Range Of External Magnetic Fields Research Articles

Critical scattering of electromagnetic waves on spin fluctuations in nonsaturated magnetic films under acoustic pump

The theoretical and experimental investigation of the microwave (MW) combination scattering on spin fluctuations (SF) in the yttrium iron garnet film under acoustic pump were pursued. MW frequency f≂3.5–4.1 GHz was well above spin wave spectrum at a preassigned magnetic field. At the external magnetic field range H0≂5–40 Oe one (or more) intensity peaks of MW scattering were observed. The positions of these peaks do not depend on MW and surface acoustic wave (SAW) amplitudes and frequencies and depend heavily on the magnetic field directions in a film plane. Because these phenomena were closely associated with the domain walls (DW) reorientation or at the domain structure transformations, e.g., at the flexural instability of DW, one may speculate that critical scattering of MW on SAW and SF was observed. Cross section for such scattering was calculated. In nonsaturated magnetic films the phenomena of MW scattering on SAW and spin fluctuations at high amplitudes of the MW and SAW were investigated as well. In the area of external magnetic fields H0≥250 Oe a stepped dependence of intensity of scattering MW was observed. There is no appropriate explanation of this effect now.

Scaling law for quench energies of composite superconductors

The variation of the quench energy Ec (the minimum heat pulse energy required to destroy the superconductivity) of a composite superconductor with transport current is studied experimentally. The values of Ec for different types of composite are measured in a wide range of external magnetic fields B and transport currents I under different cooling conditions. It is shown that the values of Ec(I, B) satisfy a certain scaling law. This law allows one to put in order a large number of experimental data concerning the quench energy and to simplify the procedure of revealing the quench energy dependence on various parameters. A theoretical approach to interpretation of the scaling law is proposed. The results obtained may be of importance in the study of composite superconductor stability against thermal disturbances.

Magnetic behaviour of Co impurity in dilute PtFe alloys: a nuclear orientation study

Behaviour of the Co magnetic moments in dilute PtFe alloys was studied in the temperature range of 5-50 mK and the external magnetic field range of 0-8.5 T using low-temperature nuclear orientation. Kondo behaviour of Co, known to exist in pure Pt, was found in the sample of lowest concentration only (Pt+0.22 at.% Fe). Large misalignment of the Co magnetic moments was seen, especially for alloys having Fe concentration slightly above the percolation limit 0.76 at.%. An anomaly in the hyperfine field value on the Co nucleus was also found in these alloys.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Noncollinearity of Mn spin in ferromagneticPtFe alloy: a nuclear orientation study

The low-temperature nuclear orientation of54Mn in ferromagnetic Pt+5 at% Fe has been studied in the temperature range 4–50 mK andin the external magnetic field range 0.5–8.5 T. A considerable noncollinearity of Mn magnetic moments with respect to the bulk magnetization direction has been found in the wholeBext range. A model based on the Heisenberg Hamiltonian in the first neighbour approximation is proposed, which fully describes our experimental data.

Magnetic behaviour of Tb impurities in Gd andY single crystals: a nuclear orientation study

The low temperature nuclear orientation of160Tb impurities in Gd andY single crystals has been studied in the temperature range 7–40 mK andin the external magnetic field range 0–7.3 T applied alonga-, b- andc-crystal axes. In the case of Tb in Gd we found a considerable noncollinearity of the Tb magnetic moment with respect to the magnetic external field direction even for highBext. In the case of Tb in Y the results cannot be described by a simple model, taking into account the simultaneous influence of the crystal andexternal magnetic fields. Some new proposals for interpretation of the experimental dat are given.

Antiferromagnetic coupling between the Mn and Fe nearest neighbours in ferromagnetic Mn:Pt-10 at.% Fe

The low-temperature nuclear orientation of 54Mn in ferromagnetic Pt-10 at.% Fe has been studied in the temperature range 4-50 mK and in the external magnetic field range 0.5-8.5 T. Considerable noncollinearity of Mn magnetic moments with respect to the bulk magnetization direction has been found in the whole Bext range. A model based on the Heisenberg Hamiltonian in the first-neighbour approximation is proposed, which fully describes the experimental data. The authors found that the first-neighbor Mn-Fe exchange interaction is antiferromagnetic with the value JMn-Fe=-21(1) K, which lies in the range of the nearest-neighbor Mn-Mn or Fe-Fe exchange interaction parameters for Pt-based alloys.

