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We report an experimental demonstration of the magnetoelectric coupling based caloric effect (MCCE) in multiferroic GdFeO3, where the magnetism and ferroelectric polarization are controllable by an external electric field. The temperature of the magnetic material changes when an external electric field is suddenly changed. The temperature dependence of MCCE in a constant magnetic field exhibits a peak below the ordering temperature of Gd moments, where the spin-driven ferroelectricity sets in. The peak temperature is modified with the external magnetic field. Energy-dissipation due to Joule heating in MCCE is expected to be small. The observed MCCE shows a higher energy efficiency than typical magnetocaloric effects and adiabatic nuclear demagnetization at similar temperatures. The present findings provide a proof of concept of MCCE in multiferroics. [ABSTRACT FROM AUTHOR]

It has been well-recognized by the studies on multiferroics in the past two decades that the spin system can produce electric dipoles through the inverse effect of the Dzyaloshinskii--Moriya (DM) interaction. Such an effect combines magnetism and electricity in materials and sometimes leads to ferroelectricity of magnetic origin. In this article, we review multiferroics and skyrmion host materials in which the DM interaction contributes to their magnetoelectric couplings. We classify these materials in terms of magnetic structure and present typical examples of the phenomena related to the DM interaction including the nonlinear magnetoelectric (ME) effect, the control of weak ferromagnetism by an electric field or uniaxial stress, dynamical ME effect, and the formation of magnetic skyrmions. [ABSTRACT FROM AUTHOR]

We have investigated the magnetization process of Bi0.5Ca0.5MnO3 under ultrahigh magnetic fields. The metamagnetic transition due to the magnetic field-induced charge order melting has been observed. The metamagnetic transition becomes broad and smeared in the field ascending process at low temperatures. However, in the field descending process, a clear metamagnetic transition is observed even at low temperatures. Gradual charge order melting by magnetic field, and its reformation are expected to occur in ascending and descending magnetic fields, respectively. Quenched spatial inhomogeneity of the charge distribution and/or quantum criticality can account for the observed asymmetric broadening of the field induced charge order melting. [ABSTRACT FROM AUTHOR]

Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe2 by using Knight-shift measurements for a magnetic field H along all three crystalline axes. In the higher-quality sample, the SC transition temperature Tc is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with Tc ~ 1.6K when H = a and c. Although the Knight-shift behavior was not so different from the previous results for H = b, and c, a large reduction in Knight shift along the a axis was observed, in contrast with the previous a-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results. [ABSTRACT FROM AUTHOR]

To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe2, we measured the NMR Knight shift K and the nuclear spin–lattice relaxation rate 1/T1 in H || a by 125Te-NMR on a 125Te-enriched single-crystal sample. 1/T1T in H || a is much smaller than 1/T1T in H || b and c, and magnetic fluctuations along each axis are derived from the 1/T1T measured in H parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed. The character of magnetic fluctuations in UTe2 is discussed with the comparison to its static susceptibility and the results on other U-based superconductors. It is considered that the magnetic fluctuations probed with the NMR measurements are determined by the magnetic properties inside the two-leg ladder formed by U atoms, which are dominated by the qa = 0 ferromagnetic fluctuations. [ABSTRACT FROM AUTHOR]

We investigate the physical properties of a single crystal of uranium telluride U7Te12. We have confirmed that U7Te12 crystallizes in the hexagonal structure with three nonequivalent crystallographic uranium sites. The paramagnetic moments are estimated to be approximately 1 μB per the uranium site, assuming a uniform moment on all the sites. A ferromagnetic phase transition occurs at TC = 48 K, where the in-plane magnetization increases sharply, whereas the out-of-plane component does not increase significantly. With decreasing temperature further below TC under field-cooling conditions, the out-of-plane component increases rapidly around \(T^{ \star } = 26\) K. In contrast, the in-plane component hardly changes at \(T^{ \star }\). Specific heat measurement indicates no λ-type anomaly around \(T^{ \star }\) , so this is a cross-over suggesting a reorientation of the ordering moments or successive magnetic ordering on the part of the multiple uranium sites. [ABSTRACT FROM AUTHOR]

