Arsen Gukasov

Evidence for Magnetic-Field-Induced Quadrupolar Ordering in the Heavy-Fermion Superconductor PrOs4Sb12

Neutron diffraction experiments on the heavy-fermion superconductor PrOs 4 Sb 12 revealed that a small antiferromagnetic moment, parallel to [010] ( y -direction), is induced in the field-induced phase ( H ∥ z ). The analysis, based on the Γ 1 singlet ground state crystal field model, shows that antiferro-order of O y z -type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs 4 Sb 12 is the Γ 1 singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

Charge order and one-dimensional properties of Yb4As3

Abstract A polarized neutron diffraction experiment gives direct evidence for a charge order in the extremely low-carrier system Yb4As3. Inelastic neutron scattering experiments on Yb4As3 revealed the existence of low-energy spin excitations that are characteristic of a one-dimensional antiferromagnetic coupling at low temperatures. The results indicate that the one-dimensional arrangement of Yb3+ ions caused by the charge order plays a main role for the heavy-electron behavior in Yb4As3.

Determination of atomic site susceptibility tensors from polarized neutron diffraction data

Polarized neutron diffraction provides information about the magnetization density of each individual crystallographic site. In the present paper the role of the atomic site susceptibility tensor χij accounting for the magnetic response of individual atoms to an external magnetic field is discussed. The symmetry of this tensor is very similar to that of the tensor uij describing the thermal motion of atoms. By analogy with the atomic displacement parameters (ADPs), atomic susceptibility parameters (ASPs) can be introduced. The six independent ASPs can be determined from polarized neutron flipping ratio measurements and visualized as magnetic ellipsoids which are analogous to the thermal ellipsoids obtained from ADPs. If the local anisotropy is small, these magnetic ellipsoids approximate to spheres with diameters proportional to the induced magnetization. In other cases, anomalous (elongated or flattened) ellipsoids will occur. The ASPs have been determined for the compound Nd3−xS4 which has the Th3P4 structure. They correspond to strongly oblate magnetic ellipsoids; in contrast, in the isomorphous compound Sm3Te4 the magnetic ellipsoids are found to be prolate.

Polarized Neutron Diffraction as a Tool for Mapping Molecular Magnetic Anisotropy: Local Susceptibility Tensors in CoII Complexes

Polarized neutron diffraction (PND) experiments were carried out at low temperature to characterize with high precision the local magnetic anisotropy in two paramagnetic high-spin cobalt(II) complexes, namely [Co(II) (dmf)6 ](BPh4 )2 (1) and [Co(II) 2 (sym-hmp)2 ](BPh4 )2 (2), in which dmf=N,N-dimethylformamide; sym-hmp=2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methylphenolate, and BPh4 (-) =tetraphenylborate. This allowed a unique and direct determination of the local magnetic susceptibility tensor on each individual Co(II) site. In compound 1, this approach reveals the correlation between the single-ion easy magnetization direction and a trigonal elongation axis of the Co(II) coordination octahedron. In exchange-coupled dimer 2, the determination of the individual Co(II) magnetic susceptibility tensors provides a clear outlook of how the local magnetic properties on both Co(II) sites deviate from the single-ion behavior because of antiferromagnetic exchange coupling.

Anomalous spin-density distribution on oxygen and Ru in Ca(1.5)Sr(0.5)RuO(4): polarized neutron diffraction study.

By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in Ca(1.5)Sr(0.5)RuO(4). Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding micro(Ru)=0.346(11)micro(B), micro(O1)=0.076(6)micro(B), and micro(O2)=0.009(6)micro(B). The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the xy (t(2g) band) d orbitals.

Study of the structural phase transition in Gd2−xCexCuO4

Abstract The structural phase transition in Gd 2− x Ce x CuO 4 ( x = 0, 0.12) characterized by the rotation of the CuO 4 -squares around the c axis has been studied by different diffraction techniques. The order parameter of this transition is found to increase continuously below 658(1) K for Gd 2 CuO 4 and below 707.2(7) K for Gd 1.88 Ce .12 CuO 4 with an unusual temperature dependence. The rotation of the CuO 4 -squares is coupled to a spontaneous strain along the c -axis. Structure analysis of the undistorted high temperature T′-phase in Gd 2 CuO 4 indicates persisting local distortions.

Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi

We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions.

Field-Induced Spin-Ice-Like Orders in Spin Liquid Tb2Ti2O7

We have studied the field-induced magnetic structures in Tb2Ti2O7, in a wide temperature (0.3 < T < 270 K) and field (0 < H < 7 T) range, by single crystal polarized and unpolarized neutron diffraction, with H parallel[110] axis. A ferromagneticlike structure with k = 0 propagation vector is induced, whose local order at low field and low temperature is akin to spin ice. The four Tb ions separate in alpha and beta chains having different values of the magnetic moments, which is quantitatively explained by taking the crystal field anisotropy into account. Above 2 T and below 2 K, an antiferromagneticlike structure with k = (0,0,1) is induced besides the k = 0 structure. It shows a reentrant behavior and extends over a finite length scale. It occurs together with a broadening of the nuclear peaks, which suggests a field-induced distortion and magnetostriction effect.

Magnetization density in

A neutron scattering study of the magnetization density distribution in is reported. Results are compared with the Mossbauer data obtained for the same sample. Polarized neutron scattering measurements show that the magnetization aligned parallel to an applied field of 2 T is mostly due to the Fe atoms. The values of the magnetic moment at the three crystallographic sites occupied by the transition metal atom are (8f ), (8i) and (8j). A small magnetic moment is measured at the U site, aligned ferromagnetically with the Fe moments. So small a value appears to be due to a partial cancellation of the individual orbital and spin magnetic moment contributions of the actinide atom. The values of the hyperfine magnetic field at the three crystallographic sites occupied by the Fe atoms change in the same order as the magnetic moments determined by neutron scattering, although the ratio is not constant.

Neutron diffraction study of magnetic structure of and

Experiments using polarized and unpolarized neutrons have been performed on single crystals of and . A magnetic structure with a [001], easy axis and two types of uranium site having different values of the moment was found for both compounds. The values of magnetic moment at these two sites are 2.11 and for bismuthide, and 2.14 and for antimonide. The appearance of such a structure is ascribed to a low local symmetry of the U-ion environment and hybridization-mediated two-ion interactions.