Tuning the Néel Temperature of Hexagonal Ferrites by Structural Distortion

Abstract

To tune the magnetic properties of hexagonal ferrites, a family of magnetoelectric multiferroic materials, by atomic-scale structural engineering, we studied the effect of structural distortion on the magnetic ordering temperature (TN). Using the symmetry analysis, we show that unlike most antiferromagnetic rareearth transition-metal perovskites, a larger structural distortion leads to a higher TN in hexagonal ferrites and manganites, because the K3 structural distortion induces the three-dimensional magnetic ordering, which is forbidden in the undistorted structure by symmetry. We also revealed a near-linear relation between TN and the tolerance factor and a power-law relation between TN and the K3 distortion amplitude. Following the analysis, a record-high TN (185 K) among hexagonal ferrites was predicted in hexagonal ScFeO3 and experimentally verified in epitaxially stabilized films. These results add to the paradigm of spin-lattice coupling in antiferromagnetic oxides and suggests further tunability of hexagonal ferrites if more lattice distortion can be achieved.

Interplay of Magnetic Properties and Doping in Epitaxial Films of h‐REFeO3 Multiferroic Oxides

“…[10,13] It was proposed that strain/ stress engineering of the hexagonal films will duly change the c/a ratio in lattice, enabling to achieve T N values above 200 K. [9] Structural distortion in epitaxially grown h-ScFeO 3 films was used to increase the K 3 phonon mode amplitude, the high measured T N of the film was correlated to lattice distortion. [8,14] The work confirmed the importance of spin-lattice coupling in manipulation of ferroic properties in lattices of h-REFeO 3 , as in their counterparts the h-REMnO 3 lattices. [15] Beside of Neel ordering temperature, additional magnetic contributions below T N have been observed in both bulk and thin films of the hexagonal lattice, with origin attributed to spin reorientation.…”

“…[17] Values of c-axis of 11.690 or 11.710 Å were reported for thin films of ScFeO 3 deposited on ALO, where Sc has smaller ionic radii than Lu. [8,18] The films of LuFeO 3 deposited on YSZ substrates with different techniques show smaller out of plane lattice constants, 11.750, 11.700, and 11.810 Å as to be compared to the films grown on ALO substrate. [9,19] In current work, for the substrate with smaller in-plane lattice constant, ALO (4.749 Å), the present results indicate that doping of Lu with Sc results in shrinkage of the out of plane lattice constant of the Lu 0.5 Sc 0.5 FeO 3 thin film compared to the pure LuFeO 3 or ScFeO 3 .…”

“…Density functional (DFT) based calculations and limited experimental work have shown the feasibility to tune multiferroic properties in the structure of the h-RE(Mn, Fe)O 3 with chemical pressure, stress/strain engineering or hydrostatic pressure. [5][6][7][8] Intensive research is undergoing in the hexagonal RE(Fe,Mn) O 3 multiferroics to rise T N closer to room temperature. Stabilization of the hexagonal form was shown to be possible in the bulk state via chemical doping, [9,10] high pressure synthesis, [11] or sol-gel preparation.…”

DEMAND, a Dimensional Extreme Magnetic Neutron Diffractometer at the High Flux Isotope Reactor

“…For tiny crystals with perfect quality (the mosaic is instrument-resolution-limited), all of the reflections can be snapshotted and corrected by the instrument resolution. The smallest crystal that has been measured at HB-3A is an YbFeO 3 hexagonal ferrite thin film (5 mm × 5 mm × 50 nm~0.001 mm 3 ), and the ordered Fe-moment size determined was 2 µ B [13]. The weak superlattice peaks originating from an Fe/Cu site order in a superconductor material NaCuFeAs were also collected by snapshotting Bragg peaks at HB-3A, and the refinement confirmed that it is a Fe/Cu stripe structure.…”

Synthesis and Properties of Ferrite-Based Nanoparticles

“…One of the promising candidates in modern alternative energy as the basis of solid fuel elements are perovskite-like systems based on RFeO 3 ferrite (R = Ce, Y, Ba, Sr) [14,15,16,17,18]. The increased interest in this class of structures is due to their distorted crystal structure with the possibility of filling vacancies with equivalent iron ions [19], which has an essential impact on the structural, optical, magnetic, and dielectric properties [20,21,22,23].…”