RESUMO
We report the bulk magnetic characterization of a dimeric chain material, BiMnVO5, by means of magnetic susceptibility, magnetization and heat capacity measurements. Our results provide compelling evidence of an antiferromagnetic (AFM) transition at (T N) ~ 11.5 K. Moreover, the magnetic entropy change in zero field saturates to 14.6 J mol-1 K-1 which is close to the total spin entropy of Mn2+. The development of long-range magnetic order in this chain material demonstrates the interplay of strong intra-chain and inter-chain interactions between the dimers, in addition to the intra-dimer interaction. Low-temperature (T < T N) heat capacity data indicate the presence of a gap (Δ/k B ≈ 5 K) in the spin excitations. Furthermore, the isothermal magnetization below T N shows an anomaly in the slope between 30 and 40 kOe which is suggestive of a spin-flop transition. Such a low-field spin-flop transition and gapped spin wave excitations may be attributed to the presence of (weak) magnetic anisotropy in this material. We attempt to construct a phase diagram in the magnetic field-temperature plane by extracting data from in-field heat capacity and isothermal magnetization measurements.
RESUMO
We report that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Néel temperature (TN) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10 K), mimicking the 'reentrant' multiglass phenomenon. Such a behavior is not known among undoped compounds. A new finding in the field of multiferroics is that the characteristic magnetic feature at low temperatures moves towards higher temperatures in the presence of a magnetic field (H), whereas the corresponding dielectric feature shifts towards lower temperatures with H, unlike the situation near TN. This observation indicates that the alignment of spins by external magnetic fields tends to inhibit glassy-like slow electric-dipole dynamics, at least in this system, possibly arising from peculiarities in the magnetic structure.
