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Magnetic anisotropy of the tetramer spin S = 1/2 system SeCuO3

Low-dimensional magnetic systems present very interesting and fertile area for investigating magnetism in materials. Due to relatively simple magnetic lattices these compounds are ideal for theoretical studies. At the same time, low-dimensional magnetic systems are also realized in real materials allowing us parallel experimental research of these materials. Combined results of theory and experiment brings about understanding of magnetic interactions in materials. A large number of different ground states can be realized in low-dimensional spin systems, depending on the dimensionality of magnetic lattice, symmetry of crystal lattice, presence of frustration, defects etc. Among the novel low-dimensional spin systems is SeCuO3 where dominant magnetic interactions between spins S=1/2 create a lattice of isolated tetramers [1]. Due to weak interaction between tetramers this systems exhibits long-range antiferromagnetic order below $T_N=8$~K. It was observed that temperature dependence of magnetic susceptibility cannot be satisfactorily explained by the isolated tetramer model [1]. In magnets with copper spin S = 1/2 with interactions described by Heisenberg Hamiltonian the main source of magnetic anisotropy is the electron g – factor anisotropy, and much smaller contribution can come from anisotropic exchange interaction. We present detailed experimental study of magnetic anisotropy using torque magnetometry and electron spin resonance (ESR). We observe a rotation of magnetic axes with temperature in the $ac$ crystallographic plane which correlates with the rotation of the $g$ tensor only at temperatures $T>50$~K. Although the $g$ tensor changes with temperature, the average $g$ value is temperature-independent. Thus, the temperature dependence of the $g$ factor is not the only reason for disagreement of theory and experiment. Temperature dependence of susceptibility anisotropy and the rotation of magnetic axes observed in torque are most prominent below T=50~K where the g tensor is temperature-independent. This suggests that other contributions to magnetic anisotropy, such as Dzyaloshinskii-Moriya interaction which is allowed by symmetry, have significant influence on the magnetism of this quasi-0D spin system. [1] I. Živković. D. M. Djokić, M. Herak, D. Pajić, K. Prša, P. Pattison, D. Dominko, Z. Micković, D. Cinčić

Magnetic anisotropy; low-dimensional spin systems

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