Yohei Kashiwada

Magnetic, electrical and thermal properties of La0.80Sr0.20(MnyCo1−y)O3

Abstract The thermal conductivity κ, thermoelectric power S, electrical resistivity ρ and magnetization M of La0.80Sr0.20 (MnyCo1−y)O3 has been measured. By Mn substitution for Co, the initial ferromagnetic-metal behavior is promptly suppressed and ρ(T) becomes semiconductive. In the semiconductive composition range, S is remarkably enhanced and κ is reduced. As a result, pretty large values of the thermoelectric figure of merit Z are realized.

Thermal conductivity of Pr0.65(Ca1−ZSrZ)0.35MnO3 under applied field

Abstract The thermal conductivity κ ( T ) of Pr 0.65 (Ca 1− Z Sr Z ) 0.35 MnO 3 (0⩽ Z ⩽1.0) has been measured under the applied field of up to 5 T . For Z =0.3 and 0.4, where the ferromagnetic metal (FM-M) state is competitive with the charge/orbital ordered (CO/OO) state, κ ( T ) is enhanced and shows the hysteresis below the FM-M transition temperature T c . The hysteresis of κ ( T ) is wiped out and T c increases rapidly with the increase of the applied fields. These κ ( T ) behaviors originate from the stabilization of the FM-M state due to the rapid suppression of the CO/OO state.

Thermal Conductivity Anomalies of RECoO3 (RE = La-Nd) Related to Valency and Spin State of Co Ion

The thermal conductivities κ( T ) of Co- and La-site-substituted LaCoO 3 were measured and the origin of the κ( T ) peak was investigated. The sharp κ( T ) peak at approximately 30 K is strongly suppressed by the introduction of a small amount of Jahn–Teller (JT)-active Co 4+ ions because of Co-site substitution by divalent ions such as Ni 2+ and Cu 2+ , similarly to the La-site substitution by Sr 2+ . In contrast, the κ( T ) peak of samples with the Co-site substituted by tetravalent ions such as Sn 4+ and Zr 4+ , which introduce Co 2+ ions, moderately decreased. The temperature at which a small and broad κ( T ) peak in the Pr-containing RECoO 3 [rare-earth (RE) = La 1- y Pr y and Pr 1- z Nd z ] is also observable shifts from 110 K for RE = La 0.5 Pr 0.5 to 180 K for RE = Pr and Pr 0.5 Nd 0.5 , which corresponds to the spin-state transition temperature of Co 3+ ions.

Enhanced thermoelectric properties at x/spl sim/0.1 in La/sub 1-x/Sr/sub x/CoO/sub 3/ and La/sub 1-x/Sr/sub x/(Co/sub 1-y/M/sub y/)O/sub 3/ (M=Cr, Cu)

The thermoelectric properties of the La/sub 1-x/Sr/sub x/CoO/sub 3/ system have been investigated from 10 K to 300 K. The figure of merit Z and power factor P increase with increasing Sr concentration x and show a maximum for x=0.10-0.15, where the ferromagnetic (FM) order starts to appear. The maximum Z value (Z= 150 x 10/sup -6/ K/sup -1/ at 230 K for x=0.10) is larger than those of layered cobaltites. The Z and P values are enhanced by the 5 % Co-site substitution by Cr for the overdoped concentration (x=0.20), but are depressed for the nearly optimum doped one (x=0.15). The results are discussed in conjunction with the carrier density n of this system.