Kenta Kimura

We have grown single crystals of a triangular lattice antiferromagnet (TLA), ${\text{CuCrO}}_{2}$, and investigated the correlation between magnetic and dielectric properties. Two magnetic phase transitions are observed at ${T}_{\text{N}2}\ensuremath{\approx}24.2\text{ }\text{K}$ and ${T}_{\text{N}1}\ensuremath{\approx}23.6\text{ }\text{K}$. It was found that ferroelectric polarization along the triangular lattice plane develops at ${T}_{\text{N}1}$, suggesting that the system undergoes a transi

The effects of electric and magnetic fields on magnetic and electric properties have been investigated for a triangular lattice antiferromagnet CuCrO(2) showing magnetically induced ferroelectric order. We demonstrate that ferroelectric polarization reversal can be finely tuned by using both magnetic and electric fields in the triangular lattice antiferromagnet. The observed magnetoelectric tunability can be attributed to small in-plane spin anisotropy and a resultant high degree of freedom for

Several pyrochlore antiferromagnets are being considered as candidate materials where geometrical frustration may lead to quantum spin-liquid states. In a ``breathing'' pyrochlore lattice systems (see PRL 110, 097203 (2013)) the spins occupy the vertices of alternating tetrahedra of different size that are characterized by different exchange parameters $J$ and ${J}^{\ensuremath{'}}$.

We investigated magnetostrictive properties of a triangular lattice antiferromagnet CuCrO 2 showing an incommensurate proper-screw spin order by means of x-ray diffraction and strain gauge measurements. A deformation of the triangular lattice plane leading to a lowered crystallographic symmetry was found upon the magnetic ordering, which demonstrates a strong spin–lattice coupling in this system. The resultant multiple structural domains can be successfully arranged by magnetic field cooling pro

In vortex-like spin arrangements, multiple spins can combine into emergent multipole moments. Such multipole moments have broken space-inversion and time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME) activity. Three types of such multipole moments are known: toroidal; monopole; and quadrupole moments. So far, however, the ME activity of these multipole moments has only been established experimentally for the toroidal moment. Here we propose a magnetic square cupola c

Abstract Parity-odd magnetoelectric multipoles such as magnetic quadrupoles and toroidal dipoles contribute to various symmetry-dependent magnetic phenomena and formation of exotic ordered phases. However, the observation of domain structures emerging due to symmetry breaking caused by these multipoles is a severe challenge because of their antiferromagnetic nature without net magnetization. Here, we report the discovery of nonreciprocal linear dichroism for visible light (~4% at 1.8 eV) in a ma

Single crystals of two novel tetragonal chiral materials, A(TiO)Cu4(PO4)4 (A = Ba, Sr), were grown from Na2Mo2O7 flux, and their crystal and chiral domain structures were characterized. Polarized-light microscopy studies of the chiral domain structures in the crystals show that Ba(TiO)Cu4(PO4)4 mostly hosts a multidomain state, while a monodomain state predominantly appears in Sr(TiO)Cu4(PO4)4. To explain this striking difference, we quantified the chirality strength of these materials by compar

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 B

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 substantiat

Abstract The subject of ultrafine metallic particles is treated with emphasis on energy level statistics. The energy level statistics so far proposed are reviewed based on the effect of shape of particles. The deviation of the nature of the chemical bond and that of magnetic properties in small size systems from those of bulk is described. The relevant electronic properties are expressed by formulae that incorporate the effect of shape in addition to size. New and old experiments including NMR K

Abstract Chiral-lattice magnets can exhibit a variety of physical phenomena when time-reversal symmetry is broken by their magnetism. For example, nonreciprocal responses of (quasi)particles have been widely observed in chiral-lattice magnets with macroscopic magnetization. Meanwhile, time-reversal symmetry can also be broken in antiferromagnets without magnetization. Here we report an unconventional chirality-magnetism coupling in a chiral-lattice antiferromagnet Pb(TiO)Cu 4 (PO 4 ) 4 whose tim

A magnetic structural unit with asymmetric geometry may be a source for symmetry-dependent unique phenomena such as the magnetoelectric effect. The authors report the discovery of ferroelectricity and a magnetic-field-induced sign reversal of ferroelectric polarization in Pb(TiO)Cu${}_{4}$(PO${}_{4}$)${}_{4}$, whose structure is characterized by a staggered array of Cu${}_{4}$O${}_{12}$ magnetic units with convex geometry known as square cupola. Their model and first-principles calculations reve