scholarly journals ON DISCOVERY OF THE FERROMAGNETIC SUPERCONDUCTOR UCoGe

2011 ◽  
Vol 14 (2) ◽  
pp. 21-28
Author(s):  
Huy Thanh Nguyen ◽  
Cuong Duc Dao ◽  
Thu Thanh Vu ◽  
An Tu Bui
Keyword(s):  
Transition Temperature ◽  
Curie Temperature ◽  
Ambient Pressure ◽  
Spin Fluctuations ◽  
Resistive Transition ◽  
Unconventional Superconductor ◽  
Present Evidence ◽  
Microscopic Scale ◽  
Weak Ferromagnet ◽  
Curie Temperature Tc

We report the coexistence of ferromagnetic order and superconductivity in UCoGe at ambient pressure. The data obtained from the basic thermal, magnetic and transport properties on the macro and microscopic scale show that UCoGe is a weak ferromagnet with a Curie temperature TC = 3 K, and also, is a superconductor with a resistive transition temperature Ts = 0.8 K. Those present evidence that UCoGe is an unconventional superconductor and argue that superconductivity is mediated by critical ferromagnetic spin fluctuations.

scholarly journals An efficient control of Curie temperature TC in Ni–Mn–Ga alloys

2004 ◽  
Vol 272-276 ◽  
pp. 2067-2068 ◽  
Author(s):  
V.V. Khovailo ◽  
V.A. Chernenko ◽  
A.A. Cherechukin ◽  
T. Takagi ◽  
T. Abe
Keyword(s):  
Curie Temperature ◽  
Efficient Control ◽  
Curie Temperature Tc

scholarly journals Effect of Ca-substitution on the Magnetic and Dielectric Properties of Mn-Zn Ferrites

2012 ◽  
Vol 4 (2) ◽  
pp. 297 ◽  
Author(s):  
M. M. Rahman ◽  
P. K. Halder ◽  
F. Ahmed ◽  
T. Hossain ◽  
M. Rahaman
Keyword(s):  
Dielectric Constant ◽  
Curie Temperature ◽  
Loss Tangent ◽  
Sintering Temperature ◽  
Initial Permeability ◽  
Q Factor ◽  
Dielectric Polarization ◽  
Ca Substitution ◽  
Magnetic And Dielectric Properties ◽  
Curie Temperature Tc

Spinel Mn-Zn ferrites with composition MnxZn0.4Ca0.6-2xFe2+xO4, where x = 0.10, 0.15, 0.20, 0.25 and 0.30 have been prepared by conventional ceramic technique sintered at    1300 °C for 4 hours. The influence of Ca-substitution on various properties of Mn-Zn ferrites have been studied in this work. Investigations were carried out by the measurements of Curie temperature, permeability, loss tangent, Q-factor, dielectric constant and AC resistivity of the samples. Curie temperature (Tc), the real part of initial permeability (µ´), loss tangent (tan ?), and AC resistivity have been found to be decreased while the Q-factor increases with the increase in Ca-content. The frequency characteristics of the dielectric constant and AC resistivity have been found to be decreased as the frequency increases. Maxwell-Wagner interfacial type of dielectric polarization was observed with the addition of Ca-content over the entire range of frequency considered. Keywords: Spinel ferrites; Sintering temperature; Initial permeability; Dielectric constant.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i2.9752 J. Sci. Res. 4 (2), 297-306 (2012)

The temperature dependence of the photoinduced soft mode in Sn2P2S6 crystal

2019 ◽  
Vol 33 (08) ◽  
pp. 1950061
Author(s):  
K. A. Brekhov ◽  
N. A. Ilyin ◽  
E. D. Mishina ◽  
P. A. Prudkovskii ◽  
G. Kh. Kitaeva
Keyword(s):  
Phase Transition ◽  
Femtosecond Laser ◽  
Curie Temperature ◽  
Temperature Dependence ◽  
Oscillation Frequency ◽  
Phonon Mode ◽  
Soft Mode ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Curie Temperature Tc

In this paper, we present the results of the temperature dependence studies of the photoinduced phonon mode which appears in a ferroelectric-semiconductor Sn2P2S6 (SPS) crystal under the influence of femtosecond laser pulses. We show that its behavior reminds the soft mode one near the phase transition. However, the observed decrease in the oscillation frequency in the vicinity of Curie temperature Tc is much weaker than previously reported. This can be explained by the shadowing of the pure soft mode by its interaction with other photoinduced modes.

scholarly journals Research Progress on Ni-Based Antiperovskite Compounds

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
P. Tong ◽  
Y. P. Sun
Keyword(s):  
Phase Diagram ◽  
Transition Temperature ◽  
Single Crystals ◽  
Superconducting Transition Temperature ◽  
Spin Fluctuations ◽  
Research Progress ◽  
Future Research ◽  
Magnetic Element ◽  
Superconducting Transition ◽  
Cubic Structure

The superconductivity in antiperovskite compound MgCNi3was discovered in 2001 following the discovery of the superconducting MgB2. In spite of its lower superconducting transition temperature (8 K) than MgB2(39 K), MgCNi3has attracted considerable attention due to its high content of magnetic element Ni and the cubic structure analogous to the perovskite cuprates. After years of extensive investigations both theoretically and experimentally, however, it is still not clear whether the mechanism for superconductivity is conventional or not. The central issue is if and how the ferromagnetic spin fluctuations contribute to the cooper paring. Recently, the experimental results on the single crystals firstly reported in 2007 trend to indicate a conventionals-wave mechanism. Meanwhile many compounds neighboring to MgCNi3were synthesized and the physical properties were investigated, which enriches the physics of the Ni-based antiperovskite compounds and help understand the superconductivity in MgCNi3. In this paper, we summarize the research progress in these two aspects. Moreover, a universal phase diagram of these compounds is presented, which suggests a phonon-mediated mechanism for the superconductivity, as well as a clue for searching new superconductors with the antiperovskite structure. Finally, a few possible scopes for future research are proposed.

