Page 28 - ILL Annual Report 2019

MAGNETISM
Xabier Martínez de Irujo Labalde. Spanish Department of Inorganic Chemistry,
Faculty of Chemistry, Complutense University
of Madrid, Spain
‘I was awarded my PhD from the University Complutense in Madrid, in 2019. My research interests are the magnetic, electric and ultimately
magneto-electric properties in perovskite-related transition metal oxides. Neutron diffraction is an ideal tool for establishing the nuclear and magnetic structures of these complex systems.’
Multiferroism induced by spontaneous structural ordering in antiferromagnetic iron-perovskites
High-intensity two-axis diffractometer with variable resolution D20
AUTHORS
X. Martinez de Irujo-Labalde and S. Garcia-Martin (Universidad Complutense, Madrid, Spain)
U. Amador (Universidad San Pablo-CEU, Madrid, Spain)
C. Ritter (ILL)
ARTICLE FROM
Chem. Mater. (2019)—doi: https://doi.org/10.1021/acs. chemmater.9b02716
REFERENCES
[1] X. Martínez de Irujo-Labalde, M. Goto, E. Urones-Garrote,
U. Amador, C. Ritter, M.E. Amano Patino, A. Koedtruad, Z. Tan, Y. Shimakawa and S. Garcia-Martin, Chem. Mater. 31 (2019)
The magnetic and nuclear structure of the oxide Tb0.8Ba0.8Ca0.4Fe2O8, as a non-absorbing representative, was determined using the high-intensity powder diffractometer D20 and the high-resolution diffractometer D2B. A sample was placed inside a quartz tube open
to the air to avoid oxygen loss on heating in a furnace
at between room temperature and 1 000 K. Figure 1a shows part of the high-resolution data taken at 300 K and 1 000 K, with the background of the quartz tube removed.
The Tb1.2Ba1.2Ca0.6Fe3O8 oxide presents a layered-type perovskite structure with a √2ap x √2bp x 3cp unit cell (Pb21m space group) related to the layered-ordering
of A-cations in a Tb/Ca-Tb/Ca-Ba-Tb/Ca sequence with a combined T-O-O-T ordering sequence of the
Fe-O polyhedra. The polar space group Pb21m of the oxide allows the existence of a net polarisation from uncompensated shifts of the ions within the structure, giving a polar moment of 23.2 μC/cm2 along the b-axis. Figure 2a shows the unit cell of the crystal structure indicating polarisation associated with the atom displacements in the b direction.
Figure 1
a) PND patterns of Tb1.2Ba1.2Ca0.6Fe3O8 taken at below (300 K) and above
(1 000 K) the magnetic transition. The arrows indicate the magnetic reflections.
b) Temperature dependence of the magnetic moment of Fe in the octahedral (black) and tetrahedral (red) sites of Tb1.2Ba1.2Ca0.6Fe3O8.
Perovskite-based compounds of type RE Ba Ca Fe O adopt a layered
1.2 1.2 0.6
arrangement of Re, Ba and Ca atoms,
3 8
which induces FeO4-tetrahedra (T) and
FeO -octahedra (O) ordering in a polar 6
crystal structure and antiferromagnetic ordering of Fe3+ up to 850 K. The combination of magnetic and polar properties results in a multiferroic oxide at room temperature. The nuclear structure
of these oxides has been revealed by transmission electron microscopy techniques with atomic resolution [1], while the magnetic structure has been determined
by neutron diffraction experiments.
ANNUAL REPORT 2019