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1.
Structural, electrical and magnetic measurements, as well as electron spin resonance (ESR) spectra, were used to characterise the single-crystalline CuCr1.6V0.4Se4 spinel and study the correlation between the negative magnetoresistance effect and magnon excitations. We established the ferromagnetic order below the Curie temperature T C ≈ 193 K, a p-type semiconducting behaviour, the ESR change from paramagnetic to ferromagnetic resonance at T C, a large ESR linewidth value and its temperature dependence in the paramagnetic region. Electrical studies revealed negative magnetoresistance, which can be enhanced with increasing magnetic field and decreasing temperature, while a detailed thermopower analysis showed magnon excitations at low temperatures. Spin–phonon coupling is explained within the framework of a complex model of paramagnetic relaxation processes as a several-stage relaxation process in which the V3+ ions, the exchange subsystem and conduction electron subsystem act as the intermediate reservoirs. 相似文献
2.
V.A. Stephanovich 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):17-21
We predict the existence of a Griffiths phase in dielectrics with a concentrational crossover between dipole glass (electric
analog of spin glass) and ferroelectricity. Particular representatives of the above substances are KTaO3:Li, Nb, Na, or relaxor ferroelectrics like Pb1–xLaxZr0.65Ti0.35O3. Since this phase exists above the ferroelectric phase-transition temperature (but below that temperature for ordered substances),
we call it a “para-glass phase”. We assert that the difference between paraelectric and para-glass phases in the above substances
is the existence of clusters (inherent to the “ordinary” Griffiths phase of Ising magnets) of correlated dipoles. We show
that randomness plays a decisive role in the Griffiths (para-glass) phase formation: this phase does not exist in a mean field
approximation. To investigate the Griffiths phase properties, we calculate the density of Yang-Lee (YL) zeros in the partition
function and find that it has “tails” inherent to the Griffiths phase in the above temperature interval. We perform calculations
on the basis of our self-consistent equation for the long-range order parameter in an external electric field. This equation
has been derived in the framework of the random field theory. The latter automatically incorporates both short-range (due
to indirect interaction via transverse optical phonons of the host lattice) and long-range (ordinary dipole-dipole) interactions between impurity dipoles,
so that the problem of long-range interaction considerations does not appear in it.
Received 17 May 2000 相似文献
3.
4.
The complex ac dynamic magnetic susceptibility was used to study the influence of temperature on critical fields in polycrystalline ZnCr2Se4 spinel. An antiferromagnetic order with a Néel temperature TN=20.7 K and a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θCW=55.1 K were established. An increasing static magnetic field shifts TN to lower temperatures while a susceptibility peak at Tm in the paramagnetic region—to higher temperatures. The non-zero and negative values both of the second and third harmonics of susceptibility suggest only a parallel spin coupling in ferromagnetic clusters in the range between the Néel and Curie-Weiss temperatures. Below TN the magnetic field dependence of susceptibility, χac(H), shows two peaks at critical fields Hc1 and Hc2. The values of Hc1 decrease slightly with temperature while the values of Hc2 drop rapidly with temperature. The strong changes of Hc2 temperature induced are mainly responsible for a spin frustration of the re-entrant type in the spinel under study. 相似文献
5.
N. G. Fazleyev 《Hyperfine Interactions》1990,60(1-4):691-694
The magnetic resonance lineshape of paramagnetic ion-nuclei in metals is calculated using the temperature Green functions
method and is analyzed for limiting cases of fast and slow spin lattice relaxation of localized moments. The longitudinal
spin lattice relaxation rate for paramagnetic ion-nuclei in type II superconductors due to the hyperfine coupling with local
moments is calculated. The influence of the fluctuation coupling of electrons on relaxation of paramagnetic ion-nuclei in
“dirty” type II superconductors is investigated in magnetic field slightly above the upper critical field Hc2. 相似文献
6.
C. Djurberg K. Jonason P. Nordblad 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):15-21
Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn)
spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the
underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature
is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding
behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation.
Received 27 October 1998 and Received in final form 30 November 1998 相似文献
7.
