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1.
The existence of a remanent magnetization (M
rem) on switching off the field of a field cooled (FC) sample of a highT
c superconductor is often reported. It has recently been argued thatM
rem should equal the difference in FC and zero field cooled (ZFC) magnetizations (M
FC —M
ZFC) in hard superconductors and this has been demonstrated to hold in single crystals of YBCO at 4.2K over a limited range ofH values. We report the detailed magnetization measurements under various thermomagnetic histories (of whichM
rem is one special case) on two specimens of Nb, which show different extents of flux trapping. We find that there are in general
three regions inH, T space, corresponding toM
rem+M
ZFC−M
FC=0,M
rem<(M
FC−M
ZFC) andM
rem>(M
FC−M
ZFC). At anyT, the equality holds forH<H
c1(T), and forH→H
c2 (M
FC−M
ZFC) asymptotically vanishes and thereM
rem>(M
FC−M
ZFC). We show that there exists an intermediate region in all hard superconductors, whereM
rem<(M
FC−M
ZFC). The range over which this situation persists, however, depends on the degree of irreversibility in a sample. We can explain
qualitatively all the history dependent magnetization data in terms of the critical state model. We point out an inconsistency
in an earlier analysis to determineH
c1(T) from such data in YBCO. We also propose a new criterion for putting limits onH
c1(T) in hard superconductors. 相似文献
2.
A comparison has been made of irreversibility temperature determined by four different methods in few specimens of lead (type-I)
and niobium (type-II). The merger ofM
ZFC(T) andM
FC(T) curves giveT
r(H) values lower than those evident from vanishing the hysteresis in isothermal DC magnetization. The identification of peak
temperature inx″
H
(T) data withT
r(H) is appropriate only if the contribution from changes in the normal state electrodynamics can be isolated and the peak is
narrow. The appearance of differential paramagnetic effect inx′
H
(T) data is adequate to imply reversibility, however, its efficacy to precisely locate irreversibility line remains to be established. 相似文献
3.
D. A. Balaev A. A. Dubrovskiĭ S. I. Popkov K. A. Shaĭkhutdinov M. I. Petrov 《Physics of the Solid State》2008,50(6):1014-1021
The hysteresis of magnetoresistance R(H) and relaxation of the remanent resistance R rem with time after magnetic field treatment of HTSC (Y-Ba-Cu-O) + CuO composites are studied. Such a composite constitutes a network of Josephson junctions wherein the nonsuperconducting component (CuO) forms Josephson barriers between HTSC grains. By comparing the experimental R rem(t) and R(H) dependences, it is shown that the relaxation of the remanent resistance is caused by the decreased magnetic field in the intergrain medium due to relaxation of magnetization. The reason is uncovered for the differences between the published values of pinning potentials determined by measuring the relaxation of magnetization or resistance and fitting them by the Anderson law. 相似文献
4.
S. Shamaila R. Sharif S. Riaz M. Khaleeq-ur-Rahman X. F. Han 《Applied Physics A: Materials Science & Processing》2008,92(3):687-691
Co
x
Pt1−x
(x≥0.7) alloy nanowires are grown into self-synthesized anodic alumina templates by electrodeposition. Magnetic and magnetization
properties of Co
x
Pt1−x
alloy nanowires are measured as functions of wire length, temperature, and field orientation. X-ray diffraction shows that
as-prepared CoPt nanowires are of fcc polycrystalline structure. A crossover of easy axis of magnetization is observed from
parallel to perpendicular of the nanowire axis as a function of length. The coercivity (H
c) and remanent squareness (SQ) of Co
x
Pt1−x
nanowire arrays are derived from hysteresis loops measured at various angles (θ) between the field and wire axis. H
c(θ) and SQ(θ) curves show bell-shaped or otherwise bell-shaped behavior corresponding to the easy axis of their magnetization. 相似文献
5.
