Successive phase transitions to antiferromagnetic and weak-ferromagnetic long-range order in the quasi-one-dimensional antiferromagnetCu3Mo2O9

Abstract

Investigation of the magnetism of ${\mathrm{Cu}}_{3}{\mathrm{Mo}}_{2}{\mathrm{O}}_{9}$ single crystal, which has antiferromagnetic (AF) linear chains interacting with AF dimers, reveals an AF second-order phase transition at ${T}_{N}=7.9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Although weak-ferromagnetic-like behavior appears at lower temperatures in low magnetic fields, complete remanent magnetization cannot be detected down to $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. However, a jump is observed in the magnetization below weak-ferromagnetic (WF) phase transition at ${T}_{c}\ensuremath{\simeq}2.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ when a tiny magnetic field along the $a$ axis is reversed, suggesting that the coercive force is very weak. A component of magnetic moment parallel to the chain forms AF long-range order (LRO) below ${T}_{N}$, while a perpendicular component is disordered above ${T}_{c}$ at zero magnetic field and forms WF-LRO below ${T}_{c}$. Moreover, the WF-LRO is also realized by applying magnetic fields even between ${T}_{c}$ and ${T}_{N}$. These results are explainable by both magnetic frustration among symmetric exchange interactions and competition between symmetric and asymmetric Dzyaloshinskii\char21{}Moriya exchange interactions.