Fumihiko Ishida

Submicron bubble garnets and their characterizations

New Submicron ( 0.5-1.0 \mu m diam) bubble garnets have been developed. In order to reduce saturation induction 4\piMs as low as possible, suitable choice of amounts of nonmagnetic ions substituting for ferric ions in both tetrahedral and octahedral sites were studied in (YSm) 3 (FeAl) 5 O 12 , (YSmLu) 3 - (FeGaSc) 5 O 12 , (YSmLu) 3 (FeAlSc) 5 O 12 and (LaLuSm) 3 - (FeGa) 5 O 12 garnet systems. For example, in (YSmLu) 3 - (FeAlSc) 5 O 12 a film with the following properties was grown; strip width w = 0.7\mu m, film thickness h= 0.7\mu m, quality factor q=2.8 , Curie temperature Tc= 140\deg C and 4\piMs=770 G. The temperature properties of those films could be improved drastically by doping with a small amount of Gd ion. Wall mobilities μw of those films are in the region from 200 to 500cm/s/Oe. Preceding these material studies, several film characterization methods have been investigated. Film thickness was measured by Fluorescent X-ray method, strip width by using a highly sensitivity TV camera, and bubble collapse field by FMR resonance technique respectively.

Peak Effect in Superconducting Nb‐15 at.% Zr‐45 at.% Ti Alloys

The H‐Ic characteristics of Nb‐15 at. % Zr‐45 at. % Ti alloys are experimentally discussed in relation to metallurgical structure, particularly, precipitation. Peak effect may be due to the random distribution in barrier heights and the interaction between flux lines at the magnetic fields near Hc2.

Magnetic loss and domain‐wall mobility in magnetic bubble garnet films

Magnetic loss and domain‐wall mobility have been studied in the bubble garnet system (YSmLuCa)3(FeGe)5O12 and in large gyromagnetic ratio (high‐g) garnets such as (LaTmCa)3(FeGe)5O12, (YErCa)3(FeGe)5O12, and (YEuCa)3(FeGeSi)5O12. The resonance line width ΔH increases as the concentration of the rare‐earth ion in the film increases and decreases as the saturation induction 4πMs increases. The product MsΔH depends only on the rare‐earth ion in the film and its concentration. We consider this product as a magnetic loss parameter because it is proportional to the concentration of the rare‐earth ion, which is closely related to the magnetic loss energy of the garnet system. The modified Landau‐Lifshitz damping parameter Λ(≡λ/γ2; λ: normal Landau‐Lifshitz damping parameter; γ: gyromagnetic ratio) is found to be proportional to MsΔH. It is shown that Λ is preferable to the Gilbert damping parameter α and λ itself in studying the dynamic properties such as domain‐wall mobility.

Comparison of Ge substituted and Ga substituted garnet for 1.5 μm diameter bubble devices

A comparison has been made of (YSmLuCa)3(FeGe)5O12 and (YSmLuGd)3(FeGa)5O12 for 1.5 μm diameter bubble devices. The melt composition for film growth, and a summary of magnetic properties, are presented here for each composition. Y1.1Sm0.4Lu0.7Ca0.8Fe4.2Ge0.8O12 has a higher Curie temperature (222°C) and shows a collapse field temperature coefficient (−0.20%/°C) over a wider temperature range (−20 ∼ 80°C). Both materials demonstrate nearly the same saturation induction (530 ∼ 540 G) and wall mobility (410 ∼ 450 cm/sec/Oe) in films with a characteristic length of l = 0.17 μm and an anisotropy field of Hk = 1900 Oe. It seems that (YSmLuCa)3(FeGe)5O12 is more suitable for practical use from the viewpoint of temperature properties.

