Magnetic dimers and trimers in the disorderedS=32spin systemBaTi1/2Mn1/2O3

Abstract

We report a structural-magnetic investigation by x-ray absorption spectroscopy (XAS), neutron diffraction, dc susceptibility $({\ensuremath{\chi}}_{\text{dc}})$, and electron spin resonance (ESR) of the 12R-type perovskite ${\text{BaTi}}_{1/2}{\text{Mn}}_{1/2}{\text{O}}_{3}$. Our structural analysis by neutron diffraction supports the existence of structural trimers with chemically disordered occupancy of ${\text{Mn}}^{4+}$ and ${\text{Ti}}^{4+}$ 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 $2\ensuremath{\le}T\ensuremath{\le}1000$ K. A scenario is presented under which the magnetism is explained by considering magnetic dimers and trimers, with exchange constants ${J}_{a}/{k}_{B}=200\phantom{\rule{0.16em}{0ex}}(2)$ K and ${J}_{b}/{k}_{B}=130\phantom{\rule{0.16em}{0ex}}(10)$ K, and orphan spins. Thus, ${\text{BaTi}}_{1/2}{\text{Mn}}_{1/2}{\text{O}}_{3}$ is proposed as a rare case of an intrinsically disordered $S=\frac{3}{2}$ spin gap system with a frustrated ground state.