Conventional magnetic memories rely on bistable magnetic states, such as the up and down magnetization states in ferromagnets. Increasing the number of stable magnetic states in each cell, preferably ...composed of antiferromagnets without stray fields, promises to achieve higher-capacity memories. Thus far, such multi-stable antiferromagnetic states have been extensively studied in conducting systems. Here, we report on a striking optical response in the magnetoelectric collinear antiferromagnet Bi
CuO
, which is an insulating version of the representative spintronic material, CuMnAs, with four stable Néel vector orientations. We find that, due to a magnetoelectric effect in a visible range, which is enhanced by a peculiar local environment of Cu ions, absorption coefficient takes three discrete values depending on an angle between the propagation vector of light and the Néel vector-a phenomenon that we term antiferromagnetic trichroism. Furthermore, using this antiferromagnetic trichroism, we successfully visualize field-driven reversal and rotation of the Néel vector.
Ferroaxial order, which is characterized by a vortex of electric dipole moments, is attracting more attention in terms of a new category of ferroic order. Here we propose that the disodium hafnium ...borate, Na2Hf(BO3)2, shows ferroaxial order that is stabilized by the second-order Jahn–Teller (SOJT) effect. Furthermore, the dipotassium hafnium borate, K2Hf(BO3)2, the synthesis of which has never been reported previously, is predicted to have a nonferroaxial ground state from the perspective of the SOJT effect. This prediction is demonstrated through our structural refinements on polycrystalline samples and our first-principles calculations with representation theory. This study offers a chemical perspective for developing new ferroaxial materials and controlling their ferroaxial order.
In a chiral medium, any mirror symmetries are broken, which induces unique physical properties represented by natural optical rotation. When electromagnetic waves propagate through a chiral medium ...placed in a magnetic field, the refractive index, or equivalently, the absorption encountered by the electromagnetic waves differs depending on whether it travels parallel or antiparallel to the magnetic field. Such a phenomenon is known as magnetochiral dichroism (MChD), which is the characteristic interplay between chirality and magnetism. Similar to chirality, the so-called ferroaxial order, an emergent ferroic state of crystalline materials, is also characterized by mirror symmetry breaking. In contrast to chiral materials, however, the mirror symmetry perpendicular to the crystalline principal axis is allowed in ferroaxial materials. In other words, chirality and thus phenomena unique to chirality can be induced by breaking the remaining mirror symmetry by applying an electric field. Here, we show electric control of chirality and resulting electric field-induced MChD (
-MChD) of the short-wavelength infrared region in a ferroaxial crystal, NiTiO
. We performed spectroscopy measurements of
-MChD by taking a difference of absorption coefficients obtained with and without electric and magnetic fields. As a result,
-MChD was observed around the excitation energy corresponding to Ni
magnetic-dipole transitions. The result is nicely explained by adopting the theory of MChD concerning the pseudo-Stark splitting of the energy state. Ferroaxial materials therefore provide platforms to achieve electric control of chirality-related phenomena.
Phonon polaritons-light coupled to lattice vibrations-in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field ...confinement, anisotropic propagation and ultra-long lifetime in the picosecond range
. However, the lack of tunability of their narrow and material-specific spectral range-the Reststrahlen band-severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-V
O
enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps). We expect our intercalation method to be applicable to other van der Waals crystals, opening the door for the use of phonon polaritons in broad spectral bands in the mid-infrared domain.
Nonreciprocal directional dichroism (NDD) is a phenomenon in which the optical absorption is changed by reversing the direction of light propagation or the sign of the magnetic order parameters. ...While the NDD has mostly been observed in materials with macroscopic magnetization, recent experiments have shown that the NDD can be induced by a specific antiferromagnetic (AFM) spin structure that breaks both space-inversion and time-reversal symmetries. This opens the possibility of visualizing the spatial distribution of AFM domains via the NDD effect. This article reviews the basic features of the NDD, a brief history of the NDD in AFM materials, and recent achievements in visualizing AFM domains via the NDD and related optical responses, and finally provides a perspective on applications of this method for future AFM spintronics research.
