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

Abstract

Investigation of the magnetism of Cu 3 Mo 2 O 9 single crystal, which has antiferromagnetic ͑AF͒ linear chains interacting with AF dimers, reveals an AF second-order phase transition at T N = 7.9 K. Although weakferromagnetic-like behavior appears at lower temperatures in low magnetic fields, complete remanent magnetization cannot be detected down to 0.5 K. However, a jump is observed in the magnetization below weakferromagnetic ͑WF͒ phase transition at T c Ӎ 2.5 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 ͑LRO͒ 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-Moriya exchange interactions.

NMR study on field-induced charge anomaly in Cu3Mo2O9

“…An appreciable hysteresis is observed within the jump region, indicating that this phase transition is of 1 st order. The amount of the magnetization jump at H SF is roughly a half of that at 1 T [3]. As shown in Fig.…”

“…There are two chains called  and  connected with the glide symmetry in a unit cell [3]. The two antiferromagnetic interactions J 3 in the chain and J 4 in the dimer are dominant, while the chain-dimer interactions J 1 and J 2 are very weak [3][4][5]. However the effect of J 1 and J 2 cannot be neglected, because they are responsible for the coupling between the chain and the dimer-like sites.…”

“…There are three copper sites; Cu1 resides on the linear chain that runs along b-axis, and the other two sites Cu2 and Cu3 locating at slightly inequivalent positions, form a dimer-like pair clinging around the chains. There are two chains called  and  connected with the glide symmetry in a unit cell [3]. The two antiferromagnetic interactions J 3 in the chain and J 4 in the dimer are dominant, while the chain-dimer interactions J 1 and J 2 are very weak [3][4][5].…”

“…The target material of this report is a quasi one dimensional antiferromagnetic quantum spin system Cu 3 Mo 2 O 9 , consisting of a spin-1/2 linear chain and spin-1/2 dimer-like pair coupling weakly with one another [3][4][5]. Existence of these two spin degrees of freedom and of the weak frustration effect suggested an unprecedented spin state, on which intensive studies have been made so far.…”

“…The intensive study on magnetization and specific heat by Hamasaki et al [3] has revealed that a long range magnetic order occurs at T N =7.9 K, and that the ordered state is accompanied by a weak ferromagnetism due to Dzyaloshinsky-Moriya interaction. Just below T N , weak ferromagnetic moments are randomly oriented at zero field, and aligned under a very weak field below 1 T, showing a metamagnetism.…”