scholarly journals SPECIFIC HEAT OF Mg11B2 IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3180-3183
Author(s):  
R. A. FISHER ◽  
F. BOUQUET ◽  
N. E. PHILLIPS ◽  
D. G. HINKS ◽  
J. D. JORGENSEN
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Specific Heat ◽  
Normal State ◽  
Energy Gap ◽  
Zero Magnetic Field ◽  
Energy Gaps ◽  
State Electron ◽  
Electron Contribution ◽  
Semi Empirical

We present specific-heat measurements on Mg 11 B 2 in magnetic fields to 9 T. The anomaly at Tc is rapidly broadened and attenuated in fields, as expected for an anisotropic, randomly oriented superconductor. At low temperature there is a strongly field-dependent feature that shows the existence of a second energy gap. The Sommerfeld constant, γ, increases rapidly and non-linearly with magnetic field, which cannot be accounted for by anisotropy. It approaches γn = 2.6 mJ K -2 mol -1, the coefficient of the normal-state electron contribution, asymptotically for fields greater than 5 T. In zero magnetic field the data can be fitted with a phenomenological two-gap model, a generalization of a semi-empirical model for single-gap superconductors. Both of the gaps close at the same Tc; one is larger and one smaller than the BCS weak coupling limit, in the ratio ~ 4:1, and each accounts for ~ 50% of the normal-state electron density of states. The parameters characterizing the fit agree well with those from theory and are in approximate agreement with some spectroscopic measurements.

scholarly journals MAGNETOCALORIC EFFECT AND HEAT CAPACITY OF MAGNETIC FLUIDS

2020 ◽  
Vol 63 (5) ◽  
pp. 12-18
Author(s):  
Viktor V. Korolev ◽  
Anna G. Ramazanova ◽  
Olga V. Balmasova ◽  
Matvey S. Gruzdev
Keyword(s):  
Magnetic Field ◽  
Heat Capacity ◽  
Magnetic Fields ◽  
Specific Heat ◽  
Magnetocaloric Effect ◽  
Specific Heat Capacity ◽  
Magnetic Fluids ◽  
Zero Magnetic Field ◽  
Extreme Character ◽  
Temperature Dependences

The magnetic fluids based on magnetite nanoparticles were synthesized using mixed surfactants (oleic acid/alkenyl succinic anhydride) dispersed in different carrier media (polyethylsiloxane and dialkyldiphenyl). The physicochemical properties of magnetic fluids (density, viscosity, saturation magnetization, magnetic phase concentration, magnetic core size) were determined. Magnetic fluids are stable in a wide temperature range. All the samples of the magnetic fluids exhibit typical superparamagnetic behavior. The magnetocaloric effect and the specific heat capacity of the magnetic fluids were first direct determined at 288–350 K in a magnetic field of 0–1.0 T. The field dependences of the magnetocaloric effect have a classic linear form. The temperature dependences of the magnetocaloric effect of magnetic fluids in magnetic fields have an extreme character. Thermodynamic parameters of magnetic fluids (magnetization namely enthalpy/entropy change) were determined. The specific heat capacity of magnetic fluid samples in a zero magnetic field was obtained at different temperatures (at 278–350 K) on a differential scanning calorimeter and on the original microcalorimeter. The temperature dependences of the heat capacity of magnetic fluids in magnetic fields have an extreme character. It was established that the difference in heat capacity values obtained in and without the magnetic field is within the experimental error. The extreme character of the heat capacity is reflected in the magnetocaloric effect temperature dependences.

Magnetic phases in UNi2Si2

Open Physics ◽  
2004 ◽  
Vol 2 (2) ◽  
Author(s):  
Pavel Svoboda ◽  
Pavel Javorský ◽  
Fuminori Honda ◽  
Vladimír Sechovský ◽  
Alois Menovsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Diffraction ◽  
Thermodynamic Properties ◽  
Specific Heat ◽  
Magnetic Phase ◽  
Uniaxial Anisotropy ◽  
Magnetic Phase Transitions ◽  
Zero Magnetic Field ◽  
Direction Parallel

AbstractThe tetragonal compound UNi2Si2 exhibits in zero magnetic field three different antiferromagnetic phases belowT N=124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q z). Two additional order-order magnetic phase transitions are observed below T N, namely atT 1=108 K and T 2=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi2Si2 single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi2Si2.