Zero field μSR has been used to probe rare earth spin dynamics in the magnetic superconductors, Y1−x
Er
x
Ni2B2C. The muon spin relaxation function is stretched exponential, exp (−(λt)β), in form, as usually found for spin glass systems above the glass temperature. However, the Y1−x
Er
x
Ni2B2C compounds show no evidence of coexisting superconducting and static spin glass ground states even at concentrations below
the critical value (x=0.6) for long range antiferromagnetic order. The temperature dependence of both the muon spin relaxation rate λ and the exponent
β suggests that Er spin dynamics change significantly at the superconducting transition temperature.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
8.
A.A. Zvyagin D.M. Apal'kov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):565-569
We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice.
We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg
antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic
field and nonzero temperature onto such a phase transition are studied.
Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998 相似文献
9.
N. UryÛ 《Phase Transitions》2013,86(1-4):133-175
Abstract Following the Bogoliubov variational principle, the equilibrium and stability equations of the free energy for the two sublattice antiferromagnetic system with inter- and intrasublattice exchange interactions and with an external magnetic field are investigated. For the Ising spin system with uniaxial anisotropy, the phase diagrams have been calculated for various values of anisotropy constant d and the ratio of intra- to intersublattice interaction constants γ. It is shown that first-order, as well as second-order transitions, occur for γ > 0, whereas only a second-order transition occurs for γ ≦ 0, irrespective of the sign of d. Furthermore, similar calculations are extended for the anisotropic Heisenberg spin system and quite interesting phase diagrams have been obtained. Next, the effects of the anisotropic exchange interactions on the magnetic ordered states and the magnetizations of the singlet ground state system of spin one and with a uniaxial anisotropy term are investigated in the vicinity of the level crossing field H ? D/gμ B . A field-induced ordered state without the transverse component of magnetization is shown to appear in a certain range of magnetic field as the spin dimensionality decreases. It has also turned out that the phase transition between this ordered state and the canted antiferromagnetic state ordinarily found for the isotropic singlet ground state system is of first order. Lastly, the stable spin configurations at a temperature of absolute zero for a two-sublattice uniaxial antiferromagnet under an external magnetic field of arbitrary direction are studied. In particular, the effects of a single ionic anisotropy D-term and anisotropy in the exchange interactions on the magnetic phases are investigated. The antiferromagnetic state has turned out to appear only for the external magnetic field along the easy axis of sublattice magnetization, and makes a first-order phase transition to the canted-spin state or the ferromagnetic state. For other field directions, no antiferromagnetic state appears and only a second-order phase transition between the canted-spin and the ferromagnetic states occurs. The critical field as a function of external field direction has been calculated for several D-values. 相似文献
10.
V. I. Al’shits E. V. Darinskaya O. L. Kazakova E. Yu. Mikhina E. A. Petrzhik 《JETP Letters》1996,63(8):668-673
A magnetic induction threshold B
c above which the magnetoplastic effect — depinning of dislocations from paramagnetic pinning centers — can be observed in
samples placed in a magnetic field is predicted and observed in Al, NaCl, and LiF crystals. The existence of a threshold is
associated with the fact that for B<B
c the spin-lattice relaxation time τsl in a dislocation-paramagnetic-center system is less than the time required for spin evolution in a magnetic field resulting
in the removal of the spin forbiddenness of an electronic transition that “switches off” the dislocation-pinning-center interaction.
It is shown that the threshold field B
c is sensitive to temperature and x-ray irradiation of the samples. A new method for measuring the spin-lattice relaxation
time in paramagnetic centers on dislocations is proposed on the basis of the data obtained.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 628–633 (25 April 1996) 相似文献
11.
Finite-size rounding of a first-order phase transition is studied in “block”- and “cylinder”-shaped ferromagnetic scalar spin
systems. Crossover in shape is investigated and the universal form of the rounded susceptibility peak is obtained. Scaling
forms on the low-temperature side of the critical point are considered both above and below the borderline dimensionality,d
>=4. A method of phenomenological renormalization, applicable to both odd and even field derivatives, is suggested and used
to estimate universal amplitudes for two-dimensional Ising models atT=Tc. 相似文献
12.
