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

Abstract

We report a structural/magnetic investigation by X-ray absorption spectroscopy (XAS), neutron diffraction, dc-susceptibility (χ dc ) and electron spin resonance (ESR) of the 12R-type perovskite BaTi 1/2 Mn 1/2 O3. 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 ≤ T ≤ 1000 K. A scenario is presented under which the magnetism is explained by considering magnetic dimers and trimers, with exchange constants Ja/kB = 200(2) K and J b /kB = 130(10) K, and orphan spins. Thus, BaTi 1/2 Mn 1/2 O3 is proposed as a rare case of an intrinsically disordered S = 3/2 spin gap system with a frustrated ground state.

Dynamic magnetism in the disordered hexagonal double perovskite BaTi1/2Mn1/2O3

“…All analysis so far [23,29,30] and our results [31] support that the M (2) site is equally occupied by either Mn or Ti atoms. Therefore, the relative fraction of dimers, trimers and orphans are statistically determined as in Ref.…”

“…The BaTi 1/2 Mn 1/2 O 3 structure is presented in Fig. 1(a) [23,29,30] (see Ref. [31] for further support from new resonant diffraction experiments).…”

“…High quality polycrystalline samples were synthesized by the solid state reaction method as in Ref. [23]. Synchrotron X-ray diffraction experiments were carried out at the XRD1 beamline of the LNLS-CNPEM, Brazil [24].…”

“…The coupling of magnetic dimers and trimers are described by two strong exchange constants J 1 and J 2 ( Fig. 1(b)), which were shown to be of comparable size [23]. As a function of T , the dimer contribution to magnetism is exponentially suppressed and we can safely assume that at low-T the remaining magnetic degrees of freedom are due to orphan spins and magnetic trimers.…”

“…Therefore, the relative fraction of dimers, trimers and orphans are statistically determined as in Ref. [23]. It results that 1/8 of the Mn are orphans, half pair up to form dimers and 3/8 form trimers.…”