Unique spin dynamics and unconventional superconductivity in the layered heavy fermion compound CeIrIn5: NQR evidence

We report measurements of the 115In nuclear spin-lattice relaxation rate ( 1/T1) between T = 0.09 and 100 K in the new heavy fermion (HF) compound CeIrIn5. At 0.4 < or = T< or = 100 K, 1/T1 is strongly T-dependent, which indicates that CeIrIn5 is much more itinerant than known Ce-based HFs. We find that 1/T1T, subtracting that for LaIrIn5, follows a (1 / T+straight theta)3/4 variation with straight theta = 8 K. We argue that this novel feature points to anisotropic, due to a layered crystal structure, spin fluctuations near a magnetic ordering. The bulk superconductivity sets in at 0.40 K below which the coherence peak is absent and 1/T1 follows a T3 variation, which suggests unconventional superconductivity with line-node gap.     

Specific heat below 1k some examples in magnetism

The measurement of specific heat below 1 K by means of a quasi-adiabatic calorimeter, employing adiabatic demagnetization for cooling, is described. The lattice, hyperfine and electronic contributions in the temperature domain 0.05 < T < 4 K are discussed briefly as an introduction to the analysis and exploitation of the magnetic contribution to the specific heat in magnetic insulators. The comparison with simple magnetic models is illustrated by the analysis of the specific heat data of the NdMO₃ perovskites, with M = nonmagnetic atom. The action of a magnetic field, albeit an internal field, is discussed using NdMO₃, M = Fe, Cr and Ni perovskite as examples. Finally, two molecular magnetic materials are discussed; Gd₂(ox)[Cu(pba)]₃[Cu(H₂O)₅]· 20H₂O as a candidate for ferromagnetic order in a rare earth transition metal complex, and Gd(hfac)₃NITR, with the nitronyl nitroxide magnetic radical interacting with the rare earth.     

Route to and from the NMR chaos in diamagnets

The route to and from the chaos via period doubling bifurcations in nuclear spin system with dipole-dipole interactions is investigated. The transition points are found. It is shown that route from the chaos proceeds according the Feigenbaum scenario. Received 19 August 1998 and Received in final form 15 December 1998     

High pressure NQR study of some monohydrogen arsenates with positive temperature coefficients

Existing studies of the NQR frequency of ⁷⁵ As nuclei in mono- and dihydrogen arsenates under high hydrostatic pressure have provided highly relevant information concerning the lattice dynamics of these compounds. Recent measurements in such crystals prove that totally different molecular mechanisms are responsible fo the temperature and pressure dependence of the NQR frequency in arsenates with positive and negative ?v/?T.     

Magnetic forces in thallium- and bismuth-based superconductors

Hysteretic force-separation relations for Tl, Bi and Y based superconductors and a magnet are compared. The magnitudes of the forces, the hysteresis, and the magnetic stiffness were all largest in the three-layer Tl₂Ba₂Ca₂Cu₃O_x compound, indicating strong flux pinning. The hysteresis in both two and three layer thallium compounds was sufficient to generate attractive forces as the superconductor and magnet were moved apart. The use of remanent fields to improve stability of levitated and suspended magnets is described.     

High temperature multiple transitions in bismuth-based superconductors

We report observation of possible superconducting transitions at 133 K, 117K and 105 K in Bi-Sr-Ca-Cu-O bulk samples which attain zero resistance state above the liquid nitrogen temperature (T_c(0)) = 80K). The transition at 105 K is prominent and shows a significant drop in the sample resistance. X-ray data depict characteristic superconducting peak at 20 = 5–6°. All the specimens show Meissner effect when cooled in liquid nitrogen.     

Detection of NQR in explosives

Kaliningrad State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 62–65, July, 1992.     

