Strain-tuned enhancement of ferromagnetic TC to 176 K in Sm-doped BiMnO3 thin films and determination of magnetic phase diagram

Abstract

BiMnO3 is a promising multiferroic material but it’s ferromagnetic TC is well below room temperature and the magnetic phase diagram is unknown. In this work, the relationship between magnetic transition temperature (TC) and the substrate induced (pseudo-) tetragonal distortion (ratio of out-of-plane to in-plane lattice parameters, c/a) in BiMnO3 thin films, lightly doped to optimize lattice dimensions, was determined. For c/a > 0.99, hidden antiferromagnetism was revealed and the magnetisation versus temperature curves showed a tail behaviour, whereas for c/a < 0.99 clear ferromagnetism was observed. A peak TC of up to 176 K, more than 70 K higher than for bulk BiMnO3, was achieved through precise strain tuning. The TC was maximised for strong tensile in-plane strain which produced weak octahedral rotations in the out-of-plane direction, an orthorhombic-like structure, and strong ferromagnetic coupling.

High-throughput computational discovery of In2Mn2O7 as a high Curie temperature ferromagnetic semiconductor for spintronics

“…While In 2 Mn 2 O 7 does not yet fulfill the requirement of room-temperature ferromagnetism, its Curie temperature could be potentially increased with epitaxial strain. [66][67][68] Indeed, as shown in Supplementary Information, we find that tensile stress due to the lattice mismatch to some semiconductor substrates (such as Si and GaAs) can effectively increase the Curie temperature of In 2 Mn 2 O 7 , but it needs to be practiced with caution as it has adverse effects on the effective mass (see Fig. S3).…”

“…Δμ O2 indicates the oxygen chemical potential (referred to the isolated molecule) below which the compound is stable in an oxidising atmosphere. Oxidisation is more likely for compounds with a more negative Δμ O2 Curie temperature as it has been demonstrated for EuO and BiMnO 3 [68][69][70][71][72].…”

Creating Ferromagnetic Insulating La0.9Ba0.1MnO3 Thin Films by Tuning Lateral Coherence Length

“…It can also be termed a vertical coherence length. In this low-thickness regime, in addition to modification of degrees of freedom from substrate interactions, strain-relieving defects from substrate–film lattice mismatch also come into play, which complicate the understanding of low-dimensional effects. − …”

Strain Engineering of Epitaxial Oxide Heterostructures Beyond Substrate Limitations

“…Strong coupling and complex interplay between strain and spin, charge, orbital and lattice degrees of freedom provide a fertile new ground for creating exotic phases and realizing novel functionalities in complex oxide thin films and heterostructures [1][2][3][4][5][6][7][8] . This has enabled epitaxial strain as a powerful tool for the creation of new ground states (associated with phase transitions) [9][10][11][12][13] , the improvement of catalytic activity [14][15][16] , and the manipulation of electric and magnetic properties [17][18][19][20][21][22][23][24] including greatly enhanced superconducting, 26,27 ferroelectric 28,29 and ferromagnetic 31,32 transition temperatures. To realize these emergent phenomena, the availability of appropriate single-crystal substrates for the growth of high-quality epitaxial oxide films with a desired strain state cannot be overemphasized 4,33 .…”