Ugur Topal 《Physica B: Condensed Matter》2012,407(12):2058-2062
In the present study, the effects of B2O3 addition on the remanence properties of barium ferrite magnets are examined. The relationship between isothermal magnetization remanence MR(H) and demagnetization remanence MD(H) for non-interacting single domain particles, MD(H)=MR(Hmax)−2MR(H), was used in order to investigate the interactions between particles. We have found that remanence magnetization MR increased by 40% in magnitude with B2O3 addition in addition to the weakened couplings between particles. The B2O3 addition seems to supply the required conditions for usage of these materials in the magnetic recording media. 相似文献
6.
Magnetic flux trapping (MFT) in granular YBa2Cu3O7 − δ high-temperature superconductors (HTSCs) is studied. At T = 77.36 K, the dependence of the hysteresis of the transverse magnetoresistance on transport current I and the maximum value of external magnetic field H
ext is found in the measurement cycle 0 → H
extmax → 0. The dependences of the parameters characterizing MFT, namely, residual magnetoresistance, field H
min at which the magnetoresistance is minimal, and the magnetoresistance at H
ext = H
min, on I and H
extmaxare determined. MFT is found to occur in HTSC granules under the action of an external magnetic field exceeding the lower
critical field of superconducting granules H
c1A, and the transport current only weakly affects the magnitude of MFT. 相似文献
7.
S. Sarkar A. D. Thakur C. V. Tomy G. Balakrishnan D. McK Paul S. Ramakrishnan A. K. Grover 《Pramana》2006,66(1):193-207
New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM(H) (∞ critical current densityJ
c(H)) in isothermalMH scans in a weakly pinned single crystal of Ca3Rh4Sn13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles
of vortices injected through the sample edges towards the destined equilibrium vortex state at a givenH. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence inJ
c(H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state
between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of
Ca3Rh4Sn13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the
onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point
and a critical point in the (H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light
of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb. 相似文献
8.
Adolfo Franco Thiago Eduardo Pereira Alves Emília Celma de Oliveira Lima Eloisa da Silva Nunes Vivien Zapf 《Applied Physics A: Materials Science & Processing》2009,94(1):131-137
For the first time nanocrystalline magnetic particles of Mg
x
Fe(3−x)O4 with x ranging from 0.5 to 1.5 have been synthesized by a combustion reaction method using iron nitrate Fe(NO3)3.9H2O, magnesium nitrate Mg(NO3)2.6H2O, and urea CO(NH2)2 as fuel without intermediate decomposition and/or calcining steps. X-ray diffraction patterns of all systems showed broad
peaks consistent with cubic inverse spinel structure of MgFe2O4. The absence of extra reflections in the diffraction patterns of as-prepared materials ensures the phase purity. The mean
crystallite sizes determined from the prominent (311) peak of the diffraction using Scherrer’s equation and transmission electron
microscopy micrographs were c.a. 40 nm with spherical morphology. Fourier transform infrared spectra of the as-prepared material
showed traces of organic and metallic salt by-products; however, these could be removed by washing with deionized water. Typical
hysteresis curves were obtained for all specimens in magnetic field up to 14 T between 4 and 340 K. The saturation magnetization
was 48.3 emu/g and 31.3 emu/g, 44.8 emu/g, and 28.4 emu/g for x=1.0 and 0.8 at 4 K and 340 K, respectively. The saturation magnetization, M
s
, of nanoparticles of the MgFe2O4 specimen is about 50% higher when compared to the bulk. The enhanced magnetization measured in our nanoparticles MgFe2O4 specimens may be attributed to the uncompensated magnetic moment of iron ions between the A- and B-sites, i.e., changes in
the inversion factor. Our magnetization results of MgFe2O4 specimens are comparable to the existing data for the same compound but with different particle size and prepared by different
synthesis methods. 相似文献
9.
