40 research outputs found
Theoretical search for superconductivity in Sc3XB perovskites and weak ferromagnetism in Sc3X (X = Tl, In, Ga, Al)
A possibility for a new family of intermetallic perovskite superconductors
Sc3XB, with X = Tl, In, Ga and Al, is presented as a result of KKR electronic
structure and pseudopotential phonon calculations. The large values of computed
McMillan--Hopfield parameters on scandium suggest appearance of
superconductivity in Sc3XB compounds. On the other hand, the possibility of
weak itinerant ferromagnetic behavior of Sc3X systems is indicated by the small
magnetic moment on Sc atoms in two cases of X =~ l and In. Also the electronic
structure and resulting superconducting parameters for more realistic case of
boron--deficient systems Sc3XB_x are computed using KKR--CPA method, by
replacing boron atom with a vacancy. The comparison of the calculated
McMillan--Hopfield parameters of the Sc3XB series with corresponding values in
MgCNi3 and YRh3B superconductors is given, finding the favorable trends for
superconductivity.Comment: 13 pages, 13 figures. v3 - revise
Superconductivity of Mo3Sb7 from first principles
Superconductivity in Mo3Sb7 is analyzed using the combined electronic
structure and phonon calculations, and the electron--phonon coupling constant
\lambda_{ph}=0.54 is determined from first principles. This value explains the
experimental value of the superconducting critical temperature T_c=2.2 K. The
possible influence of spin fluctuations and spin gap on the superconductivity
in Mo3Sb7 is discussed, and electron--paramagnon interaction is found to be
weak.Comment: 4 pages, 4 figures. To be published in Phys. Rev.
Electronic structure, magnetism and spin fluctuations in the superconducting weak ferromagnet Y4Co3
Results of the first principles study on the electronic structure and
magnetism of the superconducting weak ferromagnet YCo, are presented.
Using the full potential Korringa-Kohn-Rostoker (FP-KKR) method, densities of
states, dispersion curves and magnetic moments were calculated for
quasi-ordered structural model of the compound in the framework of the local
density approximation. Spin-polarized KKR calculations confirm that weak
ferromagnetic properties of YCo can be attributed to only one cobalt
atom located on (2b) site in the unit cell, while other twenty Co and Y atoms
acts as a diamagnetic environment. Moreover, the magnetic Co atoms form a
quasi-one-dimensional chains along direction. The magnitude of Co(2b)
magnetic moment () markedly overestimates the experimental value
(0.23~), which suggests the importance of spin fluctuations in this
system. Calculated distribution of spin magnetization in the unit cell provides
a background for discussion of the coexistence of ferromagnetism and
superconductivity in YCo. Finally, the effect of pressure on magnetism
is discussed and compared with experimental data, also supporting weak
ferromagnetic behaviors in the system.Comment: 10 pages, 10 figures, To be published in Phys. Rev.
Giant magnetocaloric effect in Mn 1-t (Ti 0.5 V 0.5 ) t as compounds near room temperature
International audienceMn 1-t (Ti 0.5 V 0.5) t As compounds with t varying from 0 to 0.20 were synthesised by arc melting and subsequently annealed. The X-ray diffraction analysis reveals pure and fairly crystallised samples. Magnetisation measurements show that the Curie temperature decreases to room temperature with t the substitution rate. The sharp and abrupt character of the 1 st order transition of MnAs-type turns to a less marked variation of the magnetic entropy in the vicinity of the transition temperature, profit made to a wider temperature range of MCE efficiency