RESUMEN
The core and surface structure, and magnetism of mechano-synthesized LaFeO3 nanoparticles (30-40 nm), Eu3+-doped (La0.70Eu0.30FeO3), and Eu3+/Cr3+ co-doped (La0.70Eu0.30Fe0.95Cr0.05O3) are reported. Doping results in a transition from the O'-type to the O-type distorted structure. Traces of reactants, intermediate phases, and a small amount of Eu2+ ions were detected on the surfaces of the nanoparticles. The nanoparticles consist of antiferromagnetic cores flanked by ferromagnetic shells. The Eu3+ dopant ions enhance the magnetization values relative to those of the pristine nanoparticles and result in magnetic susceptibilities compatible with the presence of Eu3+ van Vleck paramagnetism of spin-orbit coupling constant (λ = 363 cm-1) and a low temperature Curie-Weiss like behavior associated with the minority Eu2+ ions. Anomalous temperature-dependent magnetic hardening due to competing magnetic anisotropy and magnetoelectric coupling effects together with a temperature-dependent dopant-sensitive exchange bias, caused by thermally activated spin reversals at the core of the nanoparticles, were observed.
RESUMEN
B-site cobalt (Co)-doped rare-earth orthoferrites ReFeO3 have shown considerable enhancement in physical properties compared to their parent counterparts, and Co-doped LuFeO3 has rarely been reported. In this work, LuFe1-xCoxO3 (x = 0, 0.05, 0.1, 0.15) powders have been successfully prepared by a mechanochemical activation-assisted solid-state reaction (MAS) method at 1100 °C for 2 h. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies demonstrated that a shrinkage in lattice parameters emerges when B-site Fe ions are substituted by Co ions. The morphology and elemental distribution were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The UV-visible absorbance spectra show that LuFe0.85Co0.15O3 powders have a narrower bandgap (1.75 eV) and higher absorbance than those of LuFeO3 (2.06 eV), obviously improving the light utilization efficiency. Additionally, LuFe0.85Co0.15O3 powders represent a higher photocatalytic capacity than LuFeO3 powders and can almost completely degrade MO in 5.5 h with the assistance of oxalic acid under visible irradiation. We believe that the present study will promote the application of orthorhombic LuFeO3 in photocatalysis.
RESUMEN
The structure and the physical phenomena that occur in a crystal can be described by using a suitable set of symmetry-adapted modes. The classification of magnetic modes in crystals presented in Fabrykiewicz et al. [Acta Cryst. (2021), A77, 327-338] is extended to a classification of electric and toroidal (anapole) modes in crystals. These three classifications are based on magnetic point groups, which are used in two contexts: (i) the magnetic point group of the magnetic crystal class and (ii) the magnetic site-symmetry point group of the Wyckoff position of interest. The classifications for magnetic, electric and toroidal modes are based on the properties of the three generalized inversions: space inversion 1, time inversion 1' and the space-and-time inversion 1'. It is emphasized that none of these three inversions is more important than the other two. A new notation for symmetry operation symbols and magnetic point group symbols is proposed; each operation is presented as a product of one proper rotation and one generalized inversion. For magnetic, electric and toroidal orderings there are 64 modes: three pure ferro(magnetic/electric/toroidal) modes, 13 mixed ferro(magnetic/electric/toroidal) and antiferro(magnetic/electric/toroidal) modes, and 48 pure antiferro(magnetic/electric/toroidal) modes. The proposed classification of modes leads to useful observations: the electric and toroidal modes have many symmetry limitations similar to those already known for the magnetic modes, e.g. a continuous reorientation of the magnetic or electric or toroidal moments is possible only in triclinic or monoclinic symmetry. An antiferro(magnetic/electric/toroidal) ordering with a weak perpendicular ferro(magnetic/electric/toroidal) component is possible only in monoclinic or orthorhombic symmetry. The general classifications of magnetic, electric and toroidal modes are presented for the case of NdFeO3.
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We employ synchrotron-based near-field infrared spectroscopy to image the phononic properties of ferroelectric domain walls in hexagonal (h) Lu0.6Sc0.4FeO3, and we compare our findings with a detailed symmetry analysis, lattice dynamics calculations, and prior models of domain-wall structure. Rather than metallic and atomically thin as observed in the rare-earth manganites, ferroelectric walls in h-Lu0.6Sc0.4FeO3 are broad and semiconducting, a finding that we attribute to the presence of an A-site substitution-induced intermediate phase that reduces strain and renders the interior of the domain wall nonpolar. Mixed Lu/Sc occupation on the A site also provides compositional heterogeneity over micron-sized length scales, and we leverage the fact that Lu and Sc cluster in different ratios to demonstrate that the spectral characteristics at the wall are robust even in different compositional regimes. This work opens the door to broadband imaging of physical and chemical heterogeneity in ferroics and represents an important step toward revealing the rich properties of these flexible defect states.
