Magnetic and transport properties of the spin-state disordered oxide La0.8Sr0.2Co_{1-x}Rh_xO_{3-δ}

Abstract

We report measurements and analysis of magnetization, resistivity and thermopower of polycrystalline samples of the perovskite-type Co/Rh oxide La${}_{0.8}$Sr${}_{0.2}$Co${}_{1-x}$Rh${}_x$O${}_{3-\delta }$. This system constitutes a solid solution for a full range of $x$,in which the crystal structure changes from rhombohedral to orthorhombic symmetry with increasing Rh content $x$. The magnetization data reveal that the magnetic ground state immediately changes upon Rh substitution from ferromagnetic to paramagnetic with increasing $x$ near 0.25, which is close to the structural phase boundary. We find that one substituted Rh ion diminishes the saturation moment by 9 ${\mu }_B$, which implies that one Rh${}^{3+}$ ion makes a few magnetic Co${}^{3+}$ ions nonmagnetic (the low spin state), and causes disorder in the spin state and the highest occupied orbital. In this disordered composition ($0.05\le x\le 0.75$), we find that the thermopower is anomalously enhanced below 50 K. In particular, the thermopower of $x$=0.5 is larger by a factor of 10 than those of $x$=0 and 1, and the temperature coefficient reaches 4 $\mu$V/K${}^2$ which is as large as that of heavy-fermion materials such as CeRu${}_2$Si${}_2$.

8 pages, 6 figures, accepted to Phys. Rev. B

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• Weak Ferromagnetism in LaCo1-xRhxO3: Anomalous Magnetism Emerging between Two Nonmagnetic End Phases
• Ga${}^{3+}$-substitution effects in the weak ferromagnetic oxide LaCo${}_{0.8}$Rh${}_{0.2}$O${}_3$
• Thermoelectric transport in the layered Ca${}_3$Co${}_{4-x}$Rh${}_x$O${}_9$ single crystals
• Spin state of Co${}^{3+}$ in LaCo${}_{1-x}$Rh${}_x$O${}_3$ investigated by structural phenomena
• Cluster Spin Glass State in Ba${}_3$Sb${}_{1+x}$Co${}_{2-x}$O${}_{9-\delta }$: Cation Disorder and Mixed-Valence Co Dimers