UPPER CRITICAL FIELD OF UNCONVENTIONAL SUPERCONDUCTORS FROM CHEMICAL EQUILIBRIUM

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3443-3448 ◽  
Author(s):  
A. KALLIO ◽  
J. HISSA ◽  
T. HÄYRYNEN ◽  
V. BRÄYSY
Keyword(s):  
Magnetic Field ◽  
Critical Field ◽  
Normal State ◽  
Chemical Equilibrium ◽  
Critical Density ◽  
Upper Critical Field ◽  
Universal Function ◽  
Zero Magnetic Field ◽  
Mathematical Treatment ◽  
Critical Fields

We have shown previously that many normal state properties of high Tc superconductors in zero magnetic field can be understood in terms of a single universal function f(t) in the scaled variable t=T/T*, where T* is connected with temperature independent gap 2Δ=2kBT*, which gives the binding energy of a pair in analogy with dissociation of molecules. The function f(t) determines the fraction of bosons (B++) and fermions (h+) at temperature T and it is obtained from the mathematical treatment of chemical equilibrium with respect to the reaction B++⇌ 2h+. Since for magnetic fields of reasonable strength the Zeeman energy is much smaller than the pseudo gap Δ~100K-800K, the function f(t) in the normal state is largely independent of magnetic field. The main effect of the magnetic field is to increase the tendency for bosons to localize. This means that the critical density nL for delocalization in the ab-plane direction and the critical density for superfluidity nc (≳ nL) both increase with magnetic field. This causes the corresponding temperatures TBL(H) and Tc(H) to go down with the field. Assuming a power law dependence nc(H)/nc(0)=1+AHμ, the upper critical fields for several heavy fermion compounds are shown to fall into a single curve. The purpose here is to show that the upper critical field Hc2(y) (y=Tc(H)/Tc(0)) can be expressed in a simple way in terms of f(t). We show that this theory predicts all the shapes of Hc2(y) observed in several unconventinal superconductors such as Tl 2 Ba 2 CuO 6+δ, with Tc=15 K.

Point-contact spectroscopy probing the NbSe3 CDW gap in different crystallographic orientations

2002 ◽  
Vol 12 (9) ◽  
pp. 119-122
Author(s):  
A. A. Sinchenko ◽  
P. Monceau
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Applied Magnetic Field ◽  
Energy Gap ◽  
Point Contact ◽  
Point Contacts ◽  
Energy Gaps ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
Crystallographic Orientations

We have measured the differential current-voltage characteristics of normal metal-NbSe3 direct point contacts (without insulating barrier) formed along different crystallographic orientations under applied magnetic field with different orientations. At low temperature two energy gaps, $\Delta_{p1}$ and $\Delta_{p2}$, corresponding to the high and the low-temperature CDW were observed simultaneously as a singulanty of the excess resistance which is attributed to an analog of Andreev reflection, in which the incident electron reflects on the Peierls energy gap barriers with its charge unchanged. An applied magnetic field up to 8.5 T does not lead to a change in the density of states and in the Peierls energy gaps, suggesting that the large magnetoresistance observed in NbSe3 might not result from the change in the CDW order parameter with magnetic field but rather from the increase of scattering of non-condensed to CDW carriers.

Specific heat of Sm0.55Sr0.45MnO3 manganite in magnetic fields up to 15 T: An anomalous critical behavior of the ferromagnet in magnetic field and the observation of a tricritical point

JETP Letters ◽  
2006 ◽  
Vol 84 (1) ◽  
pp. 31-34 ◽  
Author(s):  
Sh. B. Abdulvagidov ◽  
A. M. Aliev ◽  
A. G. Gamzatov ◽  
V. I. Nizhankovskiĭ ◽  
H. Mödge ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Specific Heat ◽  
Critical Behavior ◽  
Tricritical Point

ELECTRON AND HOLE EFFECTIVE g FACTORS IN InAs/GaSb QUANTUM WELLS

2003 ◽  
Vol 02 (06) ◽  
pp. 437-444 ◽  
Author(s):  
A. ZAKHAROVA ◽  
S. T. YEN ◽  
K. A. CHAO
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Quantum Wells ◽  
Landau Level ◽  
Heavy Hole ◽  
Strong Dependence ◽  
Zero Magnetic Field ◽  
Electron Level ◽  
Hole Level ◽  
G Factors

