摘要:

The structure of a two‐dimensional 180° Bloch‐type domain wall in a ferromagnetic film has been generated directly from an iterative micromagnetic energy minimization. The resultant magnetization distribution (which varies through the thickness of the film as well as in the plane of the film perpendicular to the wall) is observed to be significantly different from previous one‐dimensional models. The equilibrium wall structure is characterized by extensive flux closure internal to the film, very low pole densities on the film surfaces, asymmetry in the magnetization distribution perpendicular to the wall, and an approximately linear dependence of the over‐all wall width on film thickness. Finally, it is found that the total wall energy in this two‐dimensional model is less than one‐half the comparable value predicted from the most accurate one‐dimensional treatment for 1000 Å Permalloy films and less than one‐third the corresponding one‐dimensional value at 2000 Å.

ISSN:0021-8979    

DOI:10.1063/1.1658014

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

We calculate the threshold values of applied magnetic field for magnetization reversal or domain formation in uniaxial ferromagnets. The calculation is carried out for ellipsoidal specimens whose dimensions are large compared with typical domain dimensions. The threshold curve reduces to the familiar astroid for thin films whose plane contains the easy axis.

ISSN:0021-8979    

DOI:10.1063/1.1658015

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In this paper it is demonstrated that the anisotropy, as measured by Hiraokaet al., in the extraordinary Hall constantR1of nickel can be theoretically predicted but cannot be explained in terms of the anisotropy in the resistivity alone. A quantum calculation, using both the tight‐binding approximation and the Karplus‐Luttinger theory of the extraordinary Hall effect, is performed to show the existence and estimate the magnitude of the anisotropy inR1. The phenomenological equations for the anisotropy in the resistivity, as derived by Do¨ring, are employed to indicate that Hiraoka's experimental results cannot be explained only in terms of the anisotropy in the resistivity measured in the direction of the Hall voltage.

ISSN:0021-8979    

DOI:10.1063/1.1658016

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Substituted CdCr2S4spinels containing Ni, Co, V, and Ti were prepared for magnetic study. Substitution of In3+for Cd2+was used for charge compensation when divalent transition‐metal ions were substituted for Cr3+. In the spinels Cd0.8In0.2[Cr1.8Ni0.2]S4, Cd0.8In0.2[Cr1.8Co0.2]S4and Cd0.8In0.2[Co0.2Cr1.8]Se4the Ni2+and Co2+were both found (by magnetic measurements) to interact negatively (antiferromagnetically) with the Cr3+ion. The V3+and Ti3+ions in CdV0.2Cr1.8S4and CdTi0.2Cr1.8S4appear to have no magnetic moment. The measured magnetic moments of these spinels are in excellent agreement with theoretical values based only on the moment of Cr3+. In the compound Cd0.8In0.2[Cr1.8V0.2]S4the measurements indicated that the V2+ion is not stable with respect to the Cr2+ion. The resulting ionic distribution would be Cd0.8In0.2[V0.23+Cr0.22+Cr1.63+]S4instead of Cd0.8In0.2[V0.22+Cr1.83+] S4. Two additional compositions containing 0.1 and 0.3 mole of vanadium exhibited magnetic moments which are consistent with the formation of V3+and Cr2+.

ISSN:0021-8979    

DOI:10.1063/1.1658017

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Sequences of photographs with 10 &mgr; resolution have been taken during high‐speed flux reversal and as the magnetization relaxes upon termination of the drive field. Equipment used consisted of a sampling Kerr magneto‐optic camera with aQ‐switched ruby laser for a light source. The 10 nsec exposure time was synchronized with a variable time delay between application of the magnetic field and actuation of the camera stable to within 3 nsec. The results show that, with zero transverse field, longitudinal propagation of diffuse transverse boundaries and nucleation of partially reversed regions are processes that are involved in intermediate and high‐speed switching, respectively. The velocity of the diffuse boundary varies approximately as H5, and the mobility is as large as 1.4 cm/Oe·&mgr;sec. With a transverse field, the low‐speed reversal is similar to diffuse boundary propagation and the higher‐speed processes are rotational in nature. The transition from propagational to rotational phenomenon is abrupt. Blocking is easily observable. If the reversing field is terminated prior to saturation, the flux either continues to reverse or relaxes to a less switched condition, in times of the order of 1 &mgr;sec, casting considerable doubt on conclusions drawn from interrupted pulse experiments.

