摘要:

Unusual cylindrical magnetic bubble domains completely bounded by domain walls have been stabilized inside YbFe03platelets with high surface coercivities. The energy density of the walls forming the cylinder ends manifests itself as an effective bias field, which, for platelet thicknesses between 55–75&mgr;, stabilizes bubbles in zero applied field. Annealing at 700°C for one hour reduced the coercivity associated with bubble propagation to 0.25 Oe. A theoretical analysis of the stability and coercivity of these self‐biased bubbles is given.

ISSN:0094-243X    

DOI:10.1063/1.3699411

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The existence of stable reversal domains in thin film strips is predicted. The background magnetization is assumed to lie in the plane of the film and to be oriented perpendicular to the strip. Magnetostatic forces, which tend to enlarge a domain, are balanced by a bias field oriented against the magnetization within the domain. The force function is given in the limit in which the film thickness is negligible compared to the other dimensions of the domain. The bias field margins determined by spontaneous nucleation at the low end, and vanishing domain width at the upper end, are estimated.

ISSN:0094-243X    

DOI:10.1063/1.3699412

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The temperature stability of cylindrical domains in a hexagonal array in basal cobalt foils has been investigated theoretically and experimentally. Minimisation of the total energy shows that below a critical value of the anisotropy constant the magnetization begins to tilt from the c‐axis, Lorentz micrographs vindicate this prediction and show that the spin distribution in a bubble changes symmetrically to produce a Bloch line in the centre. It is thought that the results of these experiments indicate possible nucleation mechanisms for bubbles.

ISSN:0094-243X    

DOI:10.1063/1.3699413

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

A rigorous solution of the micromagnetic equations for moving domain walls is presented assuming uniaxial anisotropy and uniform wall velocity. This solution applies for wall velocities smaller than a critical velocityv1 = &ggr;(HaD)1/2 [ (1 + &sgr;)1/2 − 1].Here &ggr; is the gyromagnetic ratio, Hathe anisotropy field, D the exchange constant, &sgr; = 4&pgr;Mo/Ha, and Mothe saturation magnetization. The wall energy E increases with increasing v according to E = Eoa(v), where Eois the energy of the wall at rest, a(v) is proportional to the reciprocal of the wall width, and is given byv2/&ggr;2HaD =  − (1 + &sgr;)a−2 + 2 + &sgr; − a2.At the critical velocity the derivative of the wall energy with respect to v becomes infinite, the wall energy itself remains finite. The “tails” of the domain wall (the regions where the magnetization approaches alignment with the anisotropy axis) can be considered as spin waves of imaginary wavenumber and frequency but real phase velocity. The parameter a in Eq. (2) is (apart from a constant factor) the imaginary part of the wavenumber. The domain velocity v is the same as the phase velocity of these spin waves. The wall mobility is velocity dependent, being inversely proportional to the wall energy in this velocity range. The structure of domain walls moving at speeds exceeding v1is discussed.

ISSN:0094-243X    

DOI:10.1063/1.3699414

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The equation of motion for the bubble domain, in which the position and radius of the bubble are variable, has been formulated and solved under several types of propagating fields. It has been found that the maximum speed of bubble propagation is obtained when the propagating field has the form of a traveling wave. For the traveling wave, four types of bubble motion were derived, that is, (1) collapse of the bubble (2) stretching of the bubble (3) normal propagation with constant speed, and (4) anomalous propagation. In the anomalous propagation the frequency differs from that of the propagating field. Characteristics of the propagating field, the maximum frequency of bubble propagation, and the dynamic properties of bubble domain are discussed.

ISSN:0094-243X    

DOI:10.1063/1.3699415

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Equations of motion for a flexed domain wall are derived. Velocity dependence of wall thickness is neglected. The orientation angle of the wall‐moment is canonically conjugate to the wall position. Walker's uniform‐motion solution is stable. At higher fields, the wall oscillates. A general method of evaluating the non‐linear mobility in the limit of small damping and small field is given.

ISSN:0094-243X    

DOI:10.1063/1.3699416

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Bubble collapse times were determined as a means to characterize wall velocity vs. drive field in thin (3 to 11 &mgr;m) epitaxial garnet films of compositions near Y3Ga1Fe4O12, Eu0.5Y2.5Ga1Fe4O12and Gd0.5Y2.5Ga1Fe4O12. The results resemble that reported for thick platelets ( > 25 &mgr; thick) with large diameter bubbles ( d ≈ 25 &mgr;). An initial steep slope (∼103cm/sec‐oe) is followed by a curve of diminishing slope. The deviation from linearity occurs well below Walker's limit of velocity Vw= 2&pgr;&ggr;Ms▵valid for free wall motion in a plate of infinite thickness. Our theory shows that when damping (Gilbert'sa) is small, stray fields near the film surface destabilize the linear uniform motion. At fields above the limit Hc= 9. 5ax (2&pgr;A)1/2h−1irregular Bloch line motion occurs and the mean wall velocity approaches the asymptoteVo = 7.1 &ggr;Ah−1K1/2To the extent that experimental knee velocities are well defined, they range from 1/2 to 1 times Vo.

ISSN:0094-243X    

DOI:10.1063/1.3699417

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Increased domain wall mobilities have been observed with increased gallium concentration in liquid phase epitaxial (LEE) films of Ga and/or Al substituted Eu3−xErxFe5012. As the total substitution is raised from about 0.7 to 1.8 of the 5 Fe ions, the Neel temperature, YN, decreases from 450 K to 320 K and the mobility rises from ∼25 to ∼450 cm/sec Oe. Reduced uniaxial anisotropy accounts for only a minor part of this increase in mobility. Reduction of the exchange energy by ∼25% in the low Neel temperature samples should give rise to a reduction of ∼13% in their mobilities, opposite to the observed change. Differences in thickness or magnetization between the samples do not correlate with the mobility changes. The coercivity decreases with TN, but this is probably not the cause of the increase in mobility. Variations of the g‐factor from ∼0.6 to >7 were observed in these materials but this increased g probably also does not account for the mobility increases. The relevant mechanisms could include reduced cubic anisotropy or changes of rare‐ earth energy levels and corresponding decreases in the wall damping. In these materials, the improved mobilities are achieved at the expense of inferior temperature sensitivity since the magnetic compensation point is raised above room temperature.

ISSN:0094-243X    

DOI:10.1063/1.3699418

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

A growth‐induced noncubic magnetic anisotropy, similar to that reported for garnets containing a mixture of rare earth ions, has been observed in YIG. It is illustrated by a comparison of X‐ray topographs of the crystal strain with the magnetic domain structure detected optically by means of the local Faraday rotation. Annealing at 1190°C in a nitrogen atmosphere removes the noncubic magnetic anisotropy. The suggested mechanisms involving a pairing or site preference of two or more different magnetic ions are not applicable to these results.

ISSN:0094-243X    

DOI:10.1063/1.3699419

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Mixed rare earth iron garnet crystals often show a growth anisotropy, an orthorhombic contribution to their magneto‐crystalline anisotropy determined by the growth facet from under which the material is taken. We have observed the optical birefringence associated with this anomalous anisotropy. The anisotropy and the birefringence are both found to fall off monotonically with increasing distance from the growth surface. Two other contributions to the observed birefringence are attributable to localized strain and the so called linear magnetic birefringence.

ISSN:0094-243X    

DOI:10.1063/1.3699420

出版商:AIP    

年代:1972

数据来源: AIP