We investigate the magnetoelectric property of a quasi-two-dimensional magnet Ba2FeSi2O7. An in-plane magnetic field induces a phase transition that is accompanied by only a small magnetization anomaly but apparent electric polarization change. Our numerical simulation using a mean-field Hamiltonian reveals that the transition is associated with a change in the magnetic wave vector from k = (1 0 1/2) to (1 0 0), which originates from the competition between the intralayer Dzyaloshinskii–Moriya (DM) interaction and the interlayer antiferromagnetic exchange interaction. We determine the sign of the DM interaction from the magnetoelectric behavior in the k = (1 0 0) state. We find that the sign of the DM interaction is opposite to that in the case of Ba2CoGe2O7, which is another well-studied isostructural multiferroic material belonging to the melilite family of compounds. [ABSTRACT FROM AUTHOR]

The two-dimensional Heisenberg antiferromagnet (C2H5NH3)2CuCl4 has attracted attention as a good candidate for a type I multiferroic compound. In contrast to magnetism, however, the mechanism of ferroelectricity has not been fully elucidated. The major problems are that ferroelastic 90° domains are readily generated by small external forces and water in the crystal may cause dielectric anomalies. In this study, we observed the changes in the structural and dielectric properties in each domain using birefringence imaging with different temperatures. Furthermore, we have clarified the arrangements of the distorted CuCl6 octahedra using the angular dependences of g-values obtained from electron paramagnetic resonance (EPR) spectroscopy. Birefringence imaging is relatively insensitive to dielectric anomalies, while EPR spectroscopy is sensitive to them. Using the complementary nature of these methods, we have observed the previously reported structural phase transition at 232 K (≡ T3) and have proposed successful new structural models below T3. As for the ferroelectric phase transition, we find no anomalies at around 247 K (≡ T5). However, a birefringence anomaly indicating a ferroelectric phase transition appears at 25.8 K (≡ T6), and the appearance of a small spontaneous polarization is suggested below T6. [ABSTRACT FROM AUTHOR]

The link between the metamagnetic transition and novel spin-triplet superconductivity of UTe2 was discussed thermodynamically through magnetostriction measurements in a pulsed-magnetic field. We revealed a discontinuous magnetostriction across the metamagnetic transition at μ0Hm ≈ 35 T for the applied magnetic fields along the crystallographic b axis in the orthorhombic structure. The resultant volume magnetostriction of ΔV/V ≈ −5.9 × 10-4 gives the initial pressure dependence of Hm by employing the Clausius–Clapeyron's equation, which agrees with previous pressure experiments. Further, significant anisotropic magnetostriction (AMS), derived by subtracting the averaged linear magnetostriction, was revealed. Contrary to the weakly field-dependent AMS along the a axis, those along the b and c axes show strong field dependences with a similar magnitude but with opposite signs, indicating its lattice instability. The relationship between characteristic energy scales of magnetic fields and temperatures was discussed in terms of the Grüneisen parameters compared to the other f-electron systems. The volume shrinkage in UTe2 at Hm, contrary to the volume expansion in typical heavy fermion metamagnets, pushes to invoke the link with the valence instability related to the itinerant-localized dual nature of the U magnetism. [ABSTRACT FROM AUTHOR]

The magnetism of AlxFe2−xGeO5 from x = 0.09 to 0.91 with the andalusite structure was examined. AlxFe2−xGeO5 at low temperatures was found to show a weak ferromagnet-like behavior for x < 0.3 and a spin glass behavior for x > 0.3. The small spontaneous magnetization observed in the weak ferromagnet-like samples may be caused by the existence of Dzyaloshinsky–Moriya interaction and the difference in the magnitudes of the magnetic moments of Fe3+ in the octahedral and trigonal bipyramidal sites. The appearance of the spin glass behavior implies that the dilution of Fe ions by Al ions in AlxFe2−xGeO5 causes the competition between ferromagnetic and antiferromagnetic interactions. The x dependence of the site occupancy of Fe ions suggests that Fe2GeO5 with the andalusite structure cannot be synthesized. [ABSTRACT FROM AUTHOR]

This study investigates the spin susceptibility in U-based superconductor UTe2 in the superconducting (SC) state by using Knight shift measurements for a magnetic field H along the a axis, which is the magnetic easy axis of UTe2. Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature Tc, the a-axis Knight shift in the SC state shows no significant decrease, following the extrapolation from the normal-state temperature dependence. This indicates that the spin susceptibility is nearly unchanged below Tc. Considering the previous Knight shift results for \(H\parallel b\) and \(H\parallel c\) , the dominant SC state is determined to be B3u in the spin-triplet pairing, which is consistent with the spin anisotropy in the normal state. The present result shows that UTe2 is a spin-triplet superconductor with spin degrees of freedom. [ABSTRACT FROM AUTHOR]

