Modification of atomic energy levels by two rotating rf fields

The modification of the energy levels for spin-$\text{1}\text{2}$ system by two rotating rf fields is described.     

Surface oxidation kinetics of sputtering targets

Films of compounds can be deposited by sputtering a metal or alloy target in an atmosphere containing a suitable reactive gas. Both Al and 90 : 10 In : Sn targets have been sputtered in argon/oxygen mixtures to obtain Al₂O₃ and indium tin oxide films. The experiments were carried out in a planar magnetron sputtering system with both dc and rf excitation. To investigate the kinetics of the reactive sputtering process, the time dependence of the total gas pressure was measured after a change in oxygen flow rate or sputtering power; a capacitance manometer gave accurate and reproducible results. There were simultaneous changes in the rf matching conditions when rf excitation was used. These changes can be attributed to the formation of an oxide on the target surface. The time dependence of the oxygen pressure measured for the Al and In : Sn targets have been used to compare various models of the reactive sputtering process. Fitting of the experimental values to these models yields values of the equilibrium oxide thickness on the target and these have been compared with measured values. For rf sputtering of an Al target at 500 W with flow rates of $\text{3}\text{ml}\text{min}$ and $\text{2.2}\text{ml}\text{min}$ for argon and oxygen respectively, both the calculated and the measured value of the oxide thickness is 100 nm.     

Quasiquadrupolar echoes in solids containing spins-12 triads undergoing hindered reorientation

The spin echo responses to resonant 90⁰-τ-β_φ⁰ rf pulse sequences in solids containing spin-$\text{1}\text{2}$ triads undergoing hindered rotations, are shown to be predicted by a model of dipolar coupled quasiparticles of spin-$\text{3}\text{2}$.     

Observation of magnetization reversals during relaxation measurements on superfluid 3HeA

A reversal of the recovery of the magnetization following an rf pulse has been observed in superfluid ³HeA in 306 Oe. The time difference between the end of the rf pulse and the start of the magnetization reversal is found to be proportional to both (1 ? T/T_c)^{?$\text{1}\text{2}$} and the magnitude of the initial rotation angle θ.     

Hyperfine structure of 127I2 and 129I2 optical absorption lines

The hyperfine structure of ¹²⁷I₂ and ¹²⁹I₂ rovibronic absorption lines was investigated using either laser induced fluorescence of a collimated molecular beam or saturated absorption in a cell. From the measurements a value for the quadrupole moment ratio ${}^{129}\text{Q}{}^{127}\text{Q}\text{=}\text{0.699}$ is deduced, in good agreement with the result obtained from pure quadrupole spectra in the rf range.     

Neutron diffraction study of UAs in high magnetic fields

Magnetization experiments have shown that at low temperature and in an applied magnetic field of ～90 kOe antiferromagnetic (AF) uranium arsenide transforms to a new ferrimagnetic state. The high-field transition produces a state with magnetic components $\text{parallel}$ to the applied field. A small ferromagnetic component (0.4 μ_B) is seen in magnetization experiments but with neutron diffraction we have observed directly the large AF component (～ 1.8 μ_B) which has a $\text{q}$ value of 0.58 ± 0.01 $\text{c}$¹ in contrast to the zero field type IA structure with $\text{q}\text{= (0,0,0.50)}$. This transition is quite different from that occuring in the conventional spin-flop transition.     

Manifest chiral symmetry preservation in the 1N-expanded SU(N) Thirring model

By utilizing manifestly chiral-invariant auxiliary field operators, it is demonstrated that continuous chiral symmetry is preserved explicitly in the $\text{1}\text{N}$ expansion of 2-dimensional theories whose fermions have a Gross-Neveu type of potential. The effective lagrangian derived in the $\text{1}\text{N}$ limit describes a massless scalar field whose derivative coupling to the fermions vanishes as N → ∞, and a decoupled massive scalar field.     

Approaches to the gravitational spin-32 axial anomaly

The $\text{spin}\text{-}\text{3}\text{2}$ axial anomaly is discussed from various points of view. Two consistent theories for a $\text{spin}\text{-}\text{3}\text{2}$ field interacting with gravity are considered: supergravity and a real quantized $\text{spin}\text{-}\text{3}\text{2}$ field in a classical gravitational background. The Feynman graph method, the zeta function regularization method, the point splitting method and the topological method all yield the same result for the latter theory, in agreement with that first found by Christensen and Duff.     

Magnetoelastic effects in dilute magnetic alloys

Ultrasonic studies of $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Au}$Fe alloys where the concentrations of the transition metal ranges between 1 and 10% show that the longitudinal sound velocity has a marked field dependence at temperatures below the peak in the magnetic susceptibility and a negligible field dependence above it. This suggests that there may be an ordered magnetic state in these alloys.     

