Yuri V. Sushko

Hydrostatic pressure effects on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: evidence for pressure-enhanced antiferromagnetic instability

Abstract Hydrostatic pressure effects on the temperature- and magnetic field dependencies of the in-plane and out-of-plane magnetization of the bi-layered perovskite Sr 3 Ru 2 O 7 have been studied by SQUID magnetometer measurements under a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature value of the paramagnetic susceptibility has been found to systematically decrease with increasing pressure. The effect is accompanied by an increase of the temperature T max of a pronounced peak of susceptibility. Thus, magnetization measurements under hydrostatic pressure reveal that the lattice contraction in the structure of Sr 3 Ru 2 O 7 promotes antiferromagnetism and not ferromagnetism. The effects can be explained by the enhancement of the inter-bi-layer antiferromagnetic spin coupling, driven by the shortening of the superexchange path, and suppression, due to the band-broadening effect, of competing itinerant ferromagnetic correlations.

Temperature and field dependence of the energy gap of MgB 2 / Pb planar junctions

We have constructed MgB 2 /Pb planar junctions for both temperature and field dependence studies. Our results show that the small gap is a true bulk property of MgB 2 superconductor, not due to surface effects. The temperature dependence of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect of magnetic field on junctions suggests that the energy gap of MgB 2 depends nonlinearly on the magnetic field. Moreover, MgB 2 has an upper critical field of 15 T, in agreement with some reported H c 2 from transport measurements.

Novel Magnetism of EDO-TTFX2 Salts (X=Br, I)

Charge transfer complexes of EDO-TTFX, (X=Br, I) form low-D structures featured with coordination-like-bond formation of X with counter anions, giving unconventional magnetic conductive systems with magnetic anions. (EDO-TTFI 2 ) 2 M(nmt) 2 (M=Pt. Ni) are 1D conductors interacting with ferromagnetic ID M(mnt) 2 chains. Applying pressure gives a unique ferromagnetic domain formation. 2D (EDO-TTFBr 2 ) 2 FeBr 4 is metallic, where ID FeBr 4 chains take an antiferromagnetic transition at a very high T N (=13.5K) with a short-range-order effect around the resistivity minimum (30K), suggesting the presence of strong π-d interaction.

Pressure Dependence of Magnetic and Superconducting Transitions in Sodium Cobalt Oxides NaxCoO2

The results of dc magnetization measurements under hydrostatic (heliumgas) pressure are presented for an ambient pressure superconductor Na0.35CoO21.4D2O and its precursor compound Na0.75CoO2 known to combine metallic conductivity with an unusual magnetic state below ∼22K.The results of dc magnetization measurements under hydrostatic (heliumgas) pressure are presented for an ambient pressure superconductor Na{sub 0.35}CoO{sub 2}1.4D{sub 2}O and its precursor compound Na{sub 0.75}CoO{sub 2} known to combine metallic conductivity with an unusual magnetic state below {approx}22K.

Unconventional Properties of TTF-Based Organic Magnetic Conductors

Unconventional magnetic properties of various TTF-based π-d interaction systems are presented. (D)2FeBr4 (D=DMET, EDTDM) are quasi-2D metals consisting of alternating stacking of donor π-electron conducting sheets and square lattice d-spins of FeBr4 - anion sheets. The magnetoresistance is strongly affected by changes of Fe3+ spin arrangement in the ordered state. Especially, for (EDTDM)2FeBr4, a large negative magnetoresistance appears in the vicinity of an MI transition. In (EDO-TTFBr2)2FeX4 (X=C1, Br) having similar sandwich structure to (D)2FeBr4, the presence of the Br atom of the donor bonded semicovalently to X atom of FeX4 - gives strong π-d interaction, which produces a strong correlation between the electron transport and magnetism in addition to a high Neel temperature with a complicated spin structure. (EDO- TTFI2)M(mnt)2 (M=Ni, Pt) are featured by a combination of 1D metal of EDO-TTFI2 columns and 1D ferromagnetic chain of M(mnt)2. For M=Pt, weak AF inter-chain interaction brings about a metamagnetic feature. The application of pressure enhances ferromagnetic features with an anomalous hysteretic hump.

Temperature and field dependence of the energy gap of MgB2/Pb planar junctions

We have constructed MgB 2 /Pb planar junctions for both temperature and field dependence studies. Our results show that the small gap is a true bulk property of MgB 2 superconductor, not due to surface effects. The temperature dependence of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect of magnetic field on junctions suggests that the energy gap of MgB 2 depends nonlinearly on the magnetic field. Moreover, MgB 2 has an upper critical field of 15 T, in agreement with some reported H c 2 from transport measurements.

Temperature and field dependence of the energy gap ofMgB2/Pbplanar junctions

We have constructed MgB 2 /Pb planar junctions for both temperature and field dependence studies. Our results show that the small gap is a true bulk property of MgB 2 superconductor, not due to surface effects. The temperature dependence of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect of magnetic field on junctions suggests that the energy gap of MgB 2 depends nonlinearly on the magnetic field. Moreover, MgB 2 has an upper critical field of 15 T, in agreement with some reported H c 2 from transport measurements.