Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin Films of BiFe_0.5Mn_0.5O₃

Abstract

Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.

Magnetic, electronic, and optical properties of double perovskite Bi2FeMnO6

“…This difference originates from the sign difference in the spin magnetic moments of Fe and Mn atoms. Although our theoretical calculations qualitatively show the XMCD signal characteristics of the pure BFMO sample, the experimental XMCD spectra show wiggles in L 2 /L 3 edges, cancelling the net magnetic moment possibly due to mixed-valence 7 states of Fe or Mn ions or site mixing between Fe or Mn ions. 33 With the XMCD sum rules, the details of which are given in the supplementary material, we find that the spin and orbital moments of Fe and Mn are consistent with those obtained directly from the self-consistent calculations using the spin-dependent GGA functional.…”

“…We also would like to point out that the magnitude of the total magnetic moment in the ferromagnetic state is between 7 and 8 µ B /f.u., which is too large when compared with the experimental measurement. 7 Furthermore, our electronic structure calculations (see below) identify BFMO to be semi-metallic for U = 0 eV, while an insulator with a band gap for U = 6.0 eV on both Fe and Mn sites. Therefore, both analyses of the magnetic instability and the electronic structure suggest that the on-site Coulomb interaction on the Fe and Mn 3d-electrons is crucial in addressing the properties of the tetragonal BFMO.…”

“…It is an extremely sensitive tool to experimentally identify any existing ferrimagnetic order in bulk solids down to the order of 0.001 µ B . There exists a simple set of sum rules 7,31,32 associated with the XMCD spectra, which can be very easily applied to obtain spin and orbital magnetic moments. For example, when the right circular and left circular x-ray absorption spectra for L 2 and L 3 edges are experimentally measured and denoted as µ Fig.…”

“…1,2 Physically, as pointed out by Aizu 3 and later on by other authors, 4,5 the ME coupling between magnetism and ferroelectricity is governed by a simultaneous breaking of inversion and time-reversal symmetries. Since its first prediction, 3 the search for multiferroic materials 6,7 has become one of the most active research areas in condensed matter and material physics. In particular, the ongoing search for room-temperature multiferroic systems has never been felt more essential.…”

Interface‐Coupled BiFeO3/BiMnO3 Superlattices with Magnetic Transition Temperature up to 410 K

“…[11][12][13][14][15] On the other hand, disordered double perovskites (notably BiFe 0.5 Mn 0.5 O 3 (BFMO) and Bi 2 CoMnO 6 (BCMO)) show a strongly enhanced T C albeit with lower magnetic moment than expected for the ordered structure. [ 16,17 ] Pálová et al extended the idea of ordered double perovskites by theoretically studying BFMO with an ordered nanoscale checkerboard structure (NCB-BFO/BMO, see Figure 1 a), i.e., columnar B -site ordering. [ 10 ] Their calculations predict that an ordered NCB-BFO/BMO would be ferroelectric and ferrimagnetic (FiM) with M S of 3.8 µ B /Fe-Mn pair and T C of 406 K, as a result of magnetic ordering arising from the superexchange coupling between the neighboring AFM-Fe and FM-Mn.…”