Alexander N. Vasil'ev

Novel Phase Transition in Spin-1/2 Linear Chain Systems: NaTiSi2O6 and LiTiSi2O6

We synthesized a well-characterized powder sample of NaTiSi 2 O 6 , which had been missing as a spin-1/2 compound in one-dimensional (1D) magnets of the pyroxene family, and measured the magnetic s...

Structural and magnetic properties of Ni2MnGa

Abstract The martensitic phase transition from a cubic to a tetragonal structure on cooling in the shape-memory ferromagnetic Heusler alloy Ni2MnGa is investigated. The martensitic-transition temperature TM, known to be 205 K for the nominal composition, was expected to increase with increasing Ni content of the alloy. For the samples Ni2(1 + δ)Mn1 − δGa1 − δ with δ = 0, 0.046 and 0.10, respectively, the Curie temperature has been determined as 380 K independent of composition. TM for the sample with δ = 0.046 is also near 205 K, but the sample with δ = 0.10 is single phase and remains tetragonal up to the Curie temperature. The spontaneous polarization of this magnetically uniaxial phase has been determined to be JS = 0.16T and an estimate of the magnetocrystalline anisotropy constant is K1 ≈ 80kJm−3.

Raman, infrared and optical spectra of the spin-Peierls compound NaV2O5

We have measured polarized spectra of Raman scattering, infrared and optical transmission of NaV_2O_5 single crystals above the temperature of the spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines are strongly asymmetric, due to the spin-phonon interaction. In addition to the phonon lines, a broad band was observed in the c(aa)c Raman spectrum and in the E||a FIR transmission spectrum. A possible origin of these bands is discussed. The absorption band at 10000 cm-1 1.25 eV is attributed to vanadium d-d electronic transitions while the absorption edge above 3 eV is supposed to correspond to the onset of charge-transfer transitions.

ANOMALOUS THERMAL CONDUCTIVITY OF NAV2O5 AS COMPARED TO CONVENTIONAL SPIN-PEIERLS SYSTEM CUGEO3

Submitted to: Phys. Rev. Lett. Abstract: A huge increase of thermal conductivity k is observed at the phase transition in stoichiometric NaV2O5. This anomaly decreases and gradually disappears with deviation from stoichiometry in Na(1-x}V2O5 (x = 0.01, 0.02, 0.03, and 0.04). This behavior is compared with that of pure and Zn-doped CuGeO3 where only modest kinks in the k(T) curves are observed at the spin-Peierls transition. The change of k at critical temperature Tc could be partially attributed to the opening of an energy gap in the magnetic excitation spectrum excluding the scattering of thermal phonons on spin fluctuations. However, the reason for such a strong anomaly in the k(T) may lie not only in the different energy scales of CuGeO3 and NaV2O5, but also in the different character of the phase transition in NaV2O5 which can have largely a structural origin, e.g. connected with the charge ordering.

Magnetic properties of Cu2V2O7

Abstract Magnetic measurements were performed on Cu2V2O7. Above ∼70 K paramagnetic susceptibility obeys the Curie–Weiss law. Value of effective magnetic moment μeff=1.9μB corresponds to that of Cu2+. The Weiss temperature Θ=−66 K is negative and indicates an antiferromagnetic exchange interaction between Cu2+ ions. At T c =35 K a spontaneous magnetization arises due to the transition from paramagnetic state into either ferrimagnetic or canted antiferromagnetic state.

Thermal conductivity of inorganic spin–Peierls compounds

Abstract Huge increase of thermal conductivity κ is observed at the phase transition in stoichiometric NaV2O5. This anomaly decreases and gradually goes away with deviation from the stoichiometry in Na1−xV2O5 (x=0.01, 0.02, 0.03, and 0.04). These properties are compared with behaviour of pure and Zn-doped CuGeO3 where only modest kinks in κ(T) curves have been observed at spin–Peierls transition.

The magnetic ordering in the mixed valence compound beta-Na0.33V2O5

The low-temperature electron spin resonance (ESR) spectra and the static magnetization data obtained for the stoichiometric single crystals of

Magnetostriction of the spin-Peierls compound CuGeO3

\ensuremath{\beta}\ensuremath{-}{\mathrm{Na}}_{0.33}{\mathrm{V}}_{2}{\mathrm{O}}_{5}

Weak ferrimagnetism, compensation point, and magnetization reversal in Ni(HCOO)(2)center dot 2H(2)O

indicate that this quasi-one-dimensional mixed-valence compound demonstrates at

Magnetization reversal in weak ferrimagnets and canted antiferromagnets

{T}_{N}=22 \mathrm{K}