摘要:

The kinetics of isotopic phase separation of3He–4Hesolid mixtures for various molar volumes has been studied by precision pressure measurements at a constant volume. It is found that the attainment of equilibrium between coexisting phases formed as a result of stratification is described correctly by an exponential dependence for various modes of crystal cooling and heating. The characteristic phase separation time decreases with temperature, thus confirming the athermal quantum nature of the growth of a new phase during the phase transition. The phase separation time is found to increase considerably with crystal pressure. It is shown that the prevailing theory can provide only a qualitative description of the established regularities. A quantitative description of experimentally observed decay times requires an analysis of diffusion processes in a gas of impurity excitations in the presence of a concentration gradient. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593661

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The range of applied magnetic fieldHcorresponding to the stability of mixed state with a fixed magnetic inductionBis determined for a high-TcsuperconductingYBa2Cu3Oxsingle crystal forH⊥c-axis. For this purpose, the field dependences of the contribution&mgr;vto the dynamic magnetic permeability&mgr;ac′are analyzed for the hysteresis loops&mgr;v(H)in the temperature range from 70 to 84 K. It is shown that the&mgr;v(H)hysteresis can be interpreted in terms of the interaction between the vortex lattice and the surface and is associated with theB(H)hysteresis as a manifestation of the Bean–Livingston surface barrier. As a result, the&mgr;v(H)hysteresis loops corresponding to different temperatures can be described by a universal curve in dimensionless coordinates. The obtained estimates and the available experimental data reveal a significant suppression of the surface barrier in actual YBaCuO single crystals as compared to the barrier predicted for a perfect surface. The lower branch of the&mgr;v(H)hysteresis loop, which corresponds to increasingH,is found to be close to the equilibrium&mgr;v(H)curve, and the surface barrier appreciably affects the behavior of&mgr;v(H)only for decreasing field, i.e., the emergence of magnetic vortices from the sample surface. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593647

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is shown that a consistent analysis of the nonlocal interlayer exchange in semi-confined metallic magnetic superlattice of the ferromagnet–nonmagnetic metal type with antiferromagnetic coupling between ferromagnetic layers leads to the formation of new types of collective dipole–exchange spin-wave excitations near the surface of the magnetic superlattice. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593648

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A compensated ferro–antiferromagnet interface is studied in the framework of a discrete classical spin model. The phase diagram is presented for the possible collinear and canted magnetic structures of the interface. The change in magnetization upon a transition from a collinear structure to canted form is studied. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593649

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is shown by using the exact quantum-mechanical solution that a one-dimensional antiferromagnetic Heisenberg spin chain is unstable to the emergence of an easy-plane magnetic anisotropy in a real three-dimensional crystal. It is shown that the magnetic anisotropy is due to a Jahn–Teller type effect, i.e., a strong spin–lattice coupling. A change in the equilibrium position of ligands induces magnetic anisotropy in the spin chain. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593650

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Experimental results of investigations of monocrystalline samples ofHg1−x−yCrxMnySesolid solution indicate, first, a considerable influence of manganese atoms introduced inHg1−xCrxSeon the absolute values of physical parameters such as magnetic susceptibility, phase-transition temperature, mobility of conduction electrons, and the period of time during which the samples go over to the equilibrium state, and second, the formation of materials with improved electrophysical and clearly pronounced magnetic characteristics as compared withHg1−xCrxSesamples with the same concentration of chromium ions. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593651

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The formation and the growth dynamics of 180°-domains in ferroelectrics in external field are investigated with the use of the statistical approach within the Ginzburg–Landau model. It is shown that despite the polarizing role of an external field the formation of an intermediate polydomain structure is found to be more preferable than immediate transfer to the monodomain ordering state. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593652

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is shown that in addition to equal-module exchange structures satisfying the criterion for the existence of the Andreev–Marchenko and Bar’yakhtar–Yablonskii spin scalar, other equal-module exchange structures also exist. In contrast to the structures obtained from the condition for the existence of a spin scalar, the latter follow from thermodynamic conditions and correspond to thermodynamically stable phases. Besides, these structures are not related to the restrictions imposed on the dimensionality of irreducible representation typical of the structures of the former kind. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593653

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The surfaces corresponding to the loss of stability and equilibrium of paramagnetic and antiferromagnetic states are found in the mean field approximation with temperature, field, and anisotropy as variables. The characteristic temperatures at which the topology of phase diagram sections changes are determined. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593654

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is stated that an electron can be in a state localized at an intercrystallite or twin boundary or stacking fault irrespective of the specific structure of the transition region. It is important that the crystal containing such a boundary must be non-periodic “as a whole.” The one-dimensional model (two abutting Kronig–Penney lattices for which the spectrum of localized states is determined) is considered. The bands containing one or two discrete levels alternate in a complex way in the spectrum. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593655

出版商:AIP    

年代:1998

数据来源: AIP