Effect of magnetic field on heat flow in a polyatomic gas in intermediate pressure range

The effect of a magnetic field, B, on heat flow in a gas in an intermediate pressure range has been studied. The ratio of the heat flow changes in the fields $\text{B}\text{⊥ ?T}$ and $\text{B}\text{6 ?T}$ was found to change nonmonotonically with pressure in N₂ and CO. With the decreasing pressure, a difference is observed between the dependence of heat flow on field orientation and the corresponding angular dependence in the limiting case Kn→0 ($\text{Kn}\text{=}\text{l}\text{/L}$, $\text{l}$ is the mean free path, L is the geometric size). An expression has been obtained for the heat flow in a magnetic field for Kn ? 0.1 from the solution of an integral kinetic equation. In particular, it has been shown that the special features of the Senftleben-Beenakker effect observed with the decreasing pressure arise not only due to spherically symmetric molecule-surface interaction, but also to nonspherical scattering on walls.     

Quantum theory of longitudinal dielectric response properties of a two-dimensional plasma in a magnetic field

An analysis of dynamic and nonlocal longitudinal dielectric response properties of a two-dimensional Landau-quantized plasma is carried out, using a thermodynamic Green's function formulation of the RPA with a two-dimensional thermal Green's function for electron propagation in a magnetic field developed in closed form. The longitudinal-electrostatic plasmon dispersion relation is discussed in the low wavenumber regime with nonlocal corrections, and Bernstein mode structure is studied for arbitrary wavenumber. All regimes of magnetic field strength and statistics are investigated. The class of integrals treated here should have broad applicability in other two-dimensional and finite slab plasma studies.The two-dimensional static shielding law in a magnetic field is analyzed for low wavenumber, and for large distances we find $\text{V(}\text{r}\text{) ～}\text{Q}\text{k}{}_0{}^2\text{r}{}^3$. The inverse screening length $\text{k}{}_0\text{=}\text{2πe}{}^2\text{??}\text{?ξ}$ (? = density, ξ = chemical potential) is evaluated in all regimes of magnetic field strength and all statistical regimes. k₀ exhibits violent DHVA oscillatory behavior in the degenerate zero-temperature case at higher field strengths, and the shielding is complete when $\text{ξ = r′}\text{l}\text{z.shtsls;}\text{ω}$, but there is no shielding when $\text{ξ ≠ r′}\text{l}\text{z.shtsls;}\text{ω}{}_{\mathrm{c}}$. A careful analysis confirms that there is no shielding at large distances in the degenerate quantum strong field limit $\text{l}\text{z.shtsls;}\text{ω}{}_{\mathrm{c}}\text{> ξ}$. Since shielding does persist in the nondegenerate quantum strong field limit $\text{l}\text{z.shtsls;}\text{ω}{}_{\mathrm{c}}\text{> KT}$, there should be a pronounced change in physical properties that depend on shielding if the system is driven through a high field statistical transition. (It should be noted that the static shielding law of semiclassical and classical models has no dependence on magnetic field in two dimensions, as in three dimensions.) Finally, we find that the zero field two-dimensional Freidel-Kohn “wiggle” static shielding phenomenon is destroyed by the dispersal of the zero field continuum of electron states into the discrete set of Landau-quantized orbitals due to the imposition of the magnetic field.     

Phase diagram of spin-S Ising model in a random magnetic field

A spin-S Ising model with a random magnetic field is studied in the mean field approximation. It is shown that there is no long-range-order, for any value of S, for the value of the fields $\text{h}\text{SJz}\text{? 0.5}$. Complete phase diagrams are constructed numerically for $\text{S = 1}\text{and}\text{S =}\text{3}\text{2}$.     

Electrical resistance and magnetoresistance of amorphous alloys Gd67Co33 and Pd80Si20

In search for structural contributions to the low temperature anomaly we report high resolution resistance and magnetoresistance measurements ($\text{0.02}\text{K}\text{? T ? 20}\text{K}$) of amorphous splats of Gd₆₇Co₃₃ and Pd₈₀Si₂₀. For both alloys, the resistivity ?(H = 0, T) has a minimum at T ～ 10 K and increases with decreasing T. The ferromagnetic Gd₆₇Co₃₃ shows a strong negative field dependence of $\text{Δ?}\text{?(0)}$, saturating at H ～ 2T for T = 4.2 K but no measurable change in $\text{??}\text{?}\text{T}$ below 10 K is observed.The diamagnetic Pd₈₀Si₂₀ exhibits a positive field dependent magnetoresistance $\text{[Δ?}\text{?(0)]}\text{(}\text{H}\text{)}$ at low temperatures. Additionally, a field dependent part in $\text{??}\text{?}\text{T}$ is found which is probably due to paramagnetic impurities (～ 1 ppm Fe). However, there is also a field independent contribution in the amorphous state of Pd₈₀Si₂₀, which vanishes after crystallization. We attribute this to non-magnetic scattering induced by the disordered structure.     

