TY - JOUR
T1 - Magnetoelastic coupling behaviour of nanocrystalline ε-Fe2O3
AU - Haines, C. R. S.
AU - Gich, M.
AU - García-Muñoz, J. L.
AU - Romaguera, A.
AU - Ma, Z.
AU - Costa, M. B.
AU - Carpenter, M. A.
N1 - Funding Information: This work was funded by grant no. RPG-2016-298 from the Leverhulme Trust. RUS facilities in Cambridge were established through grants from the Natural Environment Research Council (Grants No. NE/B505738/1 and No. NE/F017081/1) and the Engineering and Physical Sciences Research Council (Grant No. EP/I036079/1) to MAC. We also acknowledge financial support from the Spanish Ministry of Science, Innovation, and Universities (Grants No. RTI2018-098537-B-C21, cofunded by ERDF from EU, and FUNFUTURE (CEX2019-000917-S)) and funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 819623). ALBA synchrotron is also acknowledged. Support is acknowledged from the European Union Horizon 2020 Research and Innovation Programme under Marie Skłodowska-Curie grant 861046 (BIOREMIA) for MBC.
PY - 2023/10/1
Y1 - 2023/10/1
N2 - Preparation of a ceramic sample which preserved the nanoscale grain sizes of ∼10–30 nm has allowed elastic and anelastic properties of ε-Fe2O3 to be investigated as functions of temperature and magnetic field strength by Resonant Ultrasound Spectroscopy in the frequency range ∼0.1–1 MHz. Formal analysis of spontaneous strains, e, from previously obtained high resolution lattice parameter data confirmed that magnetic ordering below ∼500 K is accompanied by strains of up to ∼±0.002 due to coupling with the order parameter, m, according to λem2. However, this coupling does not result in elastic softening that would be expected if the order parameter relaxed in response to an induced strain on the timescale of the acoustic resonances. Stiffening or softening during heating through ∼450–480 K of the initial as prepared material, which acquired a distinct magnetisation parallel to the stress applied during Spark Plasma Sintering, is attributed to changes in magnetic domain configurations involving preferred local alignments of individual moments of monodomain crystals. The crystallographic space group, Pna21, and magnetic space group at room temperature, Pna'21', allow ε-Fe2O3 to be both piezoelectric and piezomagnetic. It is postulated that changes in the effective coefficients of these properties for bulk samples are responsible for the observed variations in acoustic resonance frequencies according to the magnetic domain structure present. No elastic or anelastic anomalies were observed at the commensurate-incommensurate transition near 110 K. Instead, acoustic resonance frequencies changed in response to an applied magnetic field, consistent with viscous motion of magnetic domain walls and the effect of poling on piezo coefficients. Ceramic samples of ε-Fe2O3 could have potentially functional piezoelectric and/or piezomagnetic properties that are tunable by choice of magnetic and thermal history.
AB - Preparation of a ceramic sample which preserved the nanoscale grain sizes of ∼10–30 nm has allowed elastic and anelastic properties of ε-Fe2O3 to be investigated as functions of temperature and magnetic field strength by Resonant Ultrasound Spectroscopy in the frequency range ∼0.1–1 MHz. Formal analysis of spontaneous strains, e, from previously obtained high resolution lattice parameter data confirmed that magnetic ordering below ∼500 K is accompanied by strains of up to ∼±0.002 due to coupling with the order parameter, m, according to λem2. However, this coupling does not result in elastic softening that would be expected if the order parameter relaxed in response to an induced strain on the timescale of the acoustic resonances. Stiffening or softening during heating through ∼450–480 K of the initial as prepared material, which acquired a distinct magnetisation parallel to the stress applied during Spark Plasma Sintering, is attributed to changes in magnetic domain configurations involving preferred local alignments of individual moments of monodomain crystals. The crystallographic space group, Pna21, and magnetic space group at room temperature, Pna'21', allow ε-Fe2O3 to be both piezoelectric and piezomagnetic. It is postulated that changes in the effective coefficients of these properties for bulk samples are responsible for the observed variations in acoustic resonance frequencies according to the magnetic domain structure present. No elastic or anelastic anomalies were observed at the commensurate-incommensurate transition near 110 K. Instead, acoustic resonance frequencies changed in response to an applied magnetic field, consistent with viscous motion of magnetic domain walls and the effect of poling on piezo coefficients. Ceramic samples of ε-Fe2O3 could have potentially functional piezoelectric and/or piezomagnetic properties that are tunable by choice of magnetic and thermal history.
KW - Magnetic phase transition
KW - Magnetoelastic coupling
KW - Nanocrystalline
KW - Strain relaxation
KW - ε-Fe O
UR - http://www.scopus.com/inward/record.url?scp=85160034491&partnerID=8YFLogxK
U2 - 10.1016/j.jmmm.2022.170240
DO - 10.1016/j.jmmm.2022.170240
M3 - Article
VL - 583
JO - Journal of Magnetism and Magnetic Materials
JF - Journal of Magnetism and Magnetic Materials
SN - 0304-8853
M1 - 170240
ER -