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.     

Oscillations of local magnetization in the semi-infinite antiferromagnet

The presence of the boundary in the semi-infinite antiferromagnetic chain is shown to produce spatial oscillations of the local magnetization. A Green function technique is used to obtain the exact form of these Friedel-type oscillations within the spin $\text{1}\text{2}$XY model. It is shown that a non-zero external magnetic field is the necessary condition for the oscillating behavior of the local magnetization. Comparison is made with an earlier treatment of the infinite chain with a weak perturbation potential     

Non-linear magnetization dynamics of ferromagnetic insulators at parallel pumping

The non-linear dynamic equation for weakly anisotropic ferromagnetic insulators at parallel pumping in the region of frequencies less than that of the parametric resonance is derived. This equation is used for solving some non-linear problems. The process of the non-linear relaxation of magnetization is considered. The non-linear loss in energy in ferromagnets is studied in the low-frequency region ωτ_∥ ? 1, where τ_∥ is the time relaxation of magnetization connected with the dipole-dipole interaction. In the frequency region ωτ_∥ ? 1 a new type of instability is found. If the amplitude of the variable magnetic field $\text{H(t) =}\text{H}\text{+ h}\text{cos}\text{ωτ}$ satisfies the condition $\text{h}\text{H}\text{? Z}{}_{\mathrm{<mtext>c</mtext>}}\text{≈ 2}$, then the ferromagnet is characterized by the stationary homogeneous value of magnetization. In the amplitude region $\text{h/}\text{H > Z}{}_{\mathrm{<mtext>c</mtext>}}$, this state is unstable and the magnetization starts rotating. At the threshold of instability the magnetic state changes abruptly. The loss in energy in the stability region is found.     

Autocorrelation function of the x-component of the magnetization in the one-dimensional XY-model

Exact expressions are derived for the time-dependent correlation functions of the x and y component of the magnetization for the one-dimensional anisotropic XY-model ($\text{S=}\text{1}\text{2}$) in zero field in the high-temperature limit. As a corollary, the correlation functions for the Ising chain in a transverse field are obtained.     

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.     

Crystal field effects in PrAl2

We re-examine the crystal field interpretation of inelastic neutron scattering results on PrAl₂. With the crystal field parameters x = 0.75 and W = 0.315 meV and the molecular field parameter $\text{λ}\text{=}\text{145 kOe}\text{μ}\text{B}$ we can explain the crystal field effects of susceptibility, spontaneous magnetization, specific heat capacity and electrical sensitivity of PrAl₂ rather well.     

Interpretation of Kondo experiments in a magnetic field

Thermodynamical properties of the “resonance level model” are calculated for arbitrary spin and magnetic field. Assuming this model to describe the basic physics of the Kondo problem we find a satisfactory agreement with recent magnetization data on $\text{Ag}$Fe.     

Gauge internal symmetry in extended supergravity

Extended supergravity theories with global O(2) and SO(3) internal symmetry have recently been constructed, and a mechanism which implements local O(2) and SO(3) gauge invariance is given here. The introduction of a minimal gauge coupling automatically leads to a $\text{spin}\text{-}\text{3}\text{2}$ mass and a cosmological term in order to preserve local supersymmetry. Local internal symmetry for a $\text{spin}\text{-}\text{3}\text{2}$ field is related to spontaneous breakdown of global supersymmetry. Perturbation theory results which confirm the physical consistency of the system are given.     

The magnetic field and force in a perpendicularly magnetized matrix consisting of parallel ordered ferromagnetic wires

A formula for the magnetic field arising in a periodically ordered array of ferromagnetic wires, whose magnetization is saturated in a perpendicularly applied field, is derived. Thereby it is assumed that the stray fields do not affect the magnetization of the wires. It is shown that for an arbitrary infinite lattice of wires the exact solution of the magnetostatic equations is given by the Weierstrass $\text{p}$-function and how this function can be used to approximate the field in a finite array of wires. In view of applications to HGMS an expression for the magnetic force acting on a small weakly magnetic particle in a ferromagnetic matrix is derived, which is well-suited for numerical calculations.     

High-field magnetization of PdMn and PdFeMn spin glass-ferromagnetic alloys

We have measured the low-temperature magnetization of $\text{Pd}$Mn (4.0 and 9.8 at% Mn) and $\text{Pd}$FeMn (0.35 at% Fe, 0.5 at% Mn) with fields ? 15T. A different magnetization behaviour is noted between the 9.8 at% spin glass and the alloys with lower Mn-concentrations. The latter show a ferromagnetic character and no irreversibilities or relaxation effects.     

Critical phenomena of ferromagnetic cobalt disulfide

The simultaneous measurements of magnetization and resistivity of a ferromagnetic CoS₂ near the critical temperature have shown that the negative divergence of $\text{d}\text{ρ}\text{d}\text{T}$ occurs exactly at the Curie temperature of 115.9 K. The magnetization satisfies the static scaling law.     

