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Register a new userElectromagnon in ferrimagnetic eps-Fe2O3 nanograin ceramics
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Electromagnons are known from multiferroics as spin waves excited by the electric component of electromagnetic radiation. We report the discovery of an excitation in the far-infrared spectra of eps-Fe2O3 which we attribute to an electromagnon appearing below 110 K, where the ferrimagnetic structure becomes incommensurately modulated. Inelastic neutron scattering shows that the electromagnon energy corresponds to that of a magnon from the Brillouin zone boundary. Dielectric measurements did not reveal any sign of ferroelectricity in eps-Fe2O3 down to 10 K, despite its acentric crystal structure. This shows that the activation of an electromagnon requires, in addition to the polar ferrimagnetic structure, a modulation of the magnetic structure. We demonstrate that a combination of inelastic neutron scattering with infrared and / or terahertz spectroscopies allows detecting electromagnons in ceramics, where no crystal-orientation analysis of THz and infrared spectra is possible.
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We investigated static and dynamic magnetoelectric properties of single crystalline BaSrCoZnFe$_{11}$AlO$_{22}$ which is a room-temperature multiferroic with Y-type hexaferrite crystal structure. Below $300,rm K$, a purely electric-dipole-active electromagnon at $approx 1.2,rm THz$ with the electric polarization oscillating along the hexagonal axis was observed by THz and Raman spectroscopies. We investigated the behavior of the electromagnon with applied DC magnetic field and linked its properties to static measurements of the magnetic structure. Our analytical calculations determined selection rules for electromagnons activated by the magnetostriction mechanism in various magnetic structures of Y-type hexaferrite. Comparison with our experiment supports that the electromagnon is indeed activated by the magnetostriction mechanism involving spin vibrations along the hexagonal axis.
We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at T_C1=475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above T_C1. Step-like dielectric anomaly observed at T_C1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of P. Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic, but only antipolar ferromagnet.
We investigate the spin Hall magnetoresistance (SMR) at room temperature in thin film heterostructures of antiferromagnetic, insulating, (0001)-oriented alpha-Fe2O3 (hematite) and Pt. We measure their longitudinal and transverse resistivities while rotating an applied magnetic field of up to 17T in three orthogonal planes. For out-of-plane magnetotransport measurements, we find indications for a multidomain antiferromagnetic configuration whenever the field is aligned along the film normal. For in-plane field rotations, we clearly observe a sinusoidal resistivity oscillation characteristic for the SMR due to a coherent rotation of the Neel vector. The maximum SMR amplitude of 0.25% is, surprisingly, twice as high as for prototypical ferrimagnetic Y3Fe5O12/Pt heterostructures. The SMR effect saturates at much smaller magnetic fields than in comparable antiferromagnets, making the alpha-Fe2O3/Pt system particularly interesting for room-temperature antiferromagnetic spintronic applications.
Two-dimensional (2D) multiferroics exhibit cross-control capacity between magnetic and electric responses in reduced spatial domain, making them well suited for next-generation nanoscale devices; however, progress has been slow in developing materials with required characteristic properties. Here we identify by first-principles calculations robust 2D multiferroic behaviors in decorated Fe2O3 monolayer, showcasing N@Fe2O3 as a prototypical case, where ferroelectricity and ferromagnetism stem from the same origin, namely Fe d-orbit splitting induced by the Jahn-Teller distortion and associated crystal field changes. The resulting ferromagnetic and ferroelectric polarization can be effectively reversed and regulated by applied electric field or strain, offering efficient functionality. These findings establish strong materials phenomena and elucidate underlying physics mechanism in a family of truly 2D multiferroics that are highly promising for advanced device applications.
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