Nd0.75Na0.25MnO3 polycrystalline ceramic is prepared via sol-gel process and its magnetic properties and electron spin resonance (ESR) spectra have been investigated experimentally. As the compound is cooled from room temperature, a charge-ordered state first develops below 170 K. A high magnetic field melts the charge ordered state and stabilizes a ferromagnetic (FM) state below 170 K. A field induced transition, analogous to a spin flip transition, is observed between 40 and 170 K. The critical temperature for spin flip increases with increasing temperature. Below 130 K, the compound tends to be intrinsically inhomogeneous, i.e. FM clusters and paramagnetic domains coexist in this system at least, which is confirmed by ESR measurements. When the external magnetic field is zero, long range FM interaction is not developed in this system; however, a tendency of re-entrant FM transition is observed in this compound. 相似文献
13.
Peculiarities of ferromagnetic resonance (FMR) corresponding to bias along the “hard” magnetic axis of a film with 2D uniaxial
anisotropy are studied based on numerical solution of magnetic moment dynamics equations. It is shown that an additional resonance
peak is formed in the FMR spectrum in the vicinity of “bistability field” H
b
. The dependence of this field on the amplitude of the microwave field and damping parameters is analyzed. 相似文献
14.
We present results of LDA calculations (band structure, densities of states, Fermi surfaces) for possible iron based superconductor
BaFe2Se3 (Ba123) in normal (paramagnetic) phase. Results are briefly compared with similar data on prototype BaFe2As2 and (K,Cs)Fe2Se2 superconductors. Without doping this system is anti-ferromagnetic with T
Nexp ∼ 250 K and rather complicated magnetic structure. Neutron diffraction experiments indicated the possibility of two possible
spin structures (antiferromagnetically ordered “plaquettes” or “zigzags”), indistinguishable by neutron scattering. Using
LSDA calculated exchange parameters we estimate Neel temperatures for both spin structures within the molecular field approximation
and show τ1 (plaquettes) spin configuration to be more favorable than τ2 (zigzags). 相似文献
15.
T. A. Ivanova O. A. Turanova I. V. Ovchinnikov B. Andgheevskii M. Augustyniak-Jablokow 《Applied magnetic resonance》2011,40(1):21-30
The temperature dependence of electron paramagnetic resonance (EPR) spectra of a series of dithiocarbamates Fe(RR′dtc)3 was studied in the temperature range from 5 to 300 K. A small part of solvated complexes serving as spin probes in the EPR-silent
matrix enabled the observation of EPR of the Fe(III) ion in the whole temperature range. The spin transition was revealed
in the reduction of the integral intensity of the signal from the high-spin complexes and in the non-monotonous change of
the line width with temperature decrease due to the effect of the low-spin complexes with short spin–lattice relaxation times.
Below ca. 60 K, the ferromagnetic ordering of the magnetic moments in low-spin particles (“domains”) arising at the spin transition
was observed. 相似文献
16.
N. A. Babushkina A. N. Taldenkov A. V. Kalinov L. M. Fisher O. Yu. Gorbenko J. Rohrkamp T. Lorenz D. I. Khomskii K. I. Kugel 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(10):1345-1347
The oxygen isotope effect was investigated in cobalt oxides (Pr1 − y
Eu
y
)0.7Ca0.3CoO3 (0.12 < y < 0.26). The measurements of magnetization, electric resistivity, differential magnetic susceptibility, thermal expansion,
and specific heat show that as the Eu concentration increases, a transition from “ferromagnetic metal” to “weakly magnetic
insulator” is observed at y ≈ 0.18. In the insulating ground state, the transition occurs with a Co spin-state change that is suppressed in the ferromagnetic
(FM) metallic phase. The spin-state transition at y > 0.18 is accompanied by a substantial oxygen isotope effect that is virtually absent in the FM phase (y < 0.18). 相似文献
17.