We investigate the Landau level structures and the electron and hole effective g factors in InAs / GaSb quantum wells under electric and quantizing magnetic fields perpendicular to interfaces. In these structures, the lowest electron level in InAs can be below the highest heavy-hole level in GaSb at zero magnetic field B. Thus the electron and hole levels anticross with the increasing magnetic field and the strong dependence of the Landau level structures as well as g factors on B is obtained. We have found that the voltage across the structure and the lattice-mismatched strain also produce the essential changes in the Landau level structures as well as the electron and hole g factors.

Mössbauer study of the Ni–Zn ferrite system

1970 ◽  
Vol 48 (4) ◽  
pp. 381-396 ◽  
Author(s):  
J. M. Daniels ◽  
A. Rosencwaig
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Full Range ◽  
Zinc Content ◽  
Zero Magnetic Field ◽  
Nickel Zinc ◽  
Zn Ferrite ◽  
Superparamagnetic Clusters ◽  
Ferrite System ◽  
Nuclear Magnetic

Mössbauer spectra of 57Fe in the nickel–zinc ferrite system (ZnO)x(NiO)1−xFe2O3 have been obtained, at room temperature and at 77 °K, in zero magnetic field and also in a longitudinal magnetic field of 13.5 kG, covering the full range of zinc content. The dependence of the isomer shifts, line widths, quadrupole interactions, and nuclear magnetic fields of 57Fe3+ ions in both tetrahedral and octahedral sites has been determined. The principal results of this study are (a) the confirmation of the determination of the nuclear magnetic fields by Abe et al. using NMR, and the extension of these measurements to higher zinc concentrations, (b) an indication that the hypotheses of paramagnetic centers, proposed by Gilleo, and superparamagnetic clusters, proposed by Ishikawa, are not applicable to the nickel–zinc ferrites, (c) evidence of canted spin structures, first proposed by Yafet and Kittel, (d) various effects of chemical disorder in the nickel-zinc ferrites, and (e) an observation of the effect on the Mössbauer spectrum of relaxation in a magnetically ordered iron system.

HIGH-FIELD TRANSPORT PROPERTIES OF T'-Ln2-xCexCuO4 (Ln=Nd, Pr, La)

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3216-3219 ◽  
Author(s):  
T. SEKITANI ◽  
N. MIURA ◽  
M. NAITO
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Magnetic Fields ◽  
Transport Properties ◽  
Normal State ◽  
Low Temperatures ◽  
High Field ◽  
Magnetic Moments ◽  
Negative Magnetoresistance ◽  
High Magnetic Fields

We report low-temperature magnetotransport in the normal state of the electron-doped superconductors, Nd 2-x Ce x CuO 4, Pr 2-x Ce x CuO 4, and La 2-x Ce x CuO 4, by suppressing the superconductivity with high magnetic fields. The normal state ρ-T curve shows an up-turn at low temperatures, which has a log T dependence with saturation at lowest temperatures. The up-turn is gradually suppressed with increasing magnetic field, resulting in negative magnetoresistance. We discuss these findings on the basis of the Kondo scattering originating from the magnetic moments of Cu 2+ ions.

scholarly journals Non-local terahertz photoconductivity in the topological phase of Hg1−xCdxTe

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. S. Kazakov ◽  
A. V. Galeeva ◽  
A. I. Artamkin ◽  
A. V. Ikonnikov ◽  
L. I. Ryabova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Laser Pulses ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Topological Phase ◽  
Non Local ◽  
Dark Signal ◽  
The Magnetic Field

AbstractWe report on observation of strong non-local photoconducitivity induced by terahertz laser pulses in non-zero magnetic field in heterostructures based on Hg1−xCdxTe films being in the topological phase. While the zero-field non-local photoconductivity is negligible, it is strongly enhanced in magnetic fields ~ 0.05 T resulting in appearance of an edge photocurrent that exceeds the respective dark signal by orders of magnitude. This photocurrent is chiral, and the chirality changes every time the magnetic field or the electric bias is reversed. Appearance of the non-local terahertz photoconductivity is attributed to features of the interface between the topological film and the trivial buffer.

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