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

TL;DR

This study investigates the magnetic and structural properties of BaTi$_{1/2}$Mn$_{1/2}$O$_{3}$, revealing disordered magnetic dimers and trimers in a frustrated $S=3/2$ spin system with a spin gap.

Contribution

It provides the first detailed analysis of magnetic dimers and trimers in a disordered $S=3/2$ system, combining multiple spectroscopic and diffraction techniques.

Findings

Structural trimers with disordered Mn/Ti occupancy confirmed.

Magnetic exchange constants for dimers and trimers determined.

Identifies BaTi$_{1/2}$Mn$_{1/2}$O$_{3}$ as a disordered spin gap system.

Abstract

We report a structural/magnetic investigation by X-ray absorption spectroscopy (XAS), neutron diffraction, dc-susceptibility ($\chi_{\mbox{dc}}$) 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 $2\leq T\leq1000$ 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.