ISSN:0021-8979    

DOI:10.1063/1.1658018

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The magnetoresistance of a conducting solid has been measured at high frequencies through the techniques of microwave spectroscopy. The measurement is based on the detection of electromagnetic power absorbed by conduction electrons under the conditions imposed by a resonant cavity and an external magnetic field. The magnetic field dependence of this power absorption is calculated and verified experimentally within one order‐of‐magnitude for a thin copper film. The method developed has potential application to the measurement of mobility of charge carriers in organic substances. In certain biomolecules, particularly those that are important in life processes, mobility measurements should be useful in distinguishing electronic and protonic conduction processes.

ISSN:0021-8979    

DOI:10.1063/1.1658019

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The instability threshold has been derived for transversely pumped magnetoelastic waves in YIG for the case where the equilibrium position of the magnetization vector is in an arbitrary direction with respect to the crystal axes. It is shown that the threshold has a finite value for magnetoelastic waves propagating parallel to the direction of the internal magnetic field and that the threshold is minimum near crossover. It is also shown that the threshold is lowest when the internal field is rotated ∼15° with respect to one of the ⟨100⟩ cubic axes of YIG. The recently developed geometrical ray theory analysis is used to determine the exact propagation path of the magnetoelastic waves in an axially magnetized rod and to compute the magnitude of the angle &thgr; between the wave vectorkand the direction of the internal magnetic field. Results show that the magnetoelastic waves focus about the direction of the field and that &thgr;≅1° or less. The ray theory analysis and the nonlinear theory have been combined, and the threshold has been determined at each point along the ray. The results satisfactorily explain the experimental observations on parametric amplification of magnetoelastic waves in YIG, reported in an earlier paper.

ISSN:0021-8979    

DOI:10.1063/1.1658020

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A simple phenomenological constitutive equation for porous materials is proposed, which allows a detailed description of irreversible compaction behavior at low pressures and reduces to the correct Hugoniot description at high pressures. The theory is compared to some existing data on Hugoniots of porous aluminum and iron, and fairly simple functional forms of the compaction relation are found to be adequate to fit the data. The constitutive relation is suitable for use with finite difference methods of solution of the one‐ and two‐dimensional equations of motion governing stress wave propagation. Examples of such solutions in one dimension are given to illustrate some of the features of the theory.

ISSN:0021-8979    

DOI:10.1063/1.1658021

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A precision torsion pendulum with electronic resetting mechanism is described. Prior to each swing, it is held electromagnetically against a stop where it stays for several seconds, held by an automatic time delay. Upon each release, the rotating disk thus has exactly the same starting potential. After a free rotation of several degrees, a beam of light reflected from a mirror on the disk sweeps over a photocell starting a crystal‐controlled electronic digital counter. The pendulum then continues clockwise to its maximum excursion and reverses. Upon its counterclockwise return motion it stops the counter as the beam of light sweeps over the photocell in the reverse direction. The recorded times are printed out automatically. They are observed with and without concentric weights added to the rotating disk. In adding weights, there are four factors which act to lengthen the period of the pendulum: the increase in the moment of inertia due to the masses of the added weights, the change in dimensions of the suspending wire, the decreased torsional stiffness of this wire, and the energy used in raising and lowering the disk because of the Poynting effect. The latter three depend on the weights added. When account is taken of these four factors, there is excellent agreement between the observed and computed changes in period with the added loads. Proof is thus furnished that the period of a torsion pendulum is weight sensitive.

ISSN:0021-8979    

DOI:10.1063/1.1658022

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An experimental study of the effect of axial tension on the torsional stiffness of circular wires was made under static conditions and well within the elastic limits for both twist and stretch. The method used was to apply a constant couple to the bottom of a vertical wire and to note optically how the angle of twist changed as the tension on the wire was varied. It was carried out with four different alloys. Variations in angle were observed to be related linearly to the applied tensions and to be in excess of those which arise from the change in dimensions, except for one alloy for which the effect is either nonexistent or too small to be detected. In all cases there is an initial residual twist. In general, an increase in axial tension produces a decrease in torsional stiffness, except where the effect of the residual twist is greater than and opposed to this decrease. The results are also shown to be in qualitative agreement with the classical experiments on the Poynting effect, an effect which can be explained by modern second‐order theory of elasticity.

ISSN:0021-8979    

DOI:10.1063/1.1658023

出版商:AIP    

年代:1969

数据来源: AIP