Paramagnetism of gases in the radiation field

The behaviour of paramagnetic gas (alkaly metal vapour) resonantly interacting with monochromatic radiation, in the presence of a longitudinal constant magnetic field is investigated. The method of quasienergy states and the statistic distribution over the sublevels of atomic ground state in the magnetic field are used. The expression for magnetization are derived as a function of constant magnetic field and of electromagnetic field of different polarizations (the nonlinear inverse Faraday effect particularly) for the case of two-level ($\text{j}{}_1\text{=}\text{1}\text{2}\text{→ j}{}_2\text{=}\text{1}\text{2}\text{,}\text{3}\text{2}$ transitions) and the three-level ($\text{j}{}_1\text{=}\text{1}\text{2}\text{→ j}{}_2\text{=}\text{3}\text{2}\text{→ j}{}_3\text{=}\text{1}\text{2}$ transitions, two-photon resonance) atoms. In the case of two-level atoms an interval of electromagnetic field intensity exists for any given magnetic field where the paramagnetic gas becomes diamagnetic. In the case of two-photon resonance magnetic properties of gas does essentially depend on relative sign of one- and two-photon resonance detunings. When these signs coincide, the atom which behaves like the two-level and in the opposite case the magnetization is described by the Langevin-formula.     

Consistency requirements for 1N expandable field theories

It is demonstrated that $\text{1}\text{N}$ expansion in a class of field theories with an internal O(N) symmetry leads to pathologies. Therefore, these models are either not internally consistent, or their perturbation expansions (ordinary as well as $\text{1}\text{N}$ are unreliable.     

Nonlinear response to external magnetic fields

The purpose of this paper is to study conditions under which a system of itinerate spin-$\text{1}\text{2}$ fermions might exhibit a macroscopic linear response to external magnetic fields after long times. Exact expressions are obtained for the nonlinear response of the magnetization and the total energy. We find that for a constant field there is no response (our model contains no mechanism for the relaxation of spins). For an oscillatory field there is a response in which secular terms (in the time) appear which are associated both with nonlinear terms in the external field and with contributions from the background medium. The secular terms involving the magnetic field would not be seen if one used the usual approximations of microscopic linear response theory. They give rise to new conditions which must be satisfied if the system is to exhibit a macroscopic linear response in the long-time limit.     

Anomalous permeability in Polder-Smit region of ferrites

A study of the magneto-microwave Kerr effect on two samples of ferrites lying in the Polder-Smit region gives a negative value of μ', the real part of the transverse diagonal term of permeability tensor. There is a negative peak for μ' at a d.c. magnetization approximately equal to $\text{3}\text{4}$ of the saturation magnetization.     

High field magnetization of europium-graphite intercalation compound C6Eu

The whole magnetization curve of the first stage compound C₆Eu has been measured by using pulsed fields up to 400 kG below 40 K. For H ⊥ c, c being the crystal c-axis, four regions are observed in the magnetization curve; I) the initial magnetization region with an apparent moment of ～ 0.6micro_B per Eu ion (H < 12 kG), II) the intermediate region with nearly constant moment of 2.2 – 2.7 micro_B, which corresponds to $\text{1}\text{3}$ the full moment of Eu²⁺ ion (22 < H < 82 kG), III) the region of a linear field dependence (82 < H < 205 kG), and IV) the saturation region above 205 kG, where the saturation moment is found as 6.2 micro_B. For H//c, the magnetization increases monotonically and approaches to a saturation value corresponding to 6 micro_B above 240 kG.     

The role of magnetic clusters in mictomagnetic alloys

The average moment and the concentration of magnetic clusters in $\text{Cu}$-Mn alloys were determined from magnetization data. Both are increased by aging. Magnetic clusters are responsible for most of both the extremely large steady field susceptibility at 4.2°K after zero-field cooling and the alternating low-field susceptability at its peak.     

Magnetization process and principal magnetic susceptibilities in RbMnF3

The temperature dependence of χ_⊥, initialχ_p (powder), and evaluated χ_∥ for RbMnF₃ are reported for the temperature range of 4.2–106 K. A shallow minimum at $\text{T}\text{T}{}_{\mathrm{N}}\text{? 0.72}$ is observed in χ_⊥. The field dependence of the magnetization shows a smooth rotation of the spins to a normal direction above H_c ? 2.43 kOe at 4.2 K.     

Planar hall effect in gadolinium thin films near the curie point

The orientational and thermal dependences of planar Hall effect in Gd thin films deposited in an ultra-high vacuum were studied between 100 and 300 K. The critical exponent of magnetization as estimated from these measurements is $\text{β =}\text{1}\text{3}$.