Nuclear spin-lattice relaxation in finely dispersed carbonizate powders

Finely dispersed carbonizate powders were studied with the aim of revealing their suitability for producing hyperpolarized noble gases. In the temperature and frequency dependences obtained over a wide range of temperatures and magnetic fields for the spin-lattice relaxation times of the magnetic moments of ³He, ¹H, and ¹³C nuclei, anomalous features caused by the suppression of the exchange between surface paramagnetic centers in a magnetic field were observed. It is shown that the interaction with magnetic moments of the ¹H nuclei situated near the paramagnetic centers is the main polarization-leakage channel for the noble-gas nuclear spins.     

Influence of interaction of phonons with a paramagnetic impurity on the strength properties of polymers

The strength characteristics of polymers with a paramagnetic impurity in an external magnetic field are considered. It is shown that because of spin-phonon interaction the strength of a polymer should grow with increasing magnetic field at low temperatures when mainly the lowest-lying spin levels are populated. The dependence of the increase in the strength on the magnetic field is different for Kramers and non Kramers ions. It is shown that an increase in the strength upon application of a magnetic field can be observed even for polymers and solids which are not paramagnetic in the unloaded state. This is because an external mechanical force initiates changes in the structure of the solid and, consequently, can give rise to paramagnetism in the system.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 83–87, June, 1984.     

On Magnetic Flux Trapping by Surface Superconductivity

The magnetic flux trapping by surface superconductivity is considered. The stability of the state localized at the cylindrical sample surface upon a change in the external magnetic field is tested. It is shown that as the magnetic field decreases, the sample acquires a positive magnetic moment due to magnetic flux trapping; i.e., the magnetization curve of surface superconductivity is “paramagnetic” by nature.     

High-temperature dynamics of surface magnetism in iron thin films

Finite-temperature magnetic properties of iron thin films are investigated by computer simulation over a broad range of temperatures up to the point of the ferromagnetic–paramagnetic phase transition. The coupled dynamics of atoms and magnetic moments is treated using the large-scale spin–lattice dynamics (SLD) algorithm. We investigate surface and bulk magnetic properties of iron, and how these properties vary as a function of temperature, film thickness and surface crystallography. We find that magnetization at surfaces is enhanced at low temperatures and suppressed at higher temperatures, in agreement with experimental observations. The effective Curie temperature of a film decreases as a function of thickness. Short-range magnetic order and non-vanishing spin–spin spatial correlations are found above the Curie temperature. The spin autocorrelation functions exhibit slower oscillations with longer decoherence times near the surface. We also find that the directional spin disorder has a significant effect on the surface strain.     

SU(3) Polyakov Linear-Sigma Model: Magnetic Properties of QCD Matter in Thermal and Dense Medium

The linear-sigma model, in which information about confining gluons is included through the Polyakov-loop potential (PLSM), is considered in order to perform a systematic study for various magnetic properties of QCD matter under extreme conditions of high temperatures and densities and finite magnetic field strengths. The introduction of magnetic field to the PLSM Lagrangian requires suitable utilization of Landau quantization, modification in the dispersion relations, and momentum-space dimension-reduction. We observed that increasing the magnetic field leads to filling-up lower Landau levels first and decreasing the number of occupied levels. We conclude that the population of Landau levels is most sensitive to the magnetic field and to the quark charges. The influences of finite magnetic field on the temperature dependence of chiral and deconfinement order-parameter(s) are studied. We present estimations for the magnetization, the magnetic susceptibility, the permeability, and the catalytic properties of QCD matter as functions of temperature. The dependences of the resulting freeze-out parameters, temperatures, and baryon chemical potentials on the corresponding magnetic field strengths have been analyzed, as well. These calculations are compared with recent lattice QCD simulations, whenever available. We conclude that the QCD matter seems to have paramagnetic property at temperatures greater than the critical one. There is an evidence for weak diamagnetic property at low temperatures. Last but not least, we observe that the magnetic catalysis is inverse, namely, the critical temperatures decrease with increasing the magnetic field.     

超交换作用对Er3Ga5O12的磁特性的影响

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Detection of vortex excitations in a Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10</Subscript> crystal at temperatures above the critical temperature by EPR of the surface layer

Vortex excitations have been detected at temperatures both below and above the critical temperature when investigating local magnetic fields on the surface of a Bi₂Sr₂Ca₂Cu₃O₁₀ single crystal by means of an electron paramagnetic resonance (EPR) probe. A thin layer of a diphenyl picrylhydrazyl organic radical deposited on the crystal surface is used as the EPR probe. A narrow EPR signal makes it possible to detect weak distortions of the magnetic field appearing at T ≿ T _c. The analysis of the temperature dependences of the resonance field and the EPR linewidth is thebasis of the assumption of the vortex nature of magnetic excitations in this temperature range.     