The character of the evolution of a system of weak links in granular high-temperature superconductors under the action of
an external magnetic field H
ext has been studied by measuring the current-voltage characteristics E(j)Hext = constE{(j)_{{H_{ext}} = const}} of YBa2Cu3O7 − δ (δ ≈ 0.05) ceramic samples. The measurements have been performed at T = 77.3 K in a range of very weak magnetic fields 0 < H
ext ≲ 0.5H
c2J, where H
c2J is the upper critical field of the Josephson weak links. The results have been used to construct the field dependences of
the magnetoresistance Δρ(H
ext) of the superconducting ceramics. It has been established that the parameters of the power equation E = A(j − j
cJ)ν and the magnetoresistance Δρ are nonmonotonic functions of the external magnetic field. The presence of extrema in the curves
A(H
ext), j
cJ(H
ext), ν(H
ext), and Δρ(H
ext) indicates that different systems of weak links between grain boundaries, which are capable of forming extended Josephson
contacts, undergo sequential transitions to a resistive state with an increase in H
ext. 相似文献
10.
A. V. Korolev M. I. Kurkin O. B. Sokolov N. B. Orlova 《Physics of the Solid State》2010,52(3):561-567
The dependences of the magnetization M and the magnetic susceptibility χ = ∂M/∂H of pure gadolinium (the concentration of foreign impurities is lower than 0.1 wt %) on the temperature T and the magnetic field H have been measured using a Quantum Design MPMS-5XL SQUID magnetometer. In this material, inhomogeneities of the atomic structure
should not lead to a nonuniform distribution of the magnetic characteristics (including the Curie temperature T
C) over the volume of the sample. The obtained dependences of M and χ have been used to investigate the possibility of suppressing magnetic inhomogeneities of other types by magnetic fields
with a strength of up to 50 kOe. It has been assumed that these inhomogeneities are suppressed when the specific relationship,
namely, the 21/3 rule is fulfilled. The rule relates the portions of the dependence χ(T, H) which at the temperature T = T
C and at the maximum in the curve χ(T) (T = T
m
) depend on H in accordance with the H
2/3 law. It has been shown that the portions separated from the experimental curves χ(T
C, H) and χ(T
m
, H) obey the 21/3 rule. 相似文献
11.
Magnetic experiments are powerful tools to study fundamental properties and to check the qualities of samples. Temperature, stress, and impurities of materials can all affect magnetic properties and play an important role in the utilization of these materials for engineering applications. The estimation and analysis of the spontaneous magnetization can reveal ferromagnetic particles as impurities in samples. The shape of the temperature dependence of magnetization is indicative of the origin of the magnetic properties. However, it is necessary to correlate the χ
m
(T) curves and isothermal M(H) plots to achieve a complete analysis of the electronic properties of the materials. Highlights of magnetic properties of lithium intercalation compounds are briefly described. Intrinsic and extrinsic properties are considered as useful parameters to determine the purity of electrode materials for rechargeable Li-ion batteries. 相似文献
12.
Y. Kopelevich V. V. Lemanov S. Moehlecke J. H. S. Torres 《Physics of the Solid State》1999,41(12):1959-1962
Measurements of the basal-plane resistivity ρ
a(T,H) performed on highly oriented pyrolitic graphite, with magnetic field H∥c-axis in the temperature interval 2–300K and fields up to 8 T, provide evidence for the occurrence of both field-induced and
zero-field superconducting instabilities. Additionally, magnetization M(T,H) measurements suggest the occurrence of Fermi surface instabilities which compete with the superconducting correlations.
Fiz. Tverd. Tela (St. Petersburg) 41, 2135–2138 (December 1999) 相似文献
13.
14.