Magnetization process in high permeability Fe-Cu-Nb-Si-B alloys

The magnetization process has been studied in amorphous Fe 73.5Cu 1Nb 3Si 13.5B 9 alloy before and after fine crystallization by using a very low frequency vibrating sample magnetometer over a wide range of external magnetic field up to 1.8 T. It was found that the H − 1 2 ; term decreases largely after the heat treatment, while the change in the H -1 term was rather small. This fact means that the number of point-like defects was decreased by the heat treatment rather than a change occuring in quasidislocation dipoles.

Unusual magnetic behaviour of Mn spin in magnetic PtFe alloys: Nuclear orientation study

The low temperature nuclear orientation of54Mn in Pt99Fe1, Pt99,9Fe0.1 and Pt99,95Fe0.05 has been studied in the temperature range 5–60 mK and in the external magnetic field range 0–9 T. A considerable noncollinearity of Mn magnetic moments with respect to Bext has been found even at rather high Bext.

Nuclear orientation study of54Mn impurity in Pt100-x Fe x alloy

The low temperature nuclear orientation of54Mn in Pt99.95Fe0.05, Pt99.9Fe0.1, Pt99Fe1 and Pt88Fe12 has been studied in the temperature range 12–50 mK and in the external magnetic field range 0–1.2 T. The strong temperature and external magnetic field dependence of the effective fieldB eff on54Mn has been observed even in the range where the host itself is magnetically saturated. This behaviour is interpreted by noncollinearity of the Mn magnetic moments with respect to the macroscopic magnetisation direction.

Observation of Mn spin canting in PtFe alloys at low temperatures

The low-temperature nuclear orientation of 54Mn in Pt99Fe1 and Pt99.95Fe0.05 has been studied in the temperature range 12-50 mK and in the external magnetic field range 0-1.2 T. The strong temperature and external magnetic field dependence of the effective field Beff on 54Mn has been observed even in the range where the host itself is magnetically saturated. This behaviour is interpreted by noncollinearity of the Mn magnetic moments with respect to the macroscopic magnetisation direction.

Phase diagram for the triangular Ising lattice

A magnetic phase diagram for the triangular Ising lattice with nearest-neighbor and next-nearest-neighbor interactions, both being antiferromagnetic, is calculated within the molecular field approximation. It is shown that there appear several intermediate phases between low-temperature and paramagnetic phases for an appropriate range of external magnetic field.

An extended lattice model of liquid helium four

A description of the low- and high-temperature behavior of liquid He is given in terms of an extended Matsubara-Matsuda lattice model. Paying particular attention to the kinematical interaction and to the hard core of the bosons leads to a unified theory for the low-temperature behavior and for the lambda transition. Since the hard-core boson operators in the lattice model correspond to spin one-half operators, one can interpret the hamiltonian as the hamiltonian of a magnetic system of oblate form, i.e., the x-y coupling is stronger than the z coupling. A rotation introduced in the space of these operators results in a hamiltonian consisting of three parts: one part is of the anisotropic Heisenberg form, the second contains pairs of creation-annihilation operators at different lattice sites and the third part consists of an interaction between creation-annihilation operators and the z component of the spin operators. A particular choice of the rotation angle eliminates the third part. The equations of motion of the creation and annihilation operators are decoupled with the aid of a momentum-dependent Bogoliubov-like transformation. This leads to a linear energy spectrum and a self-consistent integral equation for the magnetization. An approximation of this self-consistency equation provides a temperature dependence of the magnetization and leads to a critical temperature for a range of external magnetic fields. It is found that in the rotated frame the angle of rotation and the magnetization exhibit a jump at the transition temperature. Consequently, the transition is of second order.

Further results on the operation of high-accuracy drift chambers

Optimization of the working parameters in the drift chambers with adjustable electric fields permits stable operation and high accuracies. Full saturation of the drift velocity leads to remarkable improvements, namely a very linear space-time correlation for perpendicular tracks, and simple geometrical distortion of linearity for inclined tracks. The same results can be obtained when properly tilting the electric field equipotentials in a wide range of external magnetic fields. This simple behaviour should allow a practical use, even for large systems, of the intrinsic high accuracy of the drift chambers (100–200 μm). They appear then as a very promising high-resolution fast detector for high-energy particle physics.