RESUMEN
High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO3. The transition from the high temperaturek= 0 Γ4(GxAyFz) to the low temperature Γ1(AxGyCz) type order of the Fe-sublattice is found atTSR= 73 K and does not show any thermal hysteresis. BelowTN2= 4 K the Dy-sublattice orders in an incommensurate magnetic structure withk= [0, 0, 0.028] while the Fe-sublattice keeps its commensurate Γ1type order. DyFeO3is the first orthoferriteRFeO3to possess an incommensurate magnetic order of the rare earth sublattice under zero field conditions; an important piece of information neglected in the recent discussion of its multiferroic properties.
RESUMEN
Metamaterials display many electromagnetic properties, such as the manipulation of electromagnetic waves through the arrangement of small discrete structures. However, complex designs of mechanically or electrically patterned structures are required to modify these properties. We report on the use of rare earth orthoferrites to tune transmitted waves by engineering the thickness, composition, and temperature using terahertz (THz) time-domain spectroscopy. The modeling of the process of manipulating the transmitted waves helps to elucidate the manipulated amplitude, transmittance, peak height, and frequency. The effectiveness of thickness engineering in tuning the transmitted waves, which conformed to the Beer-Lambert law, was demonstrated. The transmitted waves were also strongly affected by doping. In addition, a thermal anisotropic energy manipulation approach to tuning transmitted waves was developed by lowering the temperature. Rare earth orthoferrites are a kind of effective medium in the THz range and exhibit the signature of natural metamaterials.
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We investigate the detailed analysis of the magnetic properties in a series of Pr1-xSmxFeO3single crystals fromx= 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperatureTSRΓ4(Gx,Ay,Fz) to Γ2(Fx,Cy,Gz) covers a wide temperature range including room temperature. A 'butterfly'-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points inx= 0.4 to 0.8 compounds. Interestingly, in Pr0.6Sm0.4FeO3single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr3+-Fe3+and Sm3+-Fe3+exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.
RESUMEN
High resolution and high intensity neutron powder diffraction are used to determine the temperature dependence of the crystallographic and magnetic structure of the orthoferrite CeFeO3. The high temperatureGx-type magnetic coupling of the Fe-sublattice described by the Γ4(GxAyFz) irreducible representation changes at the spin reorientation temperatureTSR= 228 K to aGy-type coupling of Γ1(AxGyCz). The spin reorientation is of first order and sees a hysteresis of about 2.5 K atTSR. Below 35 K faint magnetic peaks reflectingCztype magnetic coupling appear and are argued to be related to the Ce-sublattice. Magnetic moments at 2 K amount toµFe= 4.15 µBandµCe= 0.11 µB. CeFeO3is only the secondRFeO3compound after DyFeO3showing this ground state magnetic structure of the Fe-sublattice. The orthorhombic structurePbnmis kept over the whole temperature range.
RESUMEN
Exclusive magnetocaloric properties of orthoferrites offer advantages for their application in the magnetic hyperthermia as well as imaging applications. In the present study, the effect of yttrium concentration on the magnetic characteristics of the iron oxide based nanomaterials was analyzed to assess their potential for the hyperthermia applications. The Sol-gel method was used to synthesize the Yttrium Iron Garnet (YIG) based nanoparticles, using different molar ratios of Fe and Y precursors, followed by the calcination at 900, 1000 and 1100 °C. XRD analysis determined the formation of the pure phase of yttrium iron garnet Y3Fe5O12 (YIG) at 0.5 molar ratio of yttrium at all the calcination temperatures and pure phase of yttrium iron perovskite YFeO3 (YIP) for 1 molar ratio of yttrium at 1000 and 1100 °C. The mean particle size was observed in the range of 100 to 400 nm. The magnetic characterization studies showed the highest saturation magnetization for the sample containing 0.5 molar ratio of the yttrium calcinated at 1000 °C. The magnetization values were linearly related to the contents of YIG phases in the synthesized samples. Induction heating of YIG resulted in the hyperthermia temperature (42 to 44 °C) in 13 min with the SAR values 114.65 W/g at 1 mg/ml. The prepared samples showed no in-vitro toxic effects on the MG63 cells (>90% cell viability). In addition, in-vitro treatment at hyperthermia temperature for 15 min reduced cell viability of cancer cells (A549) to 55%, while no toxic effect was observed on MG 63 cells. The present study postulates Yttrium Iron Garnet as an effective therapeutic agent for hyperthermia cancer treatment.