Associated Lam\'{E} Equation, Periodic Potentials and sl(2,R)

We propose a new approach based on the algebraization of the Associated Lam\'{e} equation $$-\psi''(x) + [ m(m+1)k^{2}sn^{2}x + \ell(\ell+1)k^{2}(cn^{2}x/dn^{2}x)]\psi(x) = E\psi(x)$$ within sl(2,R) to derive the corresponding periodic potentials. The band edge eigenfunctions and energy spectra are explicitly obtained for integers m,$\ell$. We also obtain the explicit expressions of the solutions for half-integer m and integer or half-integer $\ell$.Comment: 8 pages, no figure, tex file(version 2.09

Biferroic YCrO3

YCrO3 which has a monoclinic structure, shows weak ferromagnetism below 140 K (TN) and a ferroelectric transition at 473 K accompanied by hysteresis. We have determined the structure and energetics of YCrO3 with ferromagnetic and antiferromagnetic ordering by means of first-principles density functional theory calculations, based on pseudopotentials and a plane wave basis. The non-centrosymmetric monoclinic structure is found to be lower in energy than the orthorhombic structure, supporting the biferroic nature of YCrO3.Comment: 16 pages including figure

Nonequilibrium magnetic properties of single-crystalline La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>CoO<SUB>3</SUB>

Magnetic and electric properties of a single crystal of La0.7Ca0.3CoO3 have been experimentally studied. The system attains a ferromagnetic spontaneous moment below 170 K and exhibits a reentrant spin-glass phase below 100 K. In the ordered and the reentrant phases, the low-field magnetic properties are strongly direction dependent, showing considerably higher magnetization values perpendicular than parallel to the c axis. Magnetic relaxation experiments show that both the ferromagnetic and the reentrant spin-glass phases are nonequilibrium states, where the system exhibits magnetic aging characteristic of spin glasses and disordered and frustrated ferromagnets

Incoherent Effect of Fe and Ni Substitutions in the Ferromagnetic-Insulator La0.6Bi0.4MnO3+d

A comparative study of the effect of Fe and Ni doping on the bismuth based perovskite La0.6Bi0.4MnO3.1, a projected spintronics magnetic semiconductor has been carried out. The doped systems show an expressive change in magnetic ordering temperature. However, the shifts in ferromagnetic transition (TC) of these doped phases are in opposite direction with respect to the parent phase TC of 115 K. The Ni-doped phase shows an increase in TC ~200 K, whereas the Fe-doped phase exhibits a downward shift to TC~95 K. Moreover, the Fe-doped is hard-type whereas the Ni-doped compound is soft-type ferromagnet. It is observed that the materials are semiconducting in the ferromagnetic phase with activation energies of 77 & 82 meV for Fe & Ni-doped phases respectively. In the presence of external magnetic field of 7 Tesla, they exhibit minor changes in the resistivity behaviours and the maximum isothermal magnetoresistance is around -20 % at 125 K for the Ni-phase. The results are explained on the basis of electronic phase separation and competing ferromagnetic and antiferromagnetic interactions between the various mixed valence cations.Comment: 18 pages including figure

Ferromagnetism and magneto-dielectric effect in insulating LaBiMn4/3Co2/3O6 thin films

High quality epitaxial thin films of LaBiMn4/3Co2/3O6 perovskite were fabricated on (001)-oriented SrTiO3 and LaAlO3 substrates by the pulsed laser deposition technique. Magnetization measurements reveal a strong magnetic anisotropy and a ferromagnetic behavior that is in agreement with a super-exchange interaction between Mn4+ and Co2+ ions, which are randomly distributed in the B-site. A distinct anomaly is observed in the dielectric measurements at 130K corresponding to the onset of the magnetic ordering, suggesting a coupling. Above this temperature, the extrinsic Maxwell-Wagner effect is dominating. Theses results are explained using the Raman spectroscopic studies indicating a weak spin-lattice interaction around this magnetic transition.Comment: Submitted to Appl. Phys. Lett. (2008