Z-scan study of third-order optical nonlinearities in bismuth-based glasses

The third-order optical nonlinearity was measured in bismuth-based glasses by Z-scan technique using femto-second laser pulses. Re(χ⁽³⁾) = 4.9 × 10⁻¹¹ esu at 748 nm was obtained in the glass containing 65.5 mol% of Bi₂O₃. Although, the wavelength dependence of Re(χ⁽³⁾) shows resonant effect significantly, relatively small nonlinear absorption coefficient β = 0.8 cm/GW at 769 nm was estimated. Bismuth-based glass exhibits the largest third-order optical nonlinearity in oxide glasses, indicating they are promising materials used for nonlinear optical devices.     

Performance of frequency-modulated pulses in NQR

This paper presents an analysis of the performance of frequency-modulated pulses and of pulses modulated simultaneously in amplitude and frequency in the pure nuclear quadrupolar resonance (NQR) spectroscopy of spin 3/2 nuclei. Computer simulations are given of the offset compensation efficiency of such pulses as applied to single crystals. Spin evolution equations were solved numerically. Experimental measurements, using FM pulses, of the³⁵Cl NQR of sodium chlorate (NaClO₃) single crystal and of mercuric chloride (HgCl₂) powder are reported. The results suggest that frequency modulated pulses are alternative pulses to composite pulses in NQR.     

Two-frequency composite pulses in NQR

The application of multiple-pulse sequences consisting of two-transition composite pulses for remote nuclear quadrupole resonance detection of explosives and narcotics is discussed. The pulse sequence for obtaining these pulses is described and it is shown that these pulses are equivalent to the pulse applied at the third (nonirradiated) transition. The loss of the signal intensity in this case is absent.     

Computational quantum magnetism: Role of noncollinear magnetism

We are witnessing today a golden age of innovation with novel magnetic materials and with discoveries important for both basic science and device applications. Computation and simulation have played a key role in the dramatic advances of the past and those we are witnessing today. A goal-driving computational science—simulations of every-increasing complexity of more and more realistic models has been brought into greater focus with greater computing power to run sophisticated and powerful software codes like our highly precise full-potential linearized augmented plane wave (FLAPW) method. Indeed, significant progress has been achieved from advanced first-principles FLAPW calculations for the predictions of surface/interface magnetism. One recently resolved challenging issue is the role of noncollinear magnetism (NCM) that arises not only through the SOC, but also from the breaking of symmetry at surfaces and interfaces. For this, we will further review some specific advances we are witnessing today, including complex magnetic phenomena from noncollinear magnetism with no shape approximation for the magnetization (perpendicular MCA in transition-metal overlayers and superlattices; unidirectional anisotropy and exchange bias in FM and AFM bilayers; constricted domain walls important in quantum spin interfaces; and curling magnetic nano-scale dots as new candidates for non-volatile memory applications) and most recently providing new predictions and understanding of magnetism in novel materials such as magnetic semiconductors and multi-ferroic systems.     

Analogy between unconventional superconductivity and unconventional states of liquid crystals

An analogy is stressed between the order-parameter symmetries of the two-dimensional d-pairing wave superconductors and of liquid-crystal mesophases formed from achiral bent-shaped molecules. It leads to a definition of a class of liquid-crystal states which are the analogs of the unconventional superconducting states, and are characterized by a loss of discrete symmetry operations of the parent state.     

Cross-relaxation in multiple pulse NQR spin-locking

The experimental and theoretical NQR multiple-pulse spin locking study of cross-relaxation process in solids containing nuclei of two different sorts I?>?1/2 and S?=?1/2 coupled by the dipole–dipole interactions and influenced by an external magnetic field. Two coupled equations for the inverse spin temperatures of the both spin systems describing the mutual spin lattice relaxation and the cross-relaxation were obtained using the method of the nonequilibrium state operator. It is shown that the relaxation process is realized with non-exponential time dependence describing by a sum of two exponents. The cross relaxation time is calculated as a function of the multiple-pulse field parameters which agree with the experimental data. The calculated magnetization cross relaxation time vs the strength of the applied magnetic field agrees well with the obtained experimental data.     

Time reversal in two-frequency NQR methods

A theoretical treatment is carried out for the time reversal of nuclear quadrupole resonance signals for nuclear spin 5/2 and two-frequency action. Fiz. Tverd. Tela (St. Petersburg) 39, 1358–1359 (August 1997)