Field-induced phase transition in Fe3BO6

The temperature dependence of the field-induced phase transition in Fe₃BO₆ has been measured in fields up to 14.7 T. The experimental value for the anisotropy is compared with the calculated result for the dipole-dipole energy.     

Field-induced magnetic transition in CrCo3

The action of a magnetic field on a single crystal of the compound ErCo₃ has been investigated by both magnetization and neutron diffraction measurements. ErCo₃ is ferrimagnetic with an easy magnetization axis parallel to the c axis of the crystal. When the field is applied perpendicular to the c axis a transition occurs: the moment of one of the two Er sites remains nearly oriented along the c axis while this of the other Er site rotates through an angle of 55°. From the value of the threshold field, the difference between the anisotropy energies of the two sites has been evaluated.     

Field-induced metal-insulator transition in a two-dimensional organic superconductor

The quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3 (Tc approximately 4.4 K) shows very strong Shubnikov-de Haas (SdH) oscillations which are superimposed on a highly anomalous steady background magnetoresistance, Rb. Comparison with de Haas-van Alphen oscillations allows a reliable estimate of Rb which is crucial for the correct extraction of the SdH signal. At low temperatures and high magnetic fields insulating behavior evolves. The magnetoresistance data violate Kohler's rule, i.e., cannot be described within the framework of semiclassical transport theory, but converge onto a universal curve appropriate for dynamical scaling at a metal-insulator transition.     

Field-induced magnetic transition in a Cu-Mn spin-glass alloy

The time-independent magnetization of a Cu-Mn alloy (9 at% Mn) as an isothermal function of field is found to describe an S-shaped curve indicative of a field-induced transition. The critical field for the transition decreases to zero as the temperature is raised to that of the susceptibility cusp.     

Field-induced paramagnons at the metamagnetic transition of Ca1.8Sr0.2RuO4

The magnetic excitations in Ca1.8Sr0.2RuO4 were studied across the metamagnetic transition and as a function of temperature using inelastic neutron scattering. At low temperature and low magnetic field the magnetic response is dominated by a complex superposition of incommensurate antiferromagnetic fluctuations. Upon increasing the magnetic field across the metamagnetic transition, paramagnon and finally well-defined magnon scattering is induced, partially suppressing the incommensurate signals. The high-field phase in Ca1.8Sr0.2RuO4, therefore, has to be considered as an intrinsically ferromagnetic state stabilized by the magnetic field.     

Field-induced structural aging in glasses at ultralow temperatures

In nonequilibrium experiments on the glasses Mylar and BK7, we measured the excess dielectric response after the temporary application of a strong electric bias field at millikelvin temperatures. A model recently developed describes the observed long time decays qualitatively for Mylar [Phys. Rev. Lett. 90, 105501(2003)]], but fails for BK7. In contrast, our results on both samples can be described by including an additional mechanism to the mentioned model with temperature independent decay times of the excess dielectric response. As the origin of this novel process beyond the "tunneling model" we suggest bias field induced structural rearrangements of "tunneling states" that decay by quantum mechanical tunneling.     

Field-induced uniaxial anisotropy in partially ordered Ni3Mn at low temperatures

A uniaxial anisotropy is induced in partially ordered MnNi alloys in the composition range near Ni₃Mn, by applying a magnetic field during cooling from room temperature to 77 K. The uniaxial anisotropy constant K_u depends on both the magnitude of the torque measuring field and that of the cooling field. The easy axis direction tends to be between the 〈100〉 and the direction of the cooling field. The value of K_u shows a maximum when the cooling field is applied along 〈100〉, amounting to 2 × 10⁴ crg/cm³. On the other hand, the crystalline anisotropy is not affected by field cooling. When the temperature is raised from 77 K to 300 K, neither K_u nor the rotational hysterisis loss is observed to have any critical temperature, for a torque measuring field of 20 kOe. As atomic ordering proceeds, these effects become smaller and appear to vanish in the perfectly ordered state.     

