arXiv subjects

D. Kasinathan

Publications and source records attributed to D. Kasinathan.

22 records · Page 2Linked to original sources

arXiv2008

Effect of pressure on the magnetostructural transition in SrFe2As2

We present a systematic pressure study of poly- and single crystalline SrFe2As2 by electrical resistivity and X-ray diffraction measurements. SrFe2As2 exhibits a structural phase transition from a tetragonal to an orthorhombic phase at T0=205 K. The structural phase transition is intimately linked to a spin-density-wave transition taking place at the same temperature. Our pressure experiments show that T0 shifts to lower temperatures with increasing pressure. We can estimate a critical pressure of 4 to 5 GPa for the suppression of T0 to zero temperature. At pressures above 2.5 GPa the resistivity decreases significantly below Tx=40 K hinting at the emergence of superconductivity but no zero-resistance state is observed up to 3 GPa.

cond-mat.supr-con↗

arXiv2008

Possible re-entrant superconductivity in EuFe2As2 under pressure

We studied the temperature-pressure phase diagram of EuFe2As2 by measurements of the electrical resistivity. The antiferromagnetic spin-density-wave transition at T_0 associated with the FeAs-layers is continuously suppressed with increasing pressure, while the antiferromagnetic ordering temperature of the Eu 2+ moments seems to be nearly pressure independent up to 2.6 GPa. Above 2 GPa a sharp drop of the resistivity, ρ(T), indicates the onset of superconductivity at T_c \approx 29.5 K. Surprisingly, on further reducing the temperature ρ(T) is increasing again and exhibiting a maximum caused by the ordering of the Eu 2+ moments, a behavior which is reminiscent of re-entrant superconductivity as it is observed in the ternary Chevrel phases or in the rare-earth nickel borocarbides.

cond-mat.supr-con↗

arXiv2008

Strong coupling between magnetic and structural order parameters in SrFe2As2

X-ray and Neutron diffraction as well as muon spin relaxation and Mössbauer experiments performed on SrFe$_2$As$_2$ polycrystalls confirm a sharp first order transition at $T_0 = 205$,K corresponding to an orthorhombic phase distortion and to a columnar antiferromagnetic Fe ordering with a propagation vector (1,0,1), and a larger distortion and larger size of the ordered moment than reported for BaFe$_2$As$_2$. The structural and the magnetic order parameters present an remarkable similarity in their temperature dependence from $T_0$ down to low temperatures, showing that both phenomena are intimately connected. Accordingly, the size of the ordered Fe moments scale with the lattice distortion when going from SrFe$_2$As$_2$ to BaFe$_2$As$_2$. Full-potential band structure calculations confirm that the columnar magnetic order and the orthorhombic lattice distortion are intrinsically tied to each other.

cond-mat.supr-con↗

arXiv2006

Optical Properties and Magnetic Field-Induced Phase Transitions in the Ferroelectric State of Ni$_3$V$_2$O$_8$

We use a combination of optical spectra, first principles calculations, and energy dependent magneto-optical measurements to elucidate the electronic structure and to study the phase diagram of Ni$_3$V$_2$O$_8$. We find a remarkable interplay of magnetic field and optical properties that reveals additional high magnetic field phases and an unexpected electronic structure which we associate with the strong magneto-dielectric couplings in this material over a wide energy range. Specifically, we observed several prominent magneto-dielectric effects that derive from changes in crystal field environment around Ni spine and cross-tie centers. This effect is consistent with a field-induced modification of local structure. Symmetry-breaking effects are also evident with temperature. We find Ni$_3$V$_2$O$_8$ to be an intermediate gap, local moment band insulator. This electronic structure is particularly favorable for magneto-dielectric couplings, because the material is not subject to the spin charge separation characteristic of strongly correlated large gap Mott insulators, while at the same time remaining a magnetic insulator independent of the particular spin order and temperature.

cond-mat.str-el↗