Magnetization of uranium monopnictides in fields up to 40 T

Magnetization measurements at 1.3, 20 and 77 K on UN, UP, UAs and USb in fields up to 40 T are reported. While UN and USb have straight magnetization curves, UP and UAs show a number of magnetic transitions with extremely large hysteresis.     

High-field magnetization of giant moment-spin glass PdMn alloys in pulsed fields up to 40 T

Magnetization curves up to 40 T are presented for $\text{Pd}$Mn alloys with Mn concentrations between 0.48 and 9.8 at.%. Estimates for the exchange parameters and saturation moments are obtained, and a comparison with Monte Carlo simulations is made.     

Magnetization measurements and the magnetic inhomogeneity of random metal alloys

It is argued that the straightness or otherwise of plots of M_b² vs (B₀/M_b) (where M_b is the magnetization in a magnetic induction B_o and at approximately zero temperature) for different concentrations in the critical or percolation concentration region for long-range ferromagnetic order in atomically disordered metal alloys is neither a satisfactory measure of the magnetic (and/or metallurgical) homogeneity of the alloys nor is it an acceptable test of the applicability of Landau's theory of phase transitions to such alloy systems.     

Magneto-tunneling spectroscopy of GaAs---AlGaAs double barrier tunneling devices in pulsed high magnetic fields up to 40T

The magneto-tunneling effect was investigated in GaAs---AlGaAs double barrier resonant tunneling devices in pulsed high magnetic fiels up to 40T applied parallel(B) and perpendicular (B) to the barrier layers. In a sample with , oscillatory structures due to the 2D electrons in the emitter and the LO phonon assisted resonant tunneling were observed when the magnetic field (B) was swept at constant bias voltages. A large drop of the current was found in the quantum limit at applied voltages below the negative differential conductivity region. A striking hysteresis was observed in the voltage-current (V - I) curves. In a wide well sample with , rich structures were observed in the V - I curve for B, corresponding to the tunneling to different cyclotron orbits from the emitter.     

Magnetization measurements of polycrystal ZnMn alloys at very low temperatures

The magnetization of ZnMn alloys with Mn concentration ranging from 68 to 1 ppm has been measured from 2 K down to 10 mK. The results show large departures from free spin behavior due to impurity-impurity interactions and some concentration independent effects.     

Spin-flip Raman laser at magnetic fields up to 14 T

We extended the range of operation of the CO₂ laser pumped spin-flip Raman laser in n-InSb up to magnetic fields of 14 T. The laser at high fields is strongly influenced by optical phonons which interact resonantly with the electron spin system, and by intraband absorption of the Raman scattered light in the scattering medium.     

Semiconductor-metal transition in FeSi in ultrahigh magnetic fields up to 450 T

The magnetic susceptibility and conductivity of single-crystal iron monosilicide are investigated in ultrahigh magnetic fields up to 450 T at a temperature of 77 K. It is found that the conductivity of iron monosilicide increases continuously by two orders of magnitude as the magnetic field increases. The results obtained can be interpreted as a semiconductor-metal transition induced by the magnetic field. The dependence of the conductivity on the magnetic field is described well on the basis of the spin-fluctuation theory. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 326–330 (25 August 1998)     

NMR study of re-entrant spin-glass state in NiMn alloys

The temperature dependence of the average hyperfine field H̄_i and the nuclear spin-lattice relaxation time T₁ of ⁵⁵Mn on three different types (i = I, II and III) of Mn atoms in NiMn alloys containing 10 and 15 at % Mn have been measured. In 15 at % Mn alloy, H̄_III associated with Mn atoms having an antiparallel moment μ_III increases abruptly at 12K, while H̄_I and H̄_II associated with Mn atoms having parallel moments μ_I and μ_II do not with decreasing temperature. On the other hand T⁻¹₁ of ⁵⁵Mn of all three types of Mn atoms are largely enhanced at the same temperature, 12 K. This behavior was not observed in 10 at % Mn alloy.These effects observed in 15 at % Mn alloy are considered to be due to the freezing of the transverse component of the antiparallel moment μ_III due to the onset of the re-entrant spin-glass transition at 12 K.     

Investigation of the spin-glass state in γ-Fe-Ni-Mn alloys

The composition region where there are no long-range ferro- and antiferromagnetic order has been determined in γ-Fe-Ni-Mn alloys. In these alloys strong small-angle magnetic neutron scattering has been obtained. The intensity has an unusual temperature dependence which is discussed in the framework of the critical neutron scattering thermodynamic theory. The ground state of these alloys is identified with the spin-glass state in which there are also regions of both short-range ferro- and antiferromagnetic order.     