Magnetic Properties and Magnetostriction of ZnxNi1-x MnSb Alloys

2005 ◽  
Vol 475-479 ◽  
pp. 1715-1718
Author(s):  
S.K. Ren ◽  
G.B. Ji ◽  
Song Ling Huang ◽  
Q.Q. Cao ◽  
Feng Ming Zhang ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Curie Temperature ◽  
Structural Phase ◽  
Solid State Reaction Method ◽  
Experimental Result ◽  
Xrd Pattern ◽  
Zn Concentration ◽  
Magnetostriction Coefficient ◽  
The Relationship ◽  
Curie Temperature Tc

We have investigated the magnetic properties and magnetostriction of ZnxNi1-xMnSb compounds prepared by solid state reaction method. It is found that for x less than 0.6 the magnetization of ZnxNi1-xMnSb almost remains unchanged. However, when x is larger than 0.6 the magnetization starts to drop linearly. Experimental result indicates that at low Zn concentrations, x < 0.7, the Curie temperature (TC) decreases with increasing Zn concentration x. However, when x > 0.7, the Curie temperature increases distinctly with increasing x. The Zn concentrartion dependence of magnetostrictive ceofficient is also studied. The experimental curve shows that when x < 0.6 the value of magnetostriction coefficient for ZnxNi1-xMnSb decreases linearly with the increasing Zn concentration x. However, when x is above 0.6, the magnetostrictive ceofficient raises distinctly. By analyzing the XRD pattern, the structures of the materials are examined and the relationship between the properties and the structures are discussed. A structural phase transition is observed. It has been indicated that the structure plays an important role in the magnetic and magnetostrictive properties of the system.

scholarly journals Evidence for a pressure-induced antiferromagnetic quantum critical point in intermediate-valence UTe2

2020 ◽  
Vol 6 (42) ◽  
pp. eabc8709 ◽  
Author(s):  
S. M. Thomas ◽  
F. B. Santos ◽  
M. H. Christensen ◽  
T. Asaba ◽  
F. Ronning ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Applied Pressure ◽  
Quantum Critical Point ◽  
Antiferromagnetic Order ◽  
Intermediate Valence ◽  
Ac Calorimetry ◽  
Unconventional Superconductor ◽  
Spin Triplet ◽  
Magnetic States ◽  
Low Pressures

UTe2 is a recently discovered unconventional superconductor that has attracted much interest because of its potentially spin-triplet topological superconductivity. Our ac calorimetry, electrical resistivity, and x-ray absorption study of UTe2 under applied pressure reveals key insights on the superconducting and magnetic states surrounding pressure-induced quantum criticality at Pc1 = 1.3 GPa. First, our specific heat data at low pressures, combined with a phenomenological model, show that pressure alters the balance between two closely competing superconducting orders. Second, near 1.5 GPa, we detect two bulk transitions that trigger changes in the resistivity, which are consistent with antiferromagnetic order, rather than ferromagnetism. Third, the emergence of magnetism is accompanied by an increase in valence toward a U4+ (5f2) state, which indicates that UTe2 exhibits intermediate valence at ambient pressure. Our results suggest that antiferromagnetic fluctuations may play a more substantial role on the superconducting state of UTe2 than previously thought.

Magnetic, Electronic - and Magneto - Transport Properties of Nanocrystalline Nd0.6Sr0.4MnO3 Manganites

2009 ◽  
Vol 67 ◽  
pp. 131-136 ◽  
Author(s):  
Kundu Sourav ◽  
Kumar Nath Tapan
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Transition Temperature ◽  
Curie Temperature ◽  
Transport Properties ◽  
Significant Variation ◽  
Insulator Transition ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Low Field

We have reported in this paper, the effect of grain size in Nd0.6Sr0.4MnO3 .We have investigated the effect of grain size on metal-insulator transition and Curie temperature. We have also reported here the variation of low field magnetoresistance with temperature and grain size. We have observed that the Curie temperature increases monotonically with particle size. The metal insulator transition temperature initially increases with particle size and then gets fixed to a certain value. In these Nd0.6Sr0.4MnO3 nanometric systems, any significant variation of magnetoresistance with particle size is not observed.

METALLIC FERROMAGNETISM DRIVEN BY PHONON-ENHANCED SPIN FLUCTUATIONS

2007 ◽  
Vol 21 (06) ◽  
pp. 857-869
Author(s):  
JE HUAN KOO ◽  
GUANGSUP CHO
Keyword(s):  
Transition Temperature ◽  
Exchange Interactions ◽  
Spin Fluctuations ◽  
Electron Interaction ◽  
Sum Rule ◽  
Order Of Magnitude ◽  
High Transition ◽  
Strong Exchange ◽  
Normal States ◽  
Metallic Ferromagnetism

We investigate the metallic ferromagnetism for materials with incomplete 3d-orbitals. The ferromagnetism occurs in electrons of s-orbitals by phonon-enhanced spin flippings of d-electrons via s-d exchange interactions, which was discussed by us [Phys. Rev. B61, 4289 (2000)]. We know the electron-electron interaction, U sd , mediated by phonon-enhanced spin flippings is repulsive for metallic ferromagnetic materials but attractive for high transition temperature superconductors (HTSC). The electron-electron interaction, U sd , is an order of magnitude stronger than that by Kondo-type bare spin-flippings. We elucidate non-occurrence of ferromagnetism in Pd even though it has very strong exchange interactions. We also show that the charge sum rule is recovered in the case of inclusion of U sd . We calculate the resistivity in normal states.

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