Results are presented of an investigation of the magnetic properties of dilute frustrated ferrimagnetic spinels Li0.5Fe2.5−x
GaxO4 (x=0.8–1.2), which characterize the main parameters of the ferrimagnetic state and provide evidence of local violation of collinear
spin ordering and frustrations. In particular, measurements were made of the concentration dependences of the magnetic moment
n
0(x) and the Curie point T
c
(x), the magnetization isotherms σ
T
(H) at T=4.2 K and H⩽10 kOe, and also the low-and high-field magnetization polytherms σ
H
(T). It was established that for x⩾0.8 in fields exceeding the technical saturation field H
s
∼2 kOe, the temperature dependences of the high-field magnetization σ
H
(T) between 4.2 and 230 K cannot be described by the Bloch T
3/2 law whereas this law is satisfied for undiluted Li spinel (x=0). Over the entire temperature range (4.2–230 K) the experimental curves σ
H
(T) may be approximated by σ
H
(T)=σ
0(1−AT
3/2 − BT
5/2) for x=0.8–1.0 and σ
H
(T)=σ
0[1−CT
3/2exp(μ(H−H
0)/k
B
T)] for x=1.1, 1.2, where μH
0∼15 K is the internal field produced by competition between exchange interactions and frustrations.
Fiz. Tverd. Tela (St. Petersburg) 40, 1075–1079 (June 1998) 相似文献
15.
R. Z. Levitin A. S. Markosyan A. B. Petropavlovskii V. V. Snegirev 《Physics of the Solid State》1997,39(10):1633-1635
Measurements of magnetization in static fields up to 60 kOe and magnetic susceptibility in weak ac fields of the Y(Ni1−x
Mx)3 and Y2(Ni1−x
Mx)7 intermetallics (M=Fe and Cu, x
max=0.2), as well of the specific heat of these systems for some compositions are reported. It was found that these intermetallics
are ferromagnetic at low temperature, and that their spontaneous magnetizations M
s at 4.2 K and Curie temperatures T
C decrease monotonically with increasing copper concentration. The magnetic susceptibility of the Y(Ni1−x
Fex)3 system with 0.06≲x≲0.2 was observed to decrease rapidly with the temperature lowered below a characteristic temperature T
s. One of possible reasons for such an anomaly is shown to be the onset in this concentration region of the reentrant spin-glass
state at low temperatures. The results obtained demonstrate that the tight-binding d-band model fails to explain the evolution of the magnetic properties of YNi3 and Y2Ni7 in the case of small substitutions of iron and copper for nickel.
Fiz. Tverd. Tela (St. Petersburg) 39, 1828–1830 (October 1997) 相似文献
16.
D. A. Balaev A. A. Dubrovskiy S. I. Popkov K. A. Shaikhutdinov O. N. Mart’yanov M. I. Petrov 《Journal of Experimental and Theoretical Physics》2010,110(4):584-593
The transport properties (R(T) and R(H) dependences at various values of the transport current in magnetic fields up to 65 kOe) and low-temperature heat capacity
in magnetic fields up to 90 kOe of the BaPb0.75Bi0.25O3 superconductor (T
C
≈ 11.3 K) are investigated with the goal of clarifying the mechanisms determining the nonmonotonic behavior and hysteresis
of its magnetoresistance R(H). The type of R(H) hysteretic dependences for BaPb0.75Bi0.25O3 is analogous to that observed in granular high-T
c
superconductors (HTSCs); however, unlike classical HTSC systems, the field width of the magnetoresistance hysteresis loop
for polycrystalline BaPb0.75Bi0.25O3 depends on the transport current. This means that although the mechanisms responsible for the magnetoresistance hysteresis
(the influence of the magnetic flux trapped in superconducting regions on the effective field in Josephson interlayers) are
identical in these objects, the transport current in BaPb0.75Bi0.25O3 may considerably affect the diamagnetic response of the superconductor. A considerable effect of transport current on the
field in which the R(H) dependences have a peak and exhibit hysterestic properties is observed. Such a behavior can be adequately interpreted using
the model of the spatially inhomogeneous superconductor-insulator state proposed by Gorbatsevich et al. [JETP Lett. 52, 95 (1990)]. The nonmonotonic dependence of quantity C/T (C is the heat capacity) on the magnetic field discovered in the present study also agrees with the conclusions based on this
model. 相似文献
17.