Switching crystallographic chirality is nontrivial because there is no simple conjugate field to chirality. Here we demonstrate chirality switching in an inorganic crystalline material by ...manipulating the boundaries of chiral domains with laser irradiation. Our study material is Ba(TiO)Cu4(PO4)4, exhibiting a chiral structure at room temperature and a chiral–achiral phase transition at 710 °C. By irradiation of a laser beam with a wavelength at which Ba(TiO)Cu4(PO4)4 exhibits strong optical absorption, local heating is induced. This leads to reconstructions of chiral domain boundaries, revealed by optical rotation measurements. In the reconstruction process, energetically unstable domain boundaries tend to be minimized, affecting resultant domain patterns. On the basis of this feature, we successfully manipulate chiral domain patterns by scanning the laser beam on the sample surface. Our findings provide a unique approach to controlling chirality in inorganic crystalline materials.
Ferrochiral transition, i.e., a transition involving an emergence of chirality, provides an unique opportunity to achieve a nonvolatile reversible control of chirality with external fields. However, ...materials showing pure ferrochiral transitions, which are accompanied by no other types of ferroic transition, are exceedingly rare. In this study, we propose that a pure ferrochiral transition is achieved by a combination of antipolar and antiferroaxial orderings of structural units, and substantiate this proposal through a study of the chiral compound Ba(TiO)Cu4(PO4)4. Single crystal X-ray diffraction measurements have revealed that this material undergoes a second order ferrochiral transition whose order parameter is described by an antiferroaxial (staggered) rotation of antipolar structural units, thus demonstrating our proposal. Furthermore, by measuring spatial distributions of optical rotation, we successfully visualized a temperature evolution of ferrochiral domains across the transition temperature and demonstrated the relationship between chirality and optical rotation. This work provides a guide to find a pure ferrochiral transition, thus providing an opportunity to achieve a ferroic control of chirality.
One of the problems in dental implant treatment is the lack of periodontal ligament (PDL), which supports teeth, prevents infection, and transduces sensations such as chewiness. The objective of the ...present study was to develop a decellularized PDL for supporting an artificial tooth. To this end, we prepared mouse decellularized mandible bone with a PDL matrix by high hydrostatic pressure and DNase and detergent treatments and evaluated its reconstruction in vivo. After tooth extraction, the decellularized mandible bone with PDL matrix was implanted under the subrenal capsule in rat and observed that host cells migrated into the matrix and oriented along the PDL collagen fibers. The extracted decellularized tooth and de- and re-calcified teeth, which was used as an artificial tooth model, were re-inserted into the decellularized mandible bone and implanted under the subrenal capsule in rat. The reconstructed PDL matrix for the extracted decellularized tooth resembled the decellularized mandible bone without tooth extraction. This demonstrates that decellularized PDL matrix can reconstruct PDL tissue by controlling host cell migration, which could serve as a novel periodontal treatment approach.
The so-called ferroaxial transition characterized by a rotational structural distortion that breaks a mirror symmetry has gained growing interest in terms of a new class of ferroic state in ...crystalline materials. RbFe(MoO4)2, which belongs to glaserite-type compounds, X (□;1) Y (□;2)M(TO4)2, is one of the most representative materials showing a ferroaxial transition, i.e., ferroaxial materials. Considering a variety of glaserite-type compounds, we expect that they provide a good arena for ferroaxial materials. In this work, we explored new ferroaxial materials by formula-based screening using a regular expression search and the symmetry detection algorithm. As a result, we found that a glaserite-type compound, K2Zr(PO4)2, is one of the promising candidates for ferroaxial materials. Experimentally, we demonstrate that K2Zr(PO4)2 shows a ferroaxial transition at about 700 K, which is well explained by ab initio phonon calculations. The ferroaxial nature of K2Zr(PO4)2 is further confirmed by the observation of its domain structures using a linear electrogyration effect, i.e., optical rotation in proportion to an applied electric field. Our work provides an effective approach to exploring ferroaxial materials.
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