Large Thermal Conductivity due to Spins in the Two-Dimensional Spin System LaSrFeO4

We have measured the temperature dependences of the thermal conductivity of LaSrFe1-xGaxO4 (x = 0; 0:01) single crystals with a two-dimensional (2D) antiferromagnetic (AF) spin network of Fe3+ spins with the spin quantum number S = 5/2 in zero field and a magnetic field of 14 T. A peak originating from the thermal conductivity due to spins, kappa(spin), has been observed at similar to 110K in the temperature dependence of the thermal conductivity in the ab-plane parallel to the 2D AF spin network. The maximum value of kappa(spin) is similar to 12W/Km, which is comparable to that in La2CuO4 with a 2D AF spin system of S = 1/2. By comparison with the temperature dependence of kappa(spin) in La2CuO4, we have found that the peak temperature where kappa(spin) shows a peak tends to increase with increasing width of the magnetic energy band, namely, with increasing product of the superexchange interaction between the nearest neighbor spins and the spin quantum number, JS, in 2D AF spin systems. Moreover, it has been concluded that kappa(spin) is expected to be enhanced by reducing the amount of impurities and imperfections in a crystal with a 2D AF spin network with a large JS value.