Particle loss from an electron cyclotron resonance discharge plasma in the WT-2 device

The dominant particle loss from an electron cyclotron resonance discharge plasma in a simple toroidal configuration is ascribed to the $\text{E}\text{×}\text{B}$ drift due to the vertical electric field produced by the electrons' toroidal drift. The electron density is increased by adding a small vertical field. This is explained by the electron flow along the line of force canceling the toroidal drift, resulting in reduction of the $\text{E}\text{×}\text{B}$ drift.     

Remanent magnetisation properties of the spin glass phase

We have made a systematic survey of the field and temperature dependence ofthe remanent magnetisation of the spin-glass system $\text{Ag}$Mn in the concentration range 1 to 24%. We parametrise this ensemble of data by the linear field dependence of the thermoremanent magnetisation (TRM), the quadratic field dependence of the isothermal remanent magnetisation (IRM), and by the saturation value of the remanent magnetisation in high field. This enables us to search for a universal behaviour of these parameters in reduced units of temperature and field. We show that at various temperatures the ensemble of reduced curves corresponding to a given concentration alloy are not identical. However, we show that this behaviour is the same at all concentrations, i.e. the field dependence of IRM and TRM depend only on T/T_g. We further show that this dependence is not affected by factors such as the time of measurement, the presence or absence of short-range order or the strength of the amisotropy energy in the system. A suitable parametrisation of this temperature dependence, which we take as exponential, allow us to compare different spin glass systems. We show that the same conclusions appear to hold in $\text{Cu}$Mn, $\text{Au}$Fe, $\text{Pt}$Mn and $\text{La}$Al₂Gd from which we obtain almost the same exponential coefficients. These facts strongly suggest that the mechanism responsible for the existence of a remanent magnetisation exclusively involves exchange interactions and is a general property of the spin-glass phase.     

Crystal field effects in superconducting tunneling

A comparison of the tunnel curves of superconducting $\text{La}$Pr, $\text{La}$Y and $\text{La}$Gd reveals that the character of the tunneling density of states of $\text{La}$Pr is between that of the BCS- and that of the Abrikosov-Gorkov theory. This is expected on theoretical grounds for pair-breaking caused by ions in a singlet ground state. The predicted crystal field induced structures in the tunnel curves could not be detected.     

Stripe domain statics in garnet films

Magnetic garnet films grown epitaxially on nonmagnetic garnet substrates exhibit a growth or stress-induced uniaxial anisotropy in addition to the cubic magnetocrystalline anisotropy associated with their crystal symmetry. When the uniaxial anisotropy is dominant over the cubic, such films exhibit stripe or bubble domain structures; even a small cubic anisotropy component can have a decisive effect on the behavior of the domains in applied fields. We report an experimental study of the quadistatic behavior of domains in fields applied to a (111) film in the film plane along (11$\text{2}$) and ($\text{1}$10). The experimental results are interpreted by a new theory that gives good agreement with the observed behavior, and yields an accurate measurement of the cubic and uniaxial anisotropy constants.The main qualitative features of the results are: In a ($\text{1}$10) field, the walls are Neél walls perpendicular to the field. In a (11$\text{2}$) field the walls are Bloch walls parallel to the field, the domain magnetization in adjacent stripes is not symmetrical about the film plane, and adjacent stripes are not of equal width; the domain period first shrinks and then expands with increasing field; and even though the applied field has no component perpendicular to the film plane, the film develops a net perpendicular magnetic moment.     

Spin-12 particles in the field of monopoles

The equations of motion of a $\text{spin}\text{-}\text{1}\text{2}$ particle in the field of a point-like (Abelian and non-Abelian) monopole are solved; helicity states and scattering solutions are constructed. The motion in an extended monopole and dyon source is discussed: charge-exchange scattering amplitudes are computed in the distorted-wave Born approximation. By the introduction of suitable spinors, the separation of variables is accomplished for any value of isospin. The non-existence of fermion zero modes in the field of an SU(2) monopole when $\text{T > 1, J >}\text{1}\text{2}$ is shown.     

Resonance magnetic field shift induced by electric field for the +12→-12 transition relativistic approach

The resonance magnetic field shift induced by an electric field for the $\text{+}\text{1}\text{2}\text{→-}\text{1}\text{2}$ transition has been interpreted using a relativistic spin motion equation. Two examples are reported.