Magnetic dimers and trimers in the disordered $S=3/2$ spin system BaTi${}_{1/2}$Mn${}_{1/2}$O${}_3$

Abstract

We report a structural/magnetic investigation by X-ray absorption spectroscopy (XAS), neutron diffraction, dc-susceptibility ($χ_{\mbox{dc}}$) and electron spin resonance (ESR) of the 12R-type perovskite BaTi${}_{1/2}$Mn${}_{1/2}$O${}_3$. Our structural analysis by neutron diffraction supports the existence of structural trimers with chemically disordered occupancy of Mn${}^{4+}$ and Ti${}^{4+}$ ions, with the valence of the Mn ions confirmed by the XAS measurements. The magnetic properties are explored by combining dc-susceptibility and $X$-band ($9.4$ GHz) electron spin resonance, both in the temperature interval of $2\le T\le 1000$ K. A scenario is presented under which the magnetism is explained by considering magnetic dimers and trimers, with exchange constants $J_a/k_B=200(2)$ K and $J_b/k_B=130(10)$ K, and orphan spins. Thus, BaTi${}_{1/2}$Mn${}_{1/2}$O${}_3$ is proposed as a rare case of an intrinsically disordered $S=3/2$ spin gap system with a frustrated ground state.

8 pages, 7 figures, final version to appear in Phys Rev B