Dielectric and magnetic anomalies and spin frustration in hexagonal<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>R</mml:mi><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo>(</mml:mo><mml:mi>R</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">Y</mml:mi><mml:mo>,</mml:mo></mml:math>Yb, and Lu)

Abstract

Single crystals of hexagonal $R{\mathrm{MnO}}_{3}$ $(R=\mathrm{Y},$ Yb, and Lu), where Mn ions form the triangular lattice, were investigated, focusing on their dielectric/magnetic anomalies as well as geometrical spin frustration. It is found that the ratio of a Weiss temperature to ${T}_{\mathrm{N}}$ is $\ensuremath{\sim}10$ in $R{\mathrm{MnO}}_{3},$ indicating the dominant role of strong geometrical frustration. The effect of geometrical frustration also appears in specific heat, which shows a presence of a substantial amount of residual magnetic contribution below ${T}_{\mathrm{N}},$ indicating that a part of the spins are still fluctuating at $T\ensuremath{\ll}{T}_{\mathrm{N}}.$ It is also found that the dielectric anomaly at ${T}_{\mathrm{N}}$ is strongly anisotropic, suggesting a unique correlation between magnetism and dielectric properties in these compounds.