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Spin Glass (spin + glass)
Selected AbstractsGrowth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1,xCuxO6CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2006S. M. Rao Abstract Single crystals of Ba2PrRu1,xCuxO6 with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO-PbF2 in the temperature range 1100,1200 °C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1,2 mm across and 0.1,0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B2O3. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5,7 wt% solute concentration and 0.51 wt% of B2O3. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x-ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radiation amorphization of orthoferrite YFeO3PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2003Yu. G. Chukalkin Abstract Polycrystalline orthoferrite YFeO3 samples irradiated by fast neutron fluence 3 × 1024 m,2 were investigated by the X-ray and magnetic methods. It has been shown experimentally that the irradiation of the perovskite-structure oxide leads to its full amorphization and, as a consequence, to the magnetic transformation antiferromagnetic , spin glass. The authors believe that the amorphization is the consequence of the instability of the perovskite structure to radiation disordering. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Short-range ±J interaction Ising spin glass in a transverse field on a Bethe lattice: a quantum-spherical approachPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2006T. K. Kope Abstract We consider the short-range interaction disordered quantum Ising model with symmetric binary ±J bond distribution on the Bethe lattice (with coordination number z). The system exhibits quantum phase transition separating the spin glass and disordered phases where the quantum effect are regulated by a param- eter , describing the transverse field. By introducing a mapping of the quantum Hamiltonian of the model onto a soft-spin action we consider it truncated version in a form of the solvable quantized spherical model. Quantum dynamics is examined via various correlation functions on the infinite tree which are evaluated in a closed form. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic and transport properties of the Co-doped manganite La0.7Sr0.3Mn1,xCoxO3 (0 , x , 0.5)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2005B. C. Zhao Abstract The effect of Co doping on the magnetic and transport properties of La0.7Sr0.3Mn1,xCoxO3 (0 , x , 0.5) is investigated. The Co doping at Mn sites dilutes the double-exchange interaction between Mn3+ and Mn4+ ions and changes the long-range ferromagnetic (FM) order of La0.7Sr0.3MnO3 (LSMO) to the spin glass (SG) or cluster glass (CG) state for samples with x , 0.1. For x , 0.3, the paramagnetic (PM) metal to FM metal transition of LSMO disappears and the temperature dependence of resistivity ,(T) follows semiconducting behavior in the whole measured temperature region with the resistivity increasing by orders of magnitude. An interesting result is that ,(T) exhibits an obvious anomaly at T* , 100 K, which is ascribed to the spin-state transition of Co ions. For samples with x = 0.1 and 0.3, magnetoresistance (MR) effects are markedly enhanced in the low-temperature region compared with undoped LSMO, which is suggested to originate from the appearance of spin-dependent tunneling magnetoresistance. However, for samples with x = 0.5, the MR effect is suppressed over the entire temperature region measured and an obvious exchange anisotropy phenomenon, characterized by the shift of the hysteresis loop, is also observed, which is ascribed to the marked increase of the antiferromagnetic insulating phase. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of the Mn compositional distribution on the magnetic order in diluted GaMnN layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008D. Mai Abstract GaMnN is a prototypical GaN-based dilute magnetic semiconductor (DMS) and its potential as a room temperature ferromagnetic material is still a controversial question to be answered. Diluted GaMnN layers with Mn concentrations up to several percent have been grown by plasma-assisted MBE on MOVPE-GaN templates either on p-Si(111) or on Al2O3(0001) substrates. None of the samples reported here shows second phase precipitates in XRD or in the TEM analysis. However different composition distributions have been evidenced by EDX during the scanning TEM analysis. GaMnN grown at a substrate temperature of TS = 650 °C exhibits extended structural defects and strong compositional inhomogeneity. This could be indicative of decomposition due to local strain. Samples grown at TS = 775 °C with a Mn concentration of about 3% show a homogeneous Mn distribution in the layer. The magnetic properties are found to vary from spin glass to ferromagnetic behaviour at room temperature among different samples. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanostructured antiferromagnetic spin glass in doped Ge near the insulator,metal transitionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008A. G. Zabrodskii Abstract It is shown that, on the insulator side of the insulator , metal transition, the single spin density exponentially disappears as T , 0. Such spins are bound into pairs to give an antiferromagnetic (AFM) phase. Upon an increase in temperature the AFM phase is destroyed, the single-spin density, and, as a result, ESR absorption signal becomes stronger. The temperature dependencies of the densities of the pairs and single spins are typical of a chaotic distribution of neutral donors. In this case, there is no Neel temperature. In low degree of compensation, the crystal lattice of Ge with the AFM phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AFM phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Antiferromagnetic phase in doped semiconductors near the insulator,metal phase transitionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2006A. I. Veinger Abstract We show for n -type semiconductors, using Ge:As and 4H -SiC:N as examples, that the spin density measured by electron spin resonance (ESR) falls sharply near the insulator,metal (IM) transition. Two reasons might be responsible for this phenomenon: potential fluctuations with concentration of the electrons in local minima or local antiferromagnetic spin pairing ("spin glass") in the insulating state just below the IM transition. In the investigated semiconductors manifestation of the latter is observed as a change from Curie to a Curie,Weiss behaviour with negative constant ,. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hitting time of large subsets of the hypercubeRANDOM STRUCTURES AND ALGORITHMS, Issue 2 2008erný Abstract We study the simple random walk on the n -dimensional hypercube, in particular its hitting times of large (possibly random) sets. We give simple conditions on these sets ensuring that the properly rescaled hitting time is asymptotically exponentially distributed, uniformly in the starting position of the walk. These conditions are then verified for percolation clouds with densities that are much smaller than (n log n) -1. A main motivation behind this article is the study of the so-called aging phenomenon in the Random Energy Model, the simplest model of a mean-field spin glass. Our results allow us to prove aging in the REM for all temperatures, thereby extending earlier results to their optimal temperature domain. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2008 [source] | ||||||||||