S. V. Verkhovskii

Influence of the doping level on the charge distribution among the inequivalent CuO2 layers in Tl2Ba2Ca2Cu3O10−δ : a NMR study

Abstract 63 Cu and 17 O NMR measurements in the normal and superconducting states of Tl2Ba2Ca2Cu3O10−δ with different δ are reported. In the overdoped Tl2223 sample with Tc=117 K (Tcopt=123 K) and δ1 17 K are revealed for inequivalent CuO2 layers. For the inner CuO2 layer with the square oxygen coordination of Cu the decrease of 17 K with temperature is more gradual. In going towards the underdoped Tl2223 with Tc=104 K and δ2>δopt the changes of 63,17 K with temperature are found to be the same for both types of copper layers. The quadrupole coupling constants for copper and oxygen from different CuO2 layers were obtained. From the variations with doping of the valence contribution to the electric field gradient at copper sites, we estimate both the hole numbers at Cu and oxygen sites and the real concentration of mobile hole carriers nh in each of inequivalent CuO2 layers. In the overdoped Tl2223 sample the charge density in the inner layer differs from the one in the outer plane (with five-fold oxygen coordination for Cu). Our results show that the inhomogeneity of the charge distribution disappears in the underdoped regime. The results are compared with calculations of the charge distribution among the CuO2 planes in multilayered cuprates reported by Haines and Tallon [E.M. Haines, J.L. Tallon, Phys. Rev. B 45 (1992) 3127].

Reduction in the electron density of states in superconducting MgB 2 disordered by neutron irradiation: 11 B and 25 Mg NMR estimates

NMR line shift and nuclear spin-lattice relaxation rate T_1^{-1} of 11B and 25Mg were measured in superconducting MgB_2 (T_c^{ons}=38K) structurally disordered by nuclear reactor neutrons up to the fluence of thermal neutrons

Electronic states of boron in superconducting MgB2 studied by11B NMR

\Phi=1 10^{19} cm^{-2}. The temperature of superconducting transition was shifted down to T_{c,irrad}^{ons}=7K under irradiation. The change due irradiation in the partial electron density of states (DOS) at the Fermi energy of boron and magnesium were traced by taking into account that T_1^{-1} of 11B and 25Mg are determined by hyperfine magnetic interactions with carriers. It was revealed that electronic states near E_F of Mg are influenced negligibly by irradiation whereas partial DOS of the B 2p_{x,y} states reduces greatly in irradiated MgB_2. The NMR estimates for DOS using the McMillan formula show that critical temperature decreases in irradiated MgB_2 mainly due to reduction in the partial DOS of p states of boron.

Interlayer CuO2 antiferromagnetic spin correlations in Tl-based superconducting Tl2Ba2CanCun+1O6+2n and Tl0.5Pb0.5Sr2Ca0.8Y0.2Cu2O7 oxides: 63Cu and 205Tl NMR and spin-lattice relaxation data

Nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rateT1−1 of11B have been measured in superconducting polycrystalline MgB2 with 7cons = 39.5 K. It is shown that (T1T−1 and the Knight shiftKs are independent of temperature and nearly isotropic aboveTc. Both of these quantities are decreased gradually in going to the superconducting state. According to NMR data the density of states near the Fermi level is flat at the scale of about 500 K. Some conclusions on the orbital content of the density of states at the Fermi level were drawn and compared with the results of the band structure calculations.

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

Abstract We analyzed 205 Tl and 63 Cu spin-lattice relaxation rate data T −1 1 for thallium-based Tl 0.5 Pb 0.5 Sr 2 Ca 0.80 Y 0.2 Cu 2 O 7 ( T ons c = 107 K) and Tl 2 Ba 2 Ca n Cu n +1 O 6+1 n ( T ons c = 104 K) ( n = 1), T ons c = 125 K ( n = 2)) cuprates which contain one or two TlO layers, respectively. The difference in temperature dependences T −1 1 ( 63 Cu) and T −1 1 ( 205 Tl) for the one TlO layer compound gives us evidence for the presence of interlayer antiferromagnetic spin correlations between the nearest copper atoms placed in the neighbouring CuO 2 layers.

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

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-lattice relaxation, NQR 63Cu and NMR 205Tl in Tl2Ba2CuO6+δ

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

Melting of the orbital order in LaMnO3probed by NMR

\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 .

Local distortions in the BiO6-octahedra sublattice of BaPbxBi1−xO3 as seen by 137Ba NMR/NQR

Abstract We measured the nuclear spin-lattice relaxation rate of 63 Cu and 205 Tl, the magnetic hyperfine shift of 205 Tl, and the NQR of 63 Cu in the raw of Tl 2 Ba 2 CuO 6+δ with different T c ( δ ) in the range 3–400 K, to investigate low-frequency spin dynamics in perovskite CuO 2 layers. The possibility is discussed of explaining the obtained results in terms of the “antiferromagnetic Fermi liquid” model proposed by Monien, Millis and Pines. We found that T c is lowered and growth of the uniform spin susceptibility χ ( q = 0) takes place which is accompanied by a decrease in the intensity of a short-wave AF spin correlation between copper atoms in the CuO 2 plane.

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

A. Trokiner, S. Verkhovskii, 2 A. Gerashenko, 2 Z. Volkova, O. Anikeenok, K. Mikhalev, M. Eremin, and L. Pinsard-Gaudart 5 LPEM, ESPCI ParisTech, UMR 8213, CNRS, 75005 Paris, France Institute of Metal Physics, Ural Branch of Russian Academy of Sciences, 620041 Ekaterinburg, Russia Institute of Physics, Kazan Federal University, 420008 Kazan, Russia Univ. Paris-Sud, Institut de Chimie Moléculaire et des Matériaux d’Orsay, UMR8182, Bat. 410, Orsay 91405 France CNRS, Orsay, 91405 France (Dated: January 18, 2014)