Magnetization and magnetic aftereffect in textured Ni/Cu compositionally-modulated alloys

The magnetic properties of Ni/Cu compositionally-modulated alloys with [100], [110] and [111] textures were measured by magnetometry and ferromagnetic resonance. These alloys were found to exhibit a pronounced magnetic aftereffect.     

Shubnikov-de Haas oscillations in n-channel silicon 〈100〉 MOSFETS in magnetic fields up to 35 T

Shubnikov-de Haas oscillations have been studied in n-channel silicon 〈100〉 MOSFETS in magnetic fields up to 35 T. At high magnetic fields the shape of the conductivity peaks becomes asymmetric and the conductivity from whole regions of the Landau level spectrum is suppressed by the magnetic field. The asymmetry is thought to arise from the low effective density of scatterers which occurs for high magnetic fields, as predicted by Ando. These effects may also be related to the presence of phenomena such as Wigner crystallisation or Anderson localisation.     

Magnetospectroscopy of double HgTe/CdHgTe QWs with inverted band structure in high magnetic fields up to 30 T

Magnetoabsorption in far and mid IR ranges in double HgTe/CdHgTe quantum wells with inverted band structure has been studied in high magnetic fields up to 30 T. Numerous intraband and interband transitions have been revealed in the spectra and interpreted within axial 8 × 8 k·p model. Splitting of dominant magnetoabsorption lines resulting from optical transitions from hole-like zero-mode Landau level has been discovered and discussed in terms of a built-in electric field and collective phenomena.     

Doppler-free two-photon absorption spectroscopy of trans-glyoxal under magnetic fields up to 6T

In order to measure the Doppler-free two-photon absorption (DFTPA) spectrum in the presence of a strong magnetic field, a sample cell placed in an optical resonator was installed at the centre of the bore of a superconducting magnet capable of generating a magnetic field of up to 6T. Changes in spectra of the A ¹A_u ← X ¹A_g transition of trans-glyoxal were measured as a function of magnetic field strength. Level crossings induced by Zeeman energy shifts were observed. The perturbing level, which shows hyperfine splitting, was identified as the ³A_u(nπ?) state, because the hyperfine splitting is small in the ³B_u(^ππ?) state and large in the ³A_u(nπ?) state. The perturbation between the A ¹A_u(nπ?) and ³A_u(nπ?) states was shown to take place by either vibronic interaction or Zeeman interaction between the ³A_u(nπ?) state and the ³B_u(ππ?) component mixed to the A ¹A_u(nπ?) state by spin-orbit interaction. The magnetic moment of the A ¹A_u state was determined to be approximately 0.0028μ_B, and the magnitude of the mixing coefficients 〈1 ³B_u|H _so|1 ¹A_u〉/[E(1 ¹A_u) ? E(1 ³B_u)] was evaluated to be 0.026.     

Magnetic correlation,excitation and slow dynamics in concentrated spin-glass alloys

Three kinds of neutron scattering experiments have been performed to clarify the role of magnetic clusters on the various properties of re-entrant spin-glasses. The presence of two kinds of spin-wave excitations, the limitations of magnetic phase diagrams and the mechanism of slow dynamics have been discussed based on the results of inelastic scattering, diffuse scattering and time-resolved small-angle scattering experiments, respectively.     

Probing the anisotropy constants of SmCo5 and PrCo5 by Hall resistance measurements in pulsed high magnetic fields up to 47 T

In order to assess the anisotropy constants of highly anisotropic thin film samples with anisotropy fields well above 10 T, Hall resistance measurements were conducted in pulsed magnetic fields. These measurements also deliver the anomalous Hall data, which are proportional to the perpendicular magnetisation. This specific approach combines the high field values obtainable by pulsed fields with a measurement technique sensitive enough to be applied to thin film samples. Two epitaxial Rare Earth-Cobalt thin films with large in-plane uniaxial magnetocrystalline anisotropy at room temperature were studied. The resulting anisotropy fields and constants are discussed with respect to measurements on single crystals and similar films investigated in quasi-static magnetic fields well below the anisotropy field. The present technique proved to be very valuable to highly anisotropic samples, as the approach to saturation is fully monitored and the data thus provides a more extended view on the hard axis magnetisation process.     

A SQUID susceptometer for fields up to 8.5 tesla

A SQUID susceptometer working in fields up to 8.5 T has been built. Calibration measurements show a mass susceptibility sensitivity of 6.3 10⁻¹³ m³·kg⁻¹ (for a one gram sample) and an excellent reproducibility. The temperature of the samples can be changed from 1.6 to 300 K by a regulated continuous He flow. System design, strategy for minimizing the sources of noise and measurement techniques are described. A test measurement showing the martensitic transition of V₃Si in 8.5 T is presented.