A. I. Dmitriev R. B. Morgunov S. V. Zaitsev 《Journal of Experimental and Theoretical Physics》2011,112(2):317-326
The static and high-frequency dynamic magnetic properties and photoluminescence of two-dimensional semiconductor GaAs heterostructures
containing an InGaAs quantum well and a thin manganese layer (δ layer) are studied. It is found that the Curie temperature
is T
C ≈ 35 K and the magnetic anisotropy field of the ferromagnetic manganese δ layer is H
a ≈ 600 Oe. The spin resonance spectrum exhibits a line in weak fields (from −50 to 100 Oe), which is observed in the same
temperature interval T < 40 K where the ferromagnetic ordering of the manganese δ layer occurs. This line is probably caused by the nonresonance
contribution of the spin-dependent scattering of charge carriers to the negative magnetic resistance. The dependence of the
degree of polarization of photoluminescence on the magnetic field also points to the ferromagnetic behavior of the manganese
δ layer. 相似文献
18.
Chiral and racemic molecular ferrimagnets [MnII(HL)(H2O)][MnIII(CN)6] · 2H2O, where L = S-or R-1,2-diaminopropane for chiral samples (S-pn, R-pn) and L = rac-pn for racemic samples, are investigated by the electron spin resonance technique. It is revealed that the electron spin resonance
spectra of the chiral and racemic samples differ from each other at temperatures below the Curie temperature T
C = 21 K. The maximum in the temperature dependence of the integrated magnetic susceptibility χ(T) calculated by the double integration of the line centered at a negative field of −250 Oe for the racemic samples is broadened
as compared to the maxima in the corresponding dependences for the enantiomers of the chiral samples with “right” (R) and “left” (S) symmetry. The new compounds under investigation differ from the previously synthesized crystals by the strong spin-orbit
interaction between Mn3+ ions, which leads to a dependence of their magnetic properties on the chirality of the structure.
Original Russian Text ? R.B. Morgunov, F.B. Mushenok, M.V. Kirman, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50,
No. 7, pp. 1252–1256. 相似文献
19.
V. E. Arkhipov V. E. Startsev V. P. Dyakina J. Klamut Ya. M. Mukovskii A. Czopnik 《JETP Letters》1998,68(1):42-46
Magnetization measurements were performed on a lanthanum manganite La0.9Sr0.1MnO3 single crystal in the temperature interval 4.2–300 K and magnetic field interval 50 Oe-55 kOe in two sample cooling regimes:
1) cooling down to 4.2 K in a high (55 kOe) magnetic field, and 2) cooling in a “zero” field. It is shown that the temperature
dependences of the magnetization M(T) are substantially different in these regimes. Pronounced anomalies of M(T) were observed at temperatures T*=103 K and T
c
=145 K. The first anomaly is attributed to a structural transition, while the second one corresponds to a ferromagnet-paramagnet
phase transition. The magnetization of a La0.9Sr0.1MnO3 single crystal in the cooling regimes studied shows typical “spin-glass” behavior.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 39–43 (10 July 1998) 相似文献
20.
We study the effect of quantum fluctuations in an Ising
spin system on a scale-free network of
degree exponent γ>5 using
a quantum Monte Carlo simulation technique. In our model,
one can adjust the magnitude of the magnetic field perpendicular
to the Ising spin direction and can therefore control the
strength of quantum fluctuations for
each spin. Our numerical analysis
shows that quantum fluctuations reduce the transition
temperature Tc of the ferromagnetic-paramagnetic phase
transition. However, the phase transition belongs to
the same mean-field type universality class both with
and without the quantum fluctuations.
We also study the role of hubs by turning on the
quantum fluctuations exclusively
at the nodes with the most links. When only a small number of hub
spins fluctuate quantum mechanically, Tc
decreases with increasing magnetic field
until it saturates at high fields. This effect
becomes stronger as the number of hub spins increases.
In contrast, quantum fluctuations at the same number of
“non-hub” spins do not affect Tc. This implies
that the hubs play an important role in
maintaining order in the whole network. 相似文献