Spin Ordering and Thermodynamical Properties in Spin-Pair Systems under Magnetic Fields

It has recently been shown that in spin-pair systems a new type of spin ordering occurs under magnetic fields. In the present paper, the spin ordering in general cases of the inter-pair exchange interaction and the thermodynamical properties of these systems are investigated on the basis of molecular field theory. Various types of spin ordering appear depending on the strength of the inter-pair exchange interaction and the external magnetic field. The specific heat originating from the short range order of spins in a one-dimensional lattice is also calculated for a purpose of comparison with experiments in Cu(NO_3)_22.5H_2O

Spin Ordering in a Spin-Pair System

A new type of spin ordering in a spin-pair system is theoretically investigated. In the system, the intra-pair exchange interaction is antiferromagnetic and is much stronger than the inter-pair exchange interaction. In an external magnetic field, the excited triplet of the pair splits, and the lowest component of the triplet crosses the ground singlet at a certain magnitude of the field. In the vicinity of the point of level crossing, even the weak inter-pair exchange interaction causes a considerable amount of mixing between the singlet and the lowest component of the triplet. Due to the mixing, an ordering of the spin component perpendicular to the external field occurs. This ordering explains an anomaly which has been found by Haseda et al. in their experiment of cooling by adiabatic magnetization of Cu(NO_3)_22.5H_2O

Sound Attenuation in Magnetic Metals(Physics)

The anomalous sound attenuation due to spin fluctuations near the magnetic phase transition temperatures in itinerant magnets and the rare earth metals is theoretically studied. By applying Tsuneto and Kadanoff and Falko\u27s formulas, the attenuation coefficient is calculated. The calculated results explain the critical anomalies observed in magnetic metals such as Ni and Gd. By comparing the results with that for insulating magnets, the expression of the exchange striction is obtained. The effect of magnetic field on the critical attenuation is discussed

Short Range Order of Spins in Cu(NO_3)_22.5H_2O under Magnetic Field

In Cu(NO_3)_22.5H_2O, the Cu^ ions are coupled in almost isolated pairs by antiferromagnetic exchange interaction, and the pairs are considered to be linked in one-dimensional way by weak inter-pair exchange interaction. In an external magnetic field, the ground singlet of the pair crosses the lowest component of the excited triplet at about H=36kOe. In the vicinity of the point of level crossing, a large amount of the short range order of the spin component perpendicular to the field appears at sufficiently low temperatures. An anomaly found by Haseda et al. in their experiment of cooling by adiabatic magnetization of the crystal can be explained as the occurrence of this short range order

Coherent emission from disordered arrays of driven Josephson vortices

We propose a mechanism of coherent emission from driven vortices in stacked intrinsic Josephson junctions. In contrast to super-radiance, which occurs only for highly ordered vortex lattices, we predict resonant radiation emission from weakly correlated vortex arrays. Our analytical results for the THz wave intensity, resonance frequencies, and the dependence of THz emission power on dissipation are in good agreement with the ones obtained by recent simulations.Comment: 2 figure

Periods of Long Period Superlattices in Alloys

Domain sizes of long period superlattices in alloys are calculated by minimizing the ordering energy which mainly originates from the energy of conduction electrons. The domain size M thus obtained has a strong tendency to be fixed at integral numbers. This tendency explains the experimental results that the periods are fixed at M=2 in A_3B-type alloys, such as Au-Cd, Au-Zn, and Pd-Mn, independently of their electron-atom ratios. The anomalous dependence of M on the electron-atom ratio in the Ag-Mg alloy system is also explained

Spin-Triplet Vortex State in the Topological Superconductor CuxBi2Se3

We report on the observation of bulk superconductivity from dc magnetization measurements in a cylindrical single crystal of CuxBi2Se3. The magnitude of the magnetization in the Meissner state is very small and the magnetic-field dependence of the magnetization just above the lower critical field Hc1 is very different from those of usual type-II superconductors. We studied the character of the vortex state theoretically in a spin-triplet pairing superconductor and compared it with the experimental results. The results showed that, the superconductivity observed in CuxBi2Se3 is consistent with the spin-triplet pairing superconductivity with odd parity. We also observed a rapid relaxation phenomenon of the superconducting diamagnetism.Comment: 11 pages, 4 figures, to be published in PRB Rapid Communication