B. I. Belevtsev V. B. Krasovitsky D. G. Naugle K. D. D. Rathnayaka Glenn Agnolet I. Felner 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(8):1049-1052
Magnetic and superconducting properties of polycrystalline samples of RuSr2Gd1.5Ce0.5Cu2O(10 − δ), asprepared (by solid-state reaction) and annealed in pure oxygen at different pressure are presented. Specific heat and
magnetization were investigated in the temperature range 1.8–300 K with a magnetic field up to 8 T. Specific heat, C (T), shows a jump at the superconducting transition (with onset at T ≈ 37.5 K) and a Schottky-type anomaly below 20 K. It is found that curves C(T) taken for different values of magnetic field have the same crossing point (at T
* ≈ 2.7 K) for all samples studied. At the same time, C(H) curves taken for different temperatures have a crossing point at a characteristic field H
* ≈ 3.7 T. These effects are manifestations of the crossing-point phenomenon, which is supposed to be inherent for strongly
correlated electron systems. 相似文献
18.
Shailendra Kumar G Ravikumar P K Mishra P Chaddah B A Dasannacharya Ram Prasad N C Soni 《Pramana》1990,34(4):279-287
We have studied the variation of low field magnetization hysteresis in YBa2Cu3O7 as a function of the maximum magnetic field applied during a hysteresis cycle (1 G<H
max<7.3 G) and also as a function of temperature (77 K<T<95 K). The remnant magnetization is studied as a function ofH
max andT and the measured dependences are explained using the extended critical state model. The potential of this technique as a
contactless method of probing the temperature dependence ofJ
c is discussed. 相似文献
19.
A comparative investigation of the magnetic properties of amorphous nanogranular composites (Co41Fe39B20)
x
(SiO
n
)100 − x
and (Co86Nb12Ta2)
x
(SiO
n
)100 − x
has been performed in the subpercolation region at temperatures in the range 4.2–300 K. The thermomagnetic dependences in
the range 4.2–300 K and the processes of magnetization reversal and remanent magnetization relaxation at liquid-helium temperatures
have been studied. It has been established that the average anisotropy constants of amorphous nanograins are equal to 3.6–7.0
kJ/m3 for the (Co41Fe39B20)
x
(SiO
n
)100 − x
composites and 5–8 kJ/m3 for the (Co86Nb12Ta2)
x
(SiO
n
)100 − x
composites. The fundamental differences in the concentration dependences of the anisotropy constant K
eff and the coercive force H
C
have been revealed for the two systems under investigation. It has been demonstrated that, as the concentration of the metal
phase increases, the quantities K
eff and H
C
increase for the (Co86Nb12Ta2)
x
(SiO
n
)100 − x
composites and decrease for the (Co41Fe39B20)
x
(SiO
n
)100 − x
composites. 相似文献
20.
H. Kachkachi D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):291-300
Analytical calculations based on finite-size spin-wave theory and Monte Carlo (MC) simulations are performed to investigate
the validity of the well-known relation m(H, T) = M(H, T)B
D[M(H, T)
H/T] between the induced magnetization m of the magnetic particle and its intrinsic magnetization M for the Ising and isotropic classical models (B
D(x) is the Langevin function, D is the number of spin components, is the number of atoms in the particle). It follows from general arguments and from our analytical results for the Heisenberg
model at T≪T
c that this relation is not exact for any finite D and nonzero temperature. Nevertheless, corrections to this formula remain very small practically in the whole range T < T
c if ≫ 1, as confirmed by our Monte Carlo calculations. At T
T
c/4 there is a good agreement between the MC and finite-size spin-wave calculations for the field dependence of m and M for the Heisenberg model with free boundary conditions.
Received 1st December 2000 相似文献