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

Abstract

Magnetic frustration and disorder are key ingredients to prevent the onset of magnetic order. In the disordered hexagonal double perovskite BaTi 1/2 Mn 1/2 O3, Mn 4+ cations, with S = 3/2 spins, can either form highly correlated states of magnetic trimers or dimers or remain as weakly interacting orphan spins. At low temperature (T ), the dimer response is negligible, and magnetism is dominated by the trimers and orphans. To explore the role of magnetic frustration, disorder and possibly of quantum fluctuations, the low-T magnetic properties of the remaining magnetic degrees of freedom of BaTi 1/2 Mn 1/2 O3 are investigated. Heat-capacity data and magnetic susceptibility display no evidence for a phase transition to a magnetically ordered phase but indicate the formation of a correlated spin state. The low-temperature spin dynamics of this state is then explored by µSR experiments. The zero field µ + relaxation rate data show no static magnetism down to T = 19 mK and longitudinal field experiments support as well that dynamic magnetism persists at low T . Our results are interpreted in terms of a spin glass state which stems from a disordered lattice of orphans spins and trimers. A spin liquid state in BaTi 1/2 Mn 1/2 O3, however, is not excluded and is also discussed.

Development of short and long-range magnetic order in the double perovskite based frustrated triangular lattice antiferromagnet Ba$$_{2}$$MnTeO$$_{6}$$

“…In such classical spin systems strong thermal fluctuations lead to magnetically ordered ground state via “order by disorder” mechanism 25 . The physics of frustrated triangular lattice is rich and diverse 1 , 26 , 27 , however, in many cases anti-site disorder, anisotropy and inter-plane interactions put a strong constraint on the ground-state spin dynamics and challenge theoretical paradigms 28 – 31 . The current challenge is to explore disorder-free frustrated triangular lattice antiferromagnets with exactly solvable ground state with potential to host exotic magnetism and spin dynamics.…”

A semi-empirical analysis of the paramagnetic susceptibility of solid state magnetic clusters

“…The mixed dimer/trimer material BaTi 0.5 Mn 0.5 O 3 remain characterized as a strongly frustrated magnet with relatively large intercluster interactions. As already observed [19], the system disorder is large, which may hinder the appearance of a quantum spin liquid, although the physics will be that of a correlated disordered quantum magnet. Thus, further investigations at low T are invited.…”

“…We now turn to the challenging case offered by the BaTi 0.5 Mn 0.5 O 3 [18,19] material, which presents spin dimers, trimers, and orphans. Its crystal structure is depicted in Figure 1(i).…”

“…The proposed model to χ assumes the following form: χ(T ) = q trim χ trim + q dim χ dim + q orp χ orp + χ 0 (10) where q orp is the molar fraction of the orphan spins in the sample and χ orp is the orphan spin susceptibility. As discussed elsewhere [18,19], the fractions are statistically determined to be: q trim = q orp = 1/16, and q dim = 2/16. We adopt a Curie-Weiss form to χ orp (with C orp and θ orp parameters).…”

Signature of a randomness-driven spin-liquid state in a frustrated magnet

“…In Fig. 4 (a), we present ZF-µSR spectra at a few representative temperatures that muon asymmetry remains more or less unchanged for all temperatures, which proves the absence of a phase transition down to 1.55 K [47]. The time dependence of the muon asymmetry provides the information concerning internal field distributions at the muon interstitial stopping site.…”