Study of magnetic inhomogeneity in β-Cu3Fe4V6O24

Abstract

The temperature dependence of dc magnetization and electron paramagnetic resonance (EPR) spectra of the β-Cu3Fe4V6O24 multicomponent vanadate were investigated. Dc magnetic measurements showed the presence of strong antiferromagnetic interactions (Curie-Weiss temperature, Θ ∼ 80 K) at high temperatures, while zero-field-cooled (ZFC) magnetization revealed a cusp-like maximum in low fields at T f1 = 4.4 K, which coincides with the splitting of the ZFC and FC curves. Another maximum was registered at T f2 = 3.0 K. These two temperatures (T f1 and T f2) could be regarded as freezing temperatures in the spin glass state of two magnetic sublattices of Fe1 and Fe2 ions. The EPR spectrum of β-Cu3Fe4V6O24 is dominated by a nearly symmetrical, very intense and broad resonance line centered at g eff ∼ 2.0 that could be attributed to iron ions. Below 10 K, an additional EPR spectrum with g 1 = 2.018(1) and g 2 = 2.175(1) appears, as well as a very weak line at geff = 1.99(1). The former spectrum is probably is due to divalent copper ions, and the latter line due to vanadium V4+ complexes. The temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) was determined in the range of 3–300 K. Two low-temperature maxima in the temperature dependence of the integrated intensity (at 40 and 6 K) were fitted with a function suitable for pairs of exchange-coupled Fe3+ ions. A comparison of dc magnetic susceptibility and EPR integrated intensity indicates the presence of spin clusters, which play an important role in determining the low-temperature magnetic response of β-Cu3Fe4V6O24.