Antonius Bernard Voermans

Increased domain wall velocities due to an orthorhombic anisotropy in garnet epitaxial films

Magnetic domain wall velocities are compared for (Eu,Lu)3 (Fe,Al)5O12 films grown on (110) and (111) Gd3Ga5O12 substrates. The (110) films have an orthorhombic anisotropy which is partly stress induced and partly growth induced; the (111) films are uniaxial. Wall velocities approaching 500 m/sec have been measured in the orthorhombic films while the (111) films exhibit a maximum velocity of ∼5 m/sec. The results are compared with theoretical limiting velocities.

New bubble materials with high peak velocity

Peak velocities higher than 40000 cm s-1and domain wall mobilities of the order of 1500 cm s-1Oe-1were measured by the dynamic bubble collapse method in garnet films having an orthorhombic anisotropy. The orthorhombic anisotropy was realized by growing garnet films with positive magnetostriction constants under strong compression on

Magnetic properties and growth conditions of manganese‐containing iron garnet films for magnetic bubbles

Manganese can be substituted in iron garnet films in order to increase the magnetostriction constants. When these films are grown under compression, magnetic anisotropy is introduced. The influence of manganese on film‐growth conditions and magnetic properties has been studied. Phenomenological equations are derived to describe the properties of the manganese‐containing garnet films. These equations were successfully applied in a test case of tailoring the properties of garnet films.

Fast 1‐ and 2‐μm bubbles in films with orthorhombic anisotropy

In this paper it will be shown that high bubble velocities can be realized in garnet films with orthorhombic anisotropy for 2‐μm as well as for 1‐μm bubbles, if bubbles without Bloch lines have been used. Then the maximum velocity is at least 200 ms−1 for 2‐μm bubbles and 100 ms−1 for 1‐μm bubbles. It appears that bubble diameter and collapse field of these bubbles strongly depend on the value and on the direction of the in‐plane field. Small and large bubbles were observed simultaneously in the presence of in‐plane fields. Much lower velocities and a strong scatter in the velocity data were observed for bubbles with other wall states.

Bubble device materials with orthorhombic anisotropy

The growth characteristics and the magnetic properties of Mn‐substituted garnet films grown on (110) oriented substrates are reported. On perfectly oriented substrates hillocks are observed which occur due to the fact that (110) is a habit face. By the introduction of a slight misorientation of the substrates, the hillocks disappear and the surfaces are perfectly flat. Mn is substituted in the garnet to obtain the right magneto‐elastic properties. It is shown that the temperature dependence of the magnetic parameters can be adjusted such as required to provide a device material.

Decomposition of garnet epitaxial layers caused by annealing

The changes in chemical composition which accompany the process of stress relief in garnet epitaxial layers during annealing have been studied. It is shown that the process involves the evaporation of PbO and formation of Fe2O3 crystals on the layer surface. The associated volume reduction of the garnet layer results in the observed decrease in the lattice‐misfit stress. Weight‐loss measurements with a thermobalance have been employed to monitor the evaporation of PbO, and a quantitative comparison with the amount of Fe2O3 observed by optical microscopy has been made. These results are interpreted in terms of a specific decomposition reaction and are found to be in numerical agreement with x‐ray diffraction measurements of the lattice changes.

High domain‐wall velocities in (Gd,Lu)3(Fe,Mn,Al)5O12 garnet epilayers with orthorhombic anisotropy

Garnet films can be given orthorhombic anisotropy by growing films with positive magnetostriction constants under compression on (110) ‐oriented substrates. The positive magnetostriction is achieved by the incorporation of Mn3+ ions in (Gd,Lu)3Fe5O12 films. In this way bubble films with a strong in‐plane anisotropy field are obtained. This in‐plane anisotropy increases the maximum velocity of the domain walls to at least 40 000 cm s−1. The domain‐wall mobility in these films is about 1500 cm s−1 Oe−1. The dependence of the domain‐wall velocity on the anisotropy and on the orientation of the domain wall in the film plane is shown.

Orthorhombic magnetic anisotropy in garnet epitaxial films containing europium

We have determined the conditions under which an orthorhombic anisotropy can be induced in epitaxial (Eu, Lu)3Fe5O12 films such that the easy axis is normal to the film surface and the medium and hard axes are in plane. The presence of the in‐plane anisotropy has been shown in a previous publication to increase the maximum domain‐wall velocity substantially above that of comparable uniaxial materials. Suitable anisotropies have been found in films grown in compression on (110) Gd3Ga5O12 substrates. The resulting anisotropy is shown to be partly stress induced and partly growth induced; a separation of the two components has been obtained by examining films with different misfit strains and by measuring the anisotropy torques, magnetization, and lattice misfit as a function of temperature. Films grown on (111) and (100) substrates have also been examined. The results indicate that a two‐parameter model of the growth‐induced anisotropy is incapable of describing the magnetic anisotropies measured for the ab...

High frequency propagation of magnetic bubbles in dual conductor devices

Garnet epitaxial films with an orthorhombic anisotropy and a 1.7 μm bubble diameter have been grown under strong compression on 〈110〉 oriented G.G.G. substrates. The bubble mobility in these films is about 60 m/s ⋅ Oe and the maximum velocity is about 50 m/s. Dual conductor circuits with an 8 μm period have been processed onto these films with a planar processing technology. It has been shown that a Poly Tetra Fluoro Ethylene spacer reduces strongly the influence of the mechanical stresses in the overlay on the magnetic properties of the strongly magnetostrictive epi‐layer. This spacer is necessary for good propagation characteristics. At 6 MHz propagation margins of 14% have been observed at a linear current density of 2 mA/μm.

Induced orthorhombic anisotropy in (Eu, Lu)3Fe5O12 epitaxial films

Films of Eu3−xLuxFe5O12 where 0.6 < × <1.4 were grown by liquid phase epitaxy onto (110) Gd3Ga5O12 substrates. The films were found to contain an orthorhombic magnetic anisotropy which was induced both by the growth process and by the stress due to the film-substrate lattice misfit. There is a limited range of misfit (composition) values which result in an easy axis perpendicular to the film surface and a large in-plane anisotropy.