Field-induced first-order magnetic phase transition in an intermetallic compound, Nd7Rh3: Evidence for kinetic-hindrance, phase co-existence and percolative conduction

The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, was previously known to exhibit two magnetic transitions, one at 32 K and the other at 10 K (in zero magnetic field). Here, we report the existence of a field-induced first-order antiferromagnetic to ferromagnetic transition at 1.8 K in this compound. On the basis of the measurements of isothermal magnetization and magnetoresistance, we provide evidence for the occurence of kinetic-hindrance, proposed in the literature, resulting in phase co-existence (super-cooled ferromagnetic + antifferomagnetic) and percolative electrical conduction in this stoichiometric intermetallic compound. A point of emphasis, as inferred from ac susceptibility data, is that such a co-existing phase is different from spin-glasses, thereby clarifying a question raised in the field of phase-separation.Comment: A Shortened version will appear in print in PRB (Rapid Comm). Phys. Rev. B (Rapid Comm), in pres

The Semiclassical Limit for SU(2)SU(2) and SO(3)SO(3) Gauge Theory on the Torus

We prove that for $SU(2)$ and $SO(3)$ quantum gauge theory on a torus, holonomy expectation values with respect to the Yang-Mills measure d\mu_T(\o) =N_T^{-1}e^{-S_{YM}(\o)/T}[{\cal D}\o] converge, as $T\downarrow 0$, to integrals with respect to a symplectic volume measure $\mu_0$ on the moduli space of flat connections on the bundle. These moduli spaces and the symplectic structures are described explicitly.Comment: 18 page

An anomalous magnetic phase transition at 10 K in Nd7Rh3

The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has been shown recently by us to exhibit a signature of magnetic phase-coexistence phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric intermetallic compounds, bearing a relevance to the trends in the field of electronic phase-separation. In order to characterize this compound further, we have carried out dc magnetic susceptibility (chi), electrical resistivity, magnetoresistance and heat-capacity measurements as a function temperature (T= 1.8 to 300 K). The results reveal that this compound exhibits another unusual finding at the 10K-transition in the sense that the plot of chi(T) shows a sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve shows a downturn below the transition. In addition, the sign of magnetoresistance is negative and the magnitude is large over a wide temperature range in the vicinity of magnetic ordering temperature, with a sharp variation at 10 K. The results indicate that the transition below 10 K is first-order in its character.Comment: Appeared in JPCM (Letters) 18 (2006) L40

Magnetic behaviour of quasi-one-dimensional oxides, Ca3_3Co(1+x)_(1+x)Mn1−x_{1-x}O6_6

The results of ac and dc magnetization and heat capacity measurements on the oxides, Ca$_3$Co$_{1+x}$Mn$_{1-x}$O$_6$, forming in a K$_4$CdCl$_6$-derived rhombohedral quasi-one-dimensional crystal structure, are reported. As far as Ca$_3$Co$_2$O$_6$ is concerned, the results reveal truly complex nature of the two magnetic transitions, identified to set in at 24 and 12 K in the previous literature. However, partial replacement of Co by Mn apparently results in a long magnetic ordering of an antiferromagnetic type (below 13 and 18 K for x= 0.0 and 0.25 respectively), instead of spin-glass freezing in spite of the fact that there is Co-Mn disorder; in addition, interestingly there are hysteretic spin reorientation effects as revealed by isothermal magnetization behavior

Large magnetoresistance in the magnetically ordered state as well as in the paramagnetic state near 300 K in an intermetallic compound,Gd7Rh3

We report the response of electrical resistivity $\rho$ to the application of magnetic fields (H) up to 140 kOe in the temperature interval 1.8-300 K for the compound, Gd7Rh3, ordering antiferromagnetically below 150 K. We find that there is an unusually large decrease of $\rho$ for moderate values of H in the close vicinity of room temperature uncharacteristic of paramagnets, with the magnitude of the magnetoresistance increasing with decreasing temperature as though the spin-order contribution to $\rho$ is temperature dependent. In addition, this compound exhibits giant magnetoresistance behaviour at rather high temperatures (above 77 K) in the magnetically ordered state due to a metamagnetic transition.Comment: Europhyics Letters, in pres

Modulus stabilization of generalized Randall Sundrum model with bulk scalar field

We study the stabilization of inter-brane spacing modulus of generalized warped brane models with a nonzero brane cosmological constant. Employing Goldberger-Wise stabilization prescription of brane world models with a bulk scalar field, we show that the stabilized value of the modulus generally depends on the value of the brane cosmological constant. Our result further reveals that the stabilized modulus value corresponding to a vanishingly small cosmological constant can only resolve the gauge hierarchy problem simultaneously. This in turn vindicates the original Randall-Sundrum model where the 3-brane cosmological constant was chosen to be zero.Comment: 12 Pages, 1 figure, Revtex, Version to appear in Euro. Phys. Let

Slowly Rotating Dilaton Black hole In Anti-de Sitter Spacetime

Rotating dilaton black hole solution for asymptotically anti-de Sitter spacetime are obtained in the small angular momentum limit with an appropriate combination of three Liouville-type dilaton potentials. The angular momentum, magnetic dipole moment and the gyromagnetic ratio of such a black hole are determined for arbitrary values of the dilaton-electromagnetic coupling parameter.Comment: 5 pages, Revtex, To appear in Phys.Rev.