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Investigation of thermal and magnetic properties of defects in a spin-gap compound NaV2O5

A. I. Smirnov·S. S. Sosin·R. Calemczuk·V. Villar·C. Paulsen·M. Isobe·Y. Ueda
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Abstract

The specific heat, magnetic susceptibility and ESR signals of a Na-deficient vanadate Na_xV_2O_5 (x=1.00 - 0.90) were studied in the temperature range 0.07 - 10 K, well below the transition point to a spin-gap state. The contribution of defects provided by sodium vacancies to the specific heat was observed. It has a low temperature part which does not tend to zero till at least 0.3 K and a high temperature power-like tail appears above 2 K. Such dependence may correspond to the existence of local modes and correlations between defects in V-O layers. The magnetic measurements and ESR data reveal S=1/2 degrees of freedom for the defects, with their effective number increasing in temperature and under magnetic field. The latter results in the nonsaturating magnetization at low temperature. No long-range magnetic ordering in the system of defects was found. A model for the defects based on electron jumps near vacancies is proposed to explain the observed effects. The concept of a frustrated two-dimensional correlated magnet induced by the defects is considered to be responsible for the absence of magnetic ordering.

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A. I. Smirnov, S. S. Sosin, R. Calemczuk, V. Villar, C. Paulsen, M. Isobe, Y. Ueda. 2000-03-24. Investigation of thermal and magnetic properties of defects in a spin-gap compound NaV2O5. https://doi.org/10.1103/physrevb.63.014412

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