We performed ultrasonic measurements on (Ta0.952V0.048)2NiSe5 to investigate the contribution of acoustic phonons at the zone center to structural and possible excitonic transitions. The transverse elastic constant C55 with irreducible representation B2g exhibits softening over 90% above a transition temperature of Ts = 280 K, indicating the soft mode of corresponding TA phonons. Our analysis based on the quadrupole response indicates that the electron–phonon interaction contributes to the excitonic transition in addition to the hybridization between the conduction and valence bands if the excitonic transition is realized. [ABSTRACT FROM AUTHOR]

125Te NMR experiments in field (H) applied along the easy magnetization axis (the a-axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe2. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 30–40 K, where the spin susceptibility along the hard magnetization axis (the b-axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in H || a. We suggest that UTe2 would be located on the paramagnetic side near an electronic phase boundary, where either magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations. [ABSTRACT FROM AUTHOR]

In this study, the metamagnetic transitions in the novel spin-triplet superconductor UTe2 are investigated based on the recently developed simultaneous measurements of magnetization and sample temperature for the applied field along the orthorhombic b-axis and close to the [011] direction, where reentrant superconductivity (RSC) is detected below and above the first-order metamagnetic transition field Hm. Combining Maxwell's relation and the Clausius–Clapeyron equation, we obtain the field dependence of the Sommerfeld coefficient γ through the first-order metamagnetic transition. A significant enhancement in the effective mass toward Hm is detected in both field directions. In contrast, above Hm, the effective mass discontinuously decreases for H || b, while it discontinuously increases for H || ∼[011], which plays a crucial role in the RSC. [ABSTRACT FROM AUTHOR]

We have successfully synthesized a uranium intermetallic compound U2Pt6Ga15 via the gallium flux method. The crystal structure, magnetization, specific heat, and resistivity are investigated. U2Pt6Ga15 is found to crystallize in the hexagonal Sc0.6Fe2Si4.9-type structure with the lattice parameters a = 4.3038(5) and c = 16.297(2) Å. U2Pt6Ga15 is an antiferromagnet with the transition temperature TN = 25.8 K. The enhanced electronic specific heat coefficient γ = 0.1 J=K² U-mol, the coefficient for T² -term of the electrical resistivity at low temperature A = 0.085 µΩ cm=K2, and logarithmic temperature dependence of resistivity characterize this compound as a moderately heavy-fermion system [ABSTRACT FROM AUTHOR]

UTe2 is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe2, we have performed 125Te-NMR measurements, which are sensitive to the local spin susceptibility at a nuclear site. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature Tc in H || b, and a slight decrease in the Knight shift along the b and c axes (Kb and Kc, respectively) below Tc at a low magnetic field H. Although the decrease in Kc vanished above 5.5 T, the decrease in Kb was independent of H up to 6.5 T. To clarify the origin of the shoulder signal and the trace of the decrease in Kb, we compared the 125Te-NMR spectra obtained when H || b and H || c and measured the 125Te-NMR spectra for H || b up to 14.5 T. The intensity of the shoulder signal observed for H || b has a maximum at ∼6 T and vanishes above 10 T, although the superconductivity is confirmed by the χAC measurements, which can survive up to 14.5 T (maximum H in the present measurement). Moreover, the decrease in Kb in the SC state starts to be small around 7 T and almost zero at 12.5 T. This indicates that the SC spin state gradually changes with the application of H. Meanwhile, in H || c, an unexpected broadening without the shoulder signals was observed below Tc at 1 T, and this broadening was quickly suppressed with increasing H. We construct the H–T phase diagram for H || b and H || c based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom. [ABSTRACT FROM AUTHOR]

The high-field multifrequency electron spin resonance (ESR), the magnetization, and the specific heat of single crystals of BaCo2V2O8 (a quasi-one-dimensional Ising-like antiferromagnet with S = 1/2) were measured in two different transverse magnetic fields: H || [100] and H || [110]. A softening of the lowest ESR mode was observed near the saturation field of the magnetization around 40 T in H || [110], whereas it occurs around 10 T in H || [100], far below the saturation field. These observations were reproduced by numerical calculations using the density-matrix renormalization group methods, including the staggered magnetic fields induced by a uniform external magnetic field and the interchain magnetic exchange interaction. We found that the directional dependence of the lowest mode originates mainly from the remarkable angular dependence of the induced magnetic field. The interchain interaction is also quantitatively important for reproducing the experimental results. The directional dependence of the lowest mode is demonstrated by the particle–hole excitation of spinons using the Jordan–Wigner transformation. [ABSTRACT FROM AUTHOR]