D. J. Breed

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

Garnet compositions for submicron bubbles with low damping constants

Thin single crystalline films of composition (BiYLu)3(FeGa)5O12 have been grown by liquid phase epitaxy on 〈111〉 substrates with zero lattice mismatch. Optimisation of the Bi:Y:Lu ratio has lead to a 1 μm bubble film on Gd3Ga5O12 (Q = 3.6, 4 πM = 600 gauss and FMRΔH at 10 GHz = 2.8 Oe) and a 0.8 μm bubble film on Sm3Ga5O12 (Q = 2.7, 4 πM = 930 gauss and ΔH = 4.3 Oe). The dynamic coercive fields for these films was <1 Oe. Smaller bubble diameters seem to be feasible in this system. From ferrimagnetic resonance linewidth measurements at 10 GHz it appears that the damping constants in these films are only two times as high as in pure YIG. To increase the damping small concentrations of Sm have been added. For 3 μm bubble films a study of the correlation between the damping constants calculated from the FMR linwidths and the damping constants calculated from the bubble mobilities measured by a translation technique has been made. The agreement between these constants in these films was excellent.

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.

Garnet films for micron and submicron magnetic bubbles with low damping constants

Two types of films for small bubbles have been grown without making use of the rare earth ions which are the cause of increased damping of the Bloch wall motion in the usual small bubble film compositions. Firstly, Bi-containing films were grown on (111) orientated GGG for 1 μm bubbles and secondly, Mn3+-containing films were grown under compression on (100) orientated GGG substrates for 0.4 μm bubbles. The damping constants in these films have been obtained by measuring the FMR line width. The correlation between the damping of the FMR and of the Bloch wall motion is determined in films with bubble diameters of, 2 to 4 μm. The damping constants are a factor 10 to 100 smaller than in the existing device films for small bubbles.

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.

Domain‐wall dynamics in garnet films with orthorhombic anisotropy

The dynamics of domain walls in (110) oriented manganese containing garnet films have been studied. Bubble films and special films in which a single straight domain wall can be stabilized have been prepared. The magnetic anisotropy in these films is orthorhombic and the influence of the in‐plane anisotropy field on the maximum domain‐wall velocity has been studied. The observed maximum velocities, varying between 40 and 1500 m s−1, are usually considerably lower than the maximum velocities predicted by theory. However, for very high in‐plane anisotropy fields the experimental maximum velocities approximate the theoretical ones. From the comparison of different samples it has been concluded that the maximum velocity of the bubbles having no Bloch lines is not very different from the maximum velocity of straight domain walls. Furthermore, it has been shown that the maximum velocity is independent of the film thickness. The influence of external in‐plane fields on the maximum velocity also has been studied. ...

Low damping (BiYLu)3Fe5O12 films with 0.5 μm bubbles

Garnet films of composition (BiYLu)3Fe5O12 have been grown on 〈111〉 Gd3Ga5O12, Sm3Ga5O12, and Nd3Ga5O12 substrates by liquid phase epitaxy. The larger lattice parameter substrates were used in order to increase the bismuth concentration in the films. The anisotropy Ku and the saturation magnetization 4πMs data are presented as a function of the Y/Lu ratio in the melt. The maximum anisotropy obtained was 1.5×105 erg cm−3 which is sufficient to support 0.5‐μm‐diameter bubbles. The ferromagnetic resonance linewidth at 10.1 GHz was measured to be less than 3 Oe. This allows for a domain wall mobility of 600 ms−1Oe−1 in a 0.5 μm bubble film.

Fast wall motion in garnet films with orthorhombic anisotropy

High wall and bubble velocities have been observed in garnet films having a strong orthorhombic anisotropy. This anisotropy is induced by compressive misfit stress in garnets containing Mn3+ ions. The magnetostatics of bubbles in these orthorhombic materials differs from that in uniaxial materials, e.g., no hard bubbles have been observed for large in‐plane anisotropies. Under certain conditions automotion of bubbles has been observed indicating that vertical Bloch lines may be present. Wall mobilities of 55 m s−1Oe−1 and velocities up to 1400 m s−1 have been observed. The possibilities for small bubble diameter applications will be shown.

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.