2 research outputs found
Detailed electronic structure studies on superconducting MgB and related compounds
In order to understand the unexpected superconducting behavior of MgB
compound we have made electronic structure calculations for MgB and closely
related systems. Our calculated Debye temperature from the elastic properties
indicate that the average phonon frequency is very large in MgB compared
with other superconducting intermetallics and the exceptionally high in
this material can be explained through BCS mechanism only if phonon softening
occurs or the phonon modes are highly anisotropic. We identified a
doubly-degenerate quasi-two dimensional key-energy band in the vicinity of
along -A direction of BZ which play an important role in
deciding the superconducting behavior of this material. Based on this result,
we have searched for similar kinds of electronic feature in a series of
isoelectronic compounds such as BeB, CaB, SrB, LiBC and
MgBC and found that MgBC is one potential material from the
superconductivity point of view. There are contradictory experimental results
regarding the anisotropy in the elastic properties of MgB ranging from
isotropic, moderately anisotropic to highly anisotropic. In order to settle
this issue we have calculated the single crystal elastic constants for MgB
by the accurate full-potential method and derived the directional dependent
linear compressibility, Young's modulus, shear modulus and relevant elastic
properties. We have observed large anisotropy in the elastic properties. Our
calculated polarized optical dielectric tensor shows highly anisotropic
behavior even though it possesses isotropic transport property. MgB
possesses a mixed bonding character and this has been verified from density of
states, charge density and crystal orbital Hamiltonian population analyses
Competing magnetic structures and magnetic transitions in Er2Ni2Pb Powder neutron diffraction measurements
We have studied the magnetic structures of Er2Ni2Pb using a powder neutron diffraction technique in zero field. Previous bulk measurements suggested three distinct magnetic phase transitions. Our neutron diffraction experiments, which were made in the range 1.5 5 K, showed that magnetic Bragg reflections in Er2Ni2Pb can be indexed by several propagation vectors that coexist over an extensive temperature range. Rather than a homogeneous magnetic structure that is simultaneously described by all the existing propagation vectors, several spatially separated structures appear to exist in Er2Ni2Pb. The appearance disappearance of representative reflections at TN 3.5 K, Tm1 3.0 K, Tm2 2.3 K, and Tm3 1.8 K denote magnetic phase transitions. The only magnetic state that is determined by a single propagation vector exists just below TN. In all other magnetic states, more than one propagation vectors are stable. Except for the lowest temperature state, which is commensurate, all other propagation vectors are incommensurate with respect to the crystal structure. Although the coexistence of several spatially separated magnetic structures can be explained by the competition of magnetic interactions along particular crystallographic directions, some of the details, e.g., the exact ground state magnetic structure, are still unclear and need further stud