Electron transport and thermoelectric properties of layered perovskite LaBaCo2O5.5

We have investigated the systematic transport properties of the layered 112-type cobaltite LaBaCo2O5.5 by means of electrical resistivity, magnetoresistance, electroresistance and thermoelectric measurements in various conditions. In order to understand the complex conduction mechanism of LaBaCo2O5.5, the transport data have been analyzed using different theoretical models. The system shows semiconductor-semiconductor like transition (TSC) around 326K, corresponding to ferromagnetic transition and in the low temperature region resistivity data follows the Motts variable range hopping model. Interestingly, near and below the room temperature this compound depicts significant change in electro- and magnetoresistance behavior, the latter one is noteworthy near the magnetic phase boundary. The temperature dependence of thermopower, S(T), exhibits p-type polaronic conductivity in the temperature range of 60-320K and reaches a maximum value of 303 uV/K (at 120K). In the low temperature AFM region, the unusual S(T) behavior, generally observed for the cobaltite series LnBaCo2O5.5 (Ln = Rare Earth), is explained by the electron magnon scattering mechanism as previously described for perovskite manganites.Comment: 18 pages including fig

Spin-locking effect in the nanoscale ordered perovskite cobaltite LaBaCo2O6

A new nanoscale ordered perovskite cobaltite, which consists of 90 degree ordered domains of the layered-112 LaBaCo2O6 has been evidenced by high resolution- transmission electron microscopy. This new form, like the disordered La0.5Ba0.5CoO3 and ordered LaBaCo2O6, exhibits a ferromagnetic transition at TC around 179 K. However, it differs from the two previous forms by its strong magnetic anisotropy, and correlatively by its high value of coercivity (0.42 Tesla) at low temperature. We suggest that this behaviour originates from the locking of magnetic spins in the 90 degree oriented nano-domain. Moreover, one observes a semi-metal/semi-metal transition at TC with a maximum magnetoresistance of 6.5 % at this temperature.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

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