Field-induced generation-recombination noise in (100) n-channel Si-MOSFET's at T = 4.2 K: II. Experiments

The spectral noise intensity of the drain current of an n-channel (100) Si-MOSFET in strong inversion was measured as a function of drain current and gate voltage at T = 4.2 K. In addition to flicker noise and white noise it was possible to distinguish a Lorentzian, which was due to generation-recombination noise. Since, at T = 4.2 K, the 2D-electron gas in the MOSFET in strong inversion is degenerate this generation-recombination noise must be caused by traps in the conduction band. The measured noise relaxation time was found to depend on drain current.Our results can be interpreted in terms of a generation-recombination process in which the generation is partly field-induced. Agreement between theory and experiment is within the experimental error, both for the way in which the inverse noise relaxation time depends on drain current and the way in which the ratio of the low frequency plateau of the spectral noise intensity to the noise relaxation time depends on the product of drain current and drain voltage. Measurements of the ratio of the low-frequency plateau of the spectral noise intensity to the relaxation time versus gate voltage at T = 4.2 K we used to construct an energy spectrum of the density of traps in the conduction band. A maximum is observed at about 14meV above the bottom of the conduction band.     

Field-induced giant static dielectric constant in nano-particle aggregates at room temperature

The analogy between magnetism and electricity was established by Maxwell in the 19th century, despite the subtle difference. While magnetic materials display paramagnetism, ferromagnetism, antiferromagnetism and diamagnetism, only paraelectricity, ferroelectricity and antiferrolelectricity have been found in dielectric materials. The missing ‘diaelectricity’ may be found if there exists a material that has a dc-polarization opposing the electric field or a negative dielectric susceptibility ?′???1, with ?′ being the real part of the relative dielectric constant. Both of these properties have been observed in nano-particle aggregates under a dc electric bias field at room temperature. A possible collective effect in the nano-particle aggregates is proposed to account for the observation. ‘Diaelectricity’ implies overscreening by polarization to the external charges. Materials with a negative static ?′ are expected to provide attraction to similar charges and unusual scattering to electromagnetic waves with possible profound implications for high temperature superconductivity and communications.     

Field-induced CDW in HMTSF-TCNQ

Field-induced successive transitions were observed in magnetoresistance in the quasi-one-dimensional organic conductor, HMTSF-TCNQ, hexamethylene-tetraselena-fulvalene-tetracyanoquinodimethane. The magnetoresistance exhibits kink transitions accompanying hysteresis at pressures around 1 GPa, but neither at p=0 nor at 2 GPa. At p=0 and below 30 K, this material undergoes charge density wave (CDW) state, which is suppressed around 1 GPa, where successive transitions are observed. Since these behavior is only observed at the boundary in pressure between insulator and metal, and the nature of the insulating state is CDW at p=0, it is strongly suggested that the successive transitions observed in magnetoresistance might be associated with CDW, accordingly a field-induced CDW by the one-dimensionalization by strong magnetic field ranging from 10 to 30 T. The behaviors are compared with previously claimed FICDW and the established FISDW (field-induced-spin-density-wave).     

Field-induced dispersion in subdiffusion

We discuss the response of continuous-time random walks to an oscillating external field within the generalized master equation approach. We concentrate on the time dependence of the two first moments of the walker's displacement. We show that for power-law waiting-time distributions with 0相似文献   

Field-induced transition on a triangular plane in the spin-ice compound Dy2Ti2O7

The origin of the lowest-temperature anomaly reported several years ago using a polycrystalline sample of the spin-ice compound Dy2Ti2O7 has remained unresolved. Here we finally clarify its origin by susceptibility measurements down to 65 mK using single crystals under accurate control of the magnetic fields in two independent directions. We demonstrate that the transition is induced under a subtle field combination that precisely cancels the nearest-neighbor spin interactions acting on the spins on the triangular lattice within the pyrochlore structure. Contrary to the other two field-induced transitions, this transition is driven only by the interactions beyond the nearest neighbors. Our observation thus provides the first qualitative evidence for the essential importance of the dipolar interaction beyond the nearest neighbors in the spin ice.