V. V. Ogloblichev

Magnetic structure of low-dimensional LiCu2O2 multiferroic according to 63,65Cu and 7Li NMR studies

The complex NMR study of the magnetic structure of LiCu2O2 multiferroic has been performed. It has been shown that the spin spirals in LiCu2O2 are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu2+ chains. A magnetic field of H0 = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H0 ‖ b.

Spin susceptibility of Ga-stabilized δ-Pu probed by 69Ga NMR

Spin susceptibility of stabilized \delta phase in the Pu-Ga alloy is studied by measuring {69,71}^Ga NMR spectra and nuclear spin-lattice relaxation rate {69}T_{1}^{-1} in the temperature range 5 - 350 K. The shift ({69}^K) of the {69,71}^Ga NMR line and {69}^T_{1}^{-1} are controlled correspondingly by the static and the fluctuating in time parts of local magnetic field arisen at nonmagnetic gallium due to transferred hyperfine coupling with the nearest f electron environment of the more magnetic Pu. The nonmonotonic with a maximum around 150 K behavior of {69}^K(T) \chi_{s,5f}(T) is attributed to the peculiarities in temperature dependence of the f electron spin susceptibility \chi_{s,5f}(T) in \delta phase of plutonium. The temperature reversibility being observed in {69}^K(T) data provides strong evidence for an electronic instability developed with T in f electron bands near the Fermi energy and accompanied with a pseudogap-like decrease of \chi_{s,5f}(T) at T<150 K. The NMR data at high temperature are in favor of the mainly localized character of 5f electrons in \delta phase of the alloy with characteristic spin-fluctuation energy \Gamma(T) T^{0.35(5)}, which is close to

Features of the magnetic state of ƒ electrons in the stabilized δ phase of the Pu0.95Ga0.05 alloy

\Gamma(T) T^{0.5} predicted by Cox et al. [J. Appl. Phys. 57, 3166 (1985)] for 3D Kondo-system above T_Kondo}. The dynamic spin correlations of 5f electrons become essential to consider for {69}^T_{1}^{-1}(T) only at T<100 K. However, no NMR evidences favoring formation of the static magnetic order in \delta-Pu were revealed down to 5K .

Magnetic structure of the low-dimensional magnet NaCu2O2: 63,65Cu and 23Na NMR studies

For the Pu0.95Ga0.05 alloy belonging to the stabilized δ phase of the Pu-Ga system, the 69Ga NMR spectra are measured in the temperature interval 10–650 K and the static magnetic susceptibility χ is measured in the interval T = 20–350 K. In the region T > T* = 235 K, the temperature-dependent magnetic part of the shift K(T) of the Ga NMR line reproduces the χ(T) dependence and follows the Curie-Weiss law K(T) ∼ (T + Θ)−1 with Θ = 280(40) K, which is typical of incoherent spin fluctuations of localized ƒ electrons in concentrated nonmagnetic Kondo systems. The estimate of the effective magnetic moment μeff, 5ƒ(ge = 2) = 0.15(5)μB per Pu atom testifies to a strong suppression of the spin magnetism in the alloy, where the configuration of the ƒ shell of a Pu ion is close to atomic-like ƒ6. The difference between the K(T) and χ(T) dependences observed for the alloy in the temperature range T < T* is analyzed in terms of the two-fluid description of Kondo lattices developed by Pines et al. [15, 16] in application to the coherent state of a heavy-fermion liquid. Possible causes for the anomalous increase in long-wave contributions in the spatial dispersion of the localized spin susceptibility component of ƒ electrons χƒƒ at temperatures below 50 K are discussed.

Helical magnetic structure in a quasi-one-dimensional LiCu2O2 multiferroic crystal according to 63,65Cu NMR studies

The magnetic structure of a quasi-one-dimensional frustrated NaCu2O2 magnet single crystal is studied by NMR. The spatial orientation of the planar spin spirals in the copper-oxygen Cu2+-O chains is determined, and its evolution as a function of the applied magnetic field direction is analyzed.

NMR study of the paramagnetic state of low-dimensional magnets LiCu2O2 and NaCu2O2

The NMR spectra of 63Cu and 65Cu natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (Tc = 23 K) in zero magnetic field and in applied magnetic field H0 = 94 kOe parallel to the c axis of the crystal. In LiCu2O2 below Tc, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H0 = 0 with the ab plane. The high magnetic field (H0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.

51V-NMR study of the Kagome staircase compound Co3V2O8

A comprehensive NMR study of the magnetic properties of single crystal LiCu2O2 (LCO) and NaCu2O2 (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for 63,65Cu, 7Li, and 23Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.

Charge-ordered state in half-doped Bi-based manganites studied by 17O and 209Bi NMR

Kagome staircase compound Co3V2O8 (S = 3/2) has a structure very similar to multiferroic compound Ni3V2Og (S = 1), but their magnetic phase diagrams differ noticeably. We present the results of the first NMR study in Co3V2O8 single crystal. From 51V-NMR spectra, the components of electric field gradient (EFG) tensor and of magnetic shifts tensor, Ki, are obtained. The temperature dependences of NMR shifts 51Ki for each main crystal axis direction are well described by a spin contributions in the paramagnetic phase. In ferromagnetic phase the zero field 51V-NMR spectrum is observed in the temperature range of 1.5–6.3 K.

Charge Distribution and Hyperfine Interactions in the CuFeO 2 Multiferroic According to 63,65 Cu NMR Data

We present a

NMR study of the electric field gradient in the paramagnetic phase of M3V2O8 (M = Co, Ni) compounds

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