Low-dimensional magnetism of spin-½ chain systems of α- and β-TeVO4: A comparative study

Abstract

We present a comparative study of the low-dimensional compounds α-and β-TeVO 4 . Our data clearly show that the change in the local coordination geometry of V 4+ ions comparing α-and β-TeVO 4 leads to a drastic differences in the magnetic properties. Despite sharing the same crystal structure, the two compounds realize different magnetic exchange topologies. Both compounds exhibit a transition from ferro-to antiferromagnetic correlations with decreasing temperature. This effect however is driven by different mechanisms for both compounds. Additionally, a dimensional crossover is found in β-TeVO 4 . PACS

Magnetic anisotropy in the frustrated spin-chain compoundβ−TeVO4

“…A Curie-Weiss fit of the data in the 100 − 380 K range ( Fig. 2A, inset) gives a Curie constant C = 0.374 emu K mol −1 and θ CW = −2.1 K indicating a nearly perfect balance of FM and AFM couplings, in agreement with earlier work [18]. The low-temperature anomalies are more clearly visible when the low temperature range is expanded ( Fig.…”

“…At lower temperatures, the NMR lines broaden, although no abrupt changes are observed around 150 K, where Gnezdilov et al [18] expected a structural phase transition. The Knight shift (K) follows bulk magnetic susceptibility (χ), as shown in Fig.…”

“…Subsequently, magnetic susceptibility of β-TeVO 4 was re-analyzed in the framework of the J 1 − J 2 model [17]. Gnezdilov et al [18] reported non-monotonic evolution of phonon frequencies and speculated on possible structural changes around 150 K and even on a change in the orbital state of V 4+ at low temperatures. Finally, Pregelj et al [19] performed detailed neutron-scattering experiments in zero field and observed a helical magnetic structure with the propagation vector k = (−0.208, 0, 0.423) below T N3 .…”

Density functional approach for the magnetism ofβ-TeVO4

“…From an experimental point of view, the first in-depth reports of the magnetic properties of β-TeVO 4 have been published only very recently [13,14] and emphasize the complex behavior of this compound. The temperature dependence of the magnetic susceptibility, showing a broad maximum at about 14 K, has been investigated carefully by Savina et al [13] and eventually interpreted as that of a uniform antiferromagnetic spin-1 2 chain with a single exchange coupling.…”

“…The occurrence of a broad crossover (T cros ≈ 130 K) separating two magnetic regimes dominated either by ferromagnetic correlations at high temperature or by antiferromagnetic correlations at low temperature has been proposed [13]. This crossover has recently been interpreted as a consequence of a V 4+ orbital reordering associated with a shift of the transition-metal ion away from the apical oxygen inside its coordination square pyramid [14]. Finally, a series of low-temperature magnetic phase transitions has been observed and attributed to the occurrence of a first long-range-ordered antiferromagnetic state (T N ≈ 4.65 K) followed by subsequent spin rearrangements [13].…”