Anomalously strong relaxation of the polarization of muons in the magnetically ordered and paramagnetic states of the TbMnO<Subscript>3</Subscript> multiferroic

An anomalously strong relaxation of the muon polarization in a magnetically ordered state in the TbMnO₃ multiferroic has been revealed by the method below the μSR Néel temperature (42 K). Such a relaxation is due to the muon channel of relaxation of the polarization and the interaction of the magnetic moment of the muon with inhomogeneities of the internal magnetic field of an ordered state in the form of a cycloid. Above the Néel temperature, beginning with temperatures depending on the applied magnetic field, a two-phase state has been revealed where one phase has an anomalously strong relaxation of the muon polarization for a paramagnetic state. These features of the paramagnetic state are due to short-range magnetic order domains that appear in strongly frustrated TbMnO₃. A true paramagnetic state has been observed only at T ≥ 150 K.     

Linear-temperature dependence of static magnetic susceptibility in LaFeAsO from dynamical mean-field theory

In this Letter we report the local density approximation with dynamical mean field theory results for magnetic properties of the parent superconductor LaFeAsO in the paramagnetic phase. Calculated uniform magnetic susceptibility shows linear dependence at intermediate temperatures in agreement with experimental data. Contributions to the temperature dependence of the uniform susceptibility are strongly orbitally dependent. For high temperatures (>1000 K) susceptibility first saturates and then decreases with temperature. Our results demonstrate that linear-temperature dependence of static magnetic susceptibility in pnictide superconductors can be reproduced without invoking antiferromagnetic fluctuations.     

Magnetic structuring of electrodeposits

Metal electrodeposition reflects the pattern of the magnetic field at the cathode surface created by a magnet array. For deposits from paramagnetic cations such as Co2? or Cu2?, the effect is explained in terms of magnetic pressure which modifies the thickness of the diffusion layer, that governs their mass transport. An inverse effect allows deposits to be structured in complementary patterns when a strongly paramagnetic but nonelectroactive cation such as Dy3? is present in the electrolyte, and is related to inhibition of convection of water liberated at the cathode, in the inhomogeneous magnetic field. The magnetic structuring depends on the susceptibility of the electroactive species relative to that of the nonelectroactive background.     

Fermi surface of CeIn3 above the Néel critical field

We report measurements of the de Haas-van Alphen effect in CeIn(3) in magnetic fields extending to approximately 90 T, well above the Néel critical field of mu(0)H(c) approximately 61 T. The unreconstructed Fermi surface a sheet is observed in the high magnetic field polarized paramagnetic limit, but with its effective mass and Fermi surface volume strongly reduced in size compared to that observed in the low magnetic field paramagnetic regime under pressure. The spheroidal topology of this sheet provides an ideal realization of the transformation from a "large Fermi surface" accommodating f electrons to a "small Fermi surface" when the f-electron moments become polarized.     

Mössbauer spectroscopic study of a low temperature magnetic transition in ordered Fe-doped NiAl

Mössbauer spectroscopic (MS) measurements at ambient and cryogenic temperatures on powdered Fe-doped NiAl materials (Ni-40Al-9Fe and Ni-50Al-9Fe) exhibited paramagnetic behavior down to 17 K, with one Fe-site in the hosts. At 4.2 K, Ni-40Al-9Fe (Al deficient) remained paramagnetic, while Ni-50Al-9Fe (Ni deficient) displayed a magnetic transition, resolved in terms of one Fe environment. The internal magnetic field of the magnetically split site of Ni-50Al-9Fe was 185?±?8 kOe determined from a field distribution model. This shows that electronic and magnetic interactions in ordered Fe-doped NiAl depend on Fe site preference tendencies. The single Fe site observed at 4.2 K for the Ni-deficient alloy shows that its Fe distribution or site occupancy is not random but ordered. The interactions leading to the development of internal magnetic field in the Ni-deficient ordered alloy is temperature dependent being absent above 17 K based on MS measurements from ambient to 4.2 K.     

