronger than the interplane exchange, explaining the unusual strong deviation from the Curie–Weiss law of the SQUID magnetization data.

Spin dynamics ofYMnO3studied via inelastic neutron scattering and the anisotropic Hubbard model

“…YMnO 3 is a quasi-2D magnetic system. So one expects diffuse scattering rods parallel to c * close to T N Ϸ 70 K. We have, indeed, found such rod scattering above T N , in agreement with the results of Lonkai et al 21 We performed several Q scans perpendicular to the rod across Q = ͑1,0,0.11͒. Fig.…”

Hexagonal Manganites—(RMnO3): Class (I) Multiferroics with Strong Coupling of Magnetism and Ferroelectricity

“…The sharp slope change is consistent with earlier reports for single crystals [144][145][146]. However, the magnetic signature at may be less clear in powder samples, possibly due to sample quality or grain size problems [43,90,95,[147][148][149][150].…”

“…The discussion about the magnetic symmetry of YMnO 3 below the Néel temperature is even more complicated after signatures of diffuse scattering as well as unconventional short range spin fluctuations have been reported above as well as in the ordered phase [147,148,[155][156][157]. The results seem to be consistent with a quasi two-dimensional frustrated magnetic system with weak interplane coupling and a spin liquid phase above which extends into the magnetically ordered phase below .…”

Effect of substitution of Y on the structural, magnetic, and thermal properties of hexagonal DyMnO3single crystals

“…In the case of YMnO 3 , a clear deviation from the CW description was observed at 250 K itself, signifying the presence of spin fluctuations related to a two-dimensional (2D) short-range type. 21 Similarly, in the present frustrated magnet also, a CW description may not be the accurate one. The observed linearity of inverse susceptibility still has a major contribution from the paramagnetic susceptibility of Dy.…”

“…From the specific heat measurements it is found that the Y dilution enhances O4 are oxygens in the basal plane of the MnO 5 bipyramid). 21 Insertion of nonmagnetic Y atoms between the layers of Mn bipyramids will only weaken the interlayer exchange further. The fact that the T Mn N has increased indicates the importance of the intralayer coupling between Mn in the basal plane.…”