arXiv subjects

N. Abe

Publications and source records attributed to N. Abe.

6 recordsLinked to original sources

arXiv2018

Room-temperature Low-field Colossal Magneto-resistance in Double-perovskite Manganite

The gigantic decrease of resistance by an applied magnetic field, which is often referred to as colossal magnetoresistance (CMR), has been an attracting phenomenon in strongly correlated electron systems. The discovery of CMR in manganese oxide compounds has developed the science of strong coupling among charge, orbital, and spin degrees of freedom. CMR is also attracting scientists from the viewpoint of possible applications to sensors, memories, and so on. However, no application using CMR effect has been achieved so far, partly because the CMR materials which satisfy all of the required conditions for the application, namely, high operating temperature, low operating magnetic field, and sharp resistive change, have not been discovered. Here we report a resistance change of more than two-orders of magnitude at a magnetic field lower than 2 T near 300 K in an A-site ordered NdBaMn_2_O_6_ crystal. When temperature and a magnetic field sweep from insulating (metallic) phase to metallic (insulating) phase, the insulating (metallic) conduction changes to the metallic (insulating) conduction within 1 K and 0.5 T, respectively. The CMR is ascribed to the melting of the charge ordering. The entropy change which is estimated from the B-T phase diagram is smaller than what is expected for the charge and orbital ordering. The suppression of the entropy change is attributable to the loss of the short range ferromagnetic fluctuation of Mn spin moments, which an important key of the high temperature and low magnetic field CMR effect.

cond-mat.str-el↗

arXiv2016

Gigantic directional asymmetry of luminescence in multiferroic CuB2O4

We report direction dependent luminescence (DDL), i.e., the asymmetry in the luminescence intensity between the opposite directions of the emission, in multiferroic CuB2O4. Although it is well known that the optical constants can change with the reversal of the propagation direction of light in multiferroic materials, the largest asymmetry in the luminescence intensity was 0.5 % so far. We have performed a measurement of photoluminescence with a He-Ne laser irradiation (633 nm). The luminescence intensity changes by about 70 % with the reversal of the magnetic field due to the interference between the electric dipole and magnetic dipole transitions. We also demonstrate the imaging of the canted antiferromagnetic domain structure of (Cu,Ni)B2O4 by using the large DDL.

cond-mat.mtrl-sci↗

arXiv2014

Visualization of ferroelectric domains in boracite using emission of terahertz radiation

We report on the emission of terahertz radiation by irradiation of femtosecond laser pulses in non-centrosymmetric paraelectric and ferroelectric phases of Co$_3$B$_7$O$_{13}$I boracite. The Generation of the terahertz waves in both phases is caused by optical rectification via a second-order nonlinear optical effect. In the ferroelectric phase, we successfully visualized ferroelectric domains by analyzing the polarization state of the terahertz wave radiated from the crystal. In a large area of the crystal ($\sim$ 500 $\times$ 500 $μ$m$^2$), the observed polarization vector of the radiated terahertz wave was tilted from directions of spontaneous polarization, i.e., [100]$_{\rm cub}$, [010]$_{\rm cub}$, and [001]$_{\rm cub}$ in cubic setting, which can be explained by the presence of a ferroelectric 90$^\circ$ domain wall of the (101)$_{\rm cub}$ plane.

cond-mat.mtrl-sci↗

arXiv2013

Magnetization of SrCu2(BO3)2 in ultrahigh magnetic fields up to 118 T

The magnetization process of the orthogonal-dimer antiferromagnet SrCu2(BO3)2 is investigated in high magnetic fields of up to 118 T. A 1/2 plateau is clearly observed in the field range 84 to 108 T in addition to 1/8, 1/4 and 1/3 plateaux at lower fields. Using a combination of state-of-the-art numerical simulations, the main features of the high-field magnetization, a 1/2 plateau of width 24 T, a 1/3 plateau of width 34 T, and no 2/5 plateau, are shown to agree quantitatively with the Shastry-Sutherland model if the ratio of inter- to intra-dimer exchange interactions J'/J=0.63. It is further predicted that the intermediate phase between the 1/3 and 1/2 plateau is not uniform but consists of a 1/3 supersolid followed by a 2/5 supersolid and possibly a domain-wall phase, with a reentrance into the 1/3 supersolid above the 1/2 plateau.

cond-mat.str-el↗

arXiv2006

Universal Scaling Behavior of Anomalous Hall Effect and Anomalous Nernst Effect in Itinerant Ferromagnets

Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in a variety of ferromagnetic metals including pure metals, oxides, and chalcogenides, are studied to obtain unified understandings of their origins. We show a universal scaling behavior of anomalous Hall conductivity $σ_{xy}$ as a function of longitudinal conductivity $σ_{xx}$ over five orders of magnitude, which is well explained by a recent theory of the AHE taking into account both the intrinsic and extrinsic contributions. ANE is closely related with AHE and provides us with further information about the low-temperature electronic state of itinerant ferromagnets. Temperature dependence of transverse Peltier coefficient $α_{xy}$ shows an almost similar behavior among various ferromagnets, and this behavior is in good agreement quantitatively with that expected from the Mott rule.

cond-mat.mtrl-sci↗

arXiv2006

Ferroelectric polarization flop in a frustrated magnet MnWO$_4$ induced by magnetic fields

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO$_4$ with long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of ferroelectric phase. An electric polarization flop from the b direction to the a direction has been observed when a magnetic field above 10T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth f-moments.

cond-mat.str-el↗