Fe-Cr-Co-Si永磁合金的磁性和穆斯堡尔效应研究

本文研究了成分为(重量百分比)65Fe-22Cr-12Co-1Si的可加工永磁合金。对高温淬火样品和经过磁场热处理及时效的样品,研究了饱和磁矩与温度的关系,以及室温和约80K的穆斯堡尔谱,计算了谱参数。实验表明:两种样品的磁性都随测量中热循环而改变。时效样品在室温除出现铁磁性相外,还出现顺磁性相;顺磁性相在低温下转变为铁磁性相。在时效样品中发现了磁矩的不完全的取向效应。最后讨论了这一材料的反磁化机制和提高矫顽力的途径。 关键词：     

The magnetotransport properties of the intermetallic compound GdCu6

We have studied the temperature and magnetic field dependence of the electrical resistivity of GdCu(6) and have co-related the results with the temperature dependence of heat capacity and magnetization. The magnetoresistance of GdCu(6) is found to be positive both in the paramagnetic and antiferromagnetic regimes. Within the antiferromagnetic regime, the magnetoresistance is very high and increases to still higher values both with increasing field and decreasing temperature. In the paramagnetic regime the magnetoresistance continues to exhibit a finite positive value up to temperatures much higher than that corresponding to the antiferromagnetic to paramagnetic phase transition. We have shown through quantitative analysis that both the temperature dependences of resistivity and heat capacity indicate the presence of spin fluctuations within the paramagnetic regime of GdCu(6). The field dependence of electrical resistivity indicates that the positive magnetoresistance in the paramagnetic phase is not related to the orbital motion of the conduction electrons in a magnetic field (the Kohler rule). In contrast, our analysis indicates that these spin fluctuations are responsible for the positive magnetoresistance observed within this paramagnetic regime. The nature of the field dependence of electrical resistivity is found to be qualitatively similar both in the antiferromagnetic and paramagnetic regimes, which probably indicates that spin fluctuations in the paramagnetic regime are of the antiferromagnetic type.     

Spin-dependent localization effects in GaAs:Mn/MnAs granular paramagnetic–ferromagnetic hybrids at low temperatures

We compare the magneto-transport in paramagnetic–ferromagnetic GaAs:Mn/MnAs granular hybrids and paramagnetic GaAs:Mn reference samples. The differences in the hole transport between the two systems at low temperatures arise due to carrier localization effects at the cluster–matrix interface in the hybrids. The localization is caused by a Schottky barrier formation at the interface as well as spin-dependent shifts of the hole bands caused by the stray field of the ferromagnetic clusters. The application of an external magnetic field leads to a delocalization of the carriers and thus a negative magneto-resistance effect. These effects can be simulated using a network model approach.     

Metamagnetic transition in Na 0.85 CoO2 single crystals

We report the magnetization, specific heat, and transport measurements of a high quality Na(0.85)CoO2 single crystal in applied magnetic fields up to 14 T. At high temperatures, the system is in a paramagnetic phase. It undergoes a magnetic phase transition below approximately 20 K. For the field H||c, the measurement data of magnetization, specific heat, and magnetoresistance reveal a metamagnetic transition from an antiferromagnetic state to a quasiferromagnetic state at about 8 T at low temperatures. However, no transition is observed in the magnetization measurements up to 14 T for H perpendicular c. The low temperature magnetic phase diagram of Na(0.85)CoO2 is determined.     

Probing the spin state of a single electron trap by random telegraph signal

We have studied the random telegraph signal (RTS) generated by a single paramagnetic spin center adjacent to a submicrometer silicon metal-oxide-semiconductor field-effect transistor. An in-plane magnetic field induces a substantial change in the statistics of the RTS. We show that a model using the grand partition theorem can qualitatively explain the change in statistics of the RTS as a function of the applied magnetic field. While the data at high temperatures can be well described by this simple model, quantitative discrepancy increases as the temperature is lowered.     

Evidence for spin freezing and ferromagnetic short-range correlations in57Fe-doped LiNiO2

Evidence for a frozen spin ground state and a mixed magnetic ordered and paramagnetic state at intermediate temperatures was found in⁵⁷Fe-doped LiNiO₂, using Mössbauer spectroscopy. The magnetic measurements, in agreement with Mössbauer data, suggest short-range ferromagnetic correlations at low temperatures and the occurrence of a paramagnetic phase below the spin freezing temperature.     

Fermi surface changes across the Néel phase boundary of NdB6

We report de Haas-van Alphen measurements in both the antiferromagetic and paramagnetic regimes of NdB6, which are shown to be separated by a second order upper critical field for antiferromagnetic ordering of H_{c} approximately 30 T when the magnetic field is parallel to [001]. The Fermi surface changes across the transition provide an ideal example of a system in which the effect of a one-dimensional magnetic periodic potential on doubling the unit cell (as originally predicted by Slater [Phys. Rev. 82, 538 (1951)]) can be tuned by varying only the magnetic field. The Fermi surface within the paramagnetic phase resembles that observed in other hexaborides such as LaB6 but with additional exchange splitting effects and weak correlations.