Magnetic order in four-layered Aurivillus phases

Abstract

We determine the viability of 4-layered Aurivillius phases to exhibit long-range magnetic order above room temperature. We use Monte Carlo simulations to calculate transition temperatures for an effective Heisenberg model containing a minimal set of required couplings. The magnitude of the corresponding coupling constants has been determined previously from electronic structure calculations for Bi5FeTi3O15, for which we obtain a transition temperature far below room temperature. We analyze the role of further neighbor interactions within our Heisenberg model, in particular that of the second-nearest-neighbor coupling within the perovskite-like layers of the Aurivillius structure, as well as that of the weak inter-layer coupling, in order to identify the main bottleneck for achieving higher magnetic transition temperatures. Based on our findings, we show that the most promising strategy to obtain magnetic order at higher temperatures is to increase the concentration of magnetic cations within the perovskite-like layers, and we propose candidate compounds where magnetic order could be achieved above room temperature.

Novel Aurivillius Bi4Ti3−2xNbxFexO12 phases with increasing magnetic-cation fraction until percolation: a novel approach for room temperature multiferroism

“…The magnetic order in Aurivillius oxides is known to require a threshold fraction of magnetic species at the B-site. 29 This is related to the short-range character of the superexchange interactions, and the necessity of having percolation of magnetic species at the B-cation sublattice, i.e. that each magnetic species had at least one magnetic nearest neighbor.…”

“…24,25 Multiferroism in these materials was devised by the incorporation of magnetically active BiMO 3 layers, where M is Fe 3+ , Co 3+ 18 thin films with n(m) = 1(4) and 2 (5), respectively. 27,28 The magnetic order requires a threshold fraction of magnetic species at the B-site, 29 and then high n, and so m values are targeted. However, high-m Aurivillius phases are difficult to prepare and have a tendency to form intergrowths of compounds with alternating m values.…”

Progress and Perspectives on Aurivillius-Type Layered Ferroelectric Oxides in Binary Bi4Ti3O12-BiFeO3 System for Multifunctional Applications

“…With a low concentration of magnetic cations, there is a strong AFM coupling between Fe 3+ cations in nearest-neighbor positions, whereas the coupling between further neighbors is rather weak. When it has a higher concentration, the FM properties are mainly from the presence of a small inhomogeneous magnetic Fe ion distribution in a nano-region, leading to a short-range magnetic order (FM behavior) [105]. It was also proved that when the BFTO-n have higher integer or fractional n values, the Fe/Ti ions is inhomogeneously distributed in octahedral positions of the perovskite blocks and structural inhomogeneity easily exists in these layered structure, which lead to strong effects on the magnetic properties [106].…”

Polarization rotation in Bi4Ti3O12 by isovalent doping at the fluorite sublattice

“…Isovalent doping has also been explored in experiments, but is limited to PL sites [30,31]. We note that developing ferroelectric functionalities by doping with transition metals has been explored by first principles methods but, consistent with experimental work to date, only the Ti site in the PL layer was investigated [32,33].…”