Distribution coefficients in (YSmLuCa)3(FeGe)5O12 film growth

Abstract The composition of bubble garnet films has been analyzed by Inductively Coupled Plasma Emission Spectroscopy (ICP) to determine the distribution coefficients for different growth conditions. Under typical growth conditions, the distribution coefficients, k, of each element are as follows: kY = 2.15, kSm = 1.56, kLu = 1.32, kCa = 0.45, kFe = 0.98, kGe = 1.10. As the supercooling temperature (growth rate) increases, kCa, which is the smallest and deviates most from 1.0, changes in the direction approaching 1.0. For charge compensation, kGe also increases, consequently, kFe must decrease. Also kY, which is the largest, k Sm k Y and k Lu k Y change in the direction approaching 1.0. On the other hand, as the melt parameter R1 (≡ Fe 2 O 3 Σ Ln 2 O 3 ) increases, kFe decreases, and kY, kSm and kLu increase, whereas k Sm k Y and k Lu k Y remain constant at 0.73 and 0.61, respectively.

Zero temperature coefficient collapse field magnetic bubbles with 1.8-µm diameter

Small diameter (1.8 μm) bubbles with zero temperature coefficients of bubble collapse field H 0 and bubble strip-out field H 2 were obtained in (Y Sm Lu Ca) 3-x Gd x (Fe Ge) 5 O 12 garnets. Doping with a small amount of Gd (x = 0.35) reduces the temperature variation of the saturation induction 4πM s to -0.16 percent/°C. Consequently the variations of H 0 and H 2 are flat in a wide temperature range (-20\deg \sim 100\deg C), while the strip width w changes at the rate of -0.15 percent/°C. The dynamic properties are almost the same as those in the pure case (x = 0). The initial wall mobility μw is 400 cm/s/Oe, and the saturation velocity is 60 m/s. The temperature variation of several properties in films of this system was compared with the temperature variation of those in films of the (Y Sm Lu) 3-x Gd x (Fe Ga) 5 O 12 system. The Ca-Ge substituted system is more suited to supporting bubbles with zero temperature coefficient collapse field.

Submicron magnetic bubble material of (YSmLu)3(FeGaSc)5O12

A new submicron magnetic bubble garnet of (YSmLu)3 (FeGaSc)5O12 with low saturation induction 4πMs if found. By suitable combination of amounts of Ga and Sc, 4πMs can be kept to a practical minimum. The usefulness of substitution for ferric ions in both tetrahedral and octahedral sites by nonmagnetic ions for the reduction of 4πMs in submicron bubble garnets is shown. For example, films with the following properties are grown: stripe domain width w=0.9 μm; characteristic length l=0.10 μm quality factor q=2.6; and 4πMs=600 G.

High g Bubble Garnets Without Containing Eu3+ Ion

New high g (gyromagnetic ratio) garnets for magnetic bubble applications have been found. In (La Tm Ca) 3 (Fe Ge) 5 O 12 films, g becomes larger than 20, and the saturation wall velocity exceeds 1800 m/s. The mechanism of high g s in these garnets can be explained by high magnetic losses of rare earth ions in the garnet. It is concluded that high g garnets can be obtained by using not only Eu 3+ ion but also almost all magnetic rare earth ions except Gd 3+ .

Growth and characterization of Al-substituted iron garnets for submicron diameter bubble films

Abstract Al-substituted rare-earth iron garnet films have been grown that support submicron diameter bubbles. In developing small diameter bubble films, reduction of the saturation induction of a film, 4πMS, is very important because power consumption in drive coils and chip heating increase drastically with higher magnetization. Aluminum ions have been found to be one of the most suitable substitution ions for this purpose. Moreover, owing to the small ionic radius of Al ions, it is easy to meet the lattice matching requirement between films and GGG substrates without lattice adjusting ions such as lutetium. Submicron diameter bubble films are easily grown by the conventional LPE technique in the garnet system (YSmGd) 3 (FeAl) 5 O 12 . They show good bubble properties, well suited to practical use.

Influence of R 1 parameter {=Fe 2 O 3 /(Y 2 O 3 + Sm 2 O 3 + Lu 2 O 3 )} on magnetic bubble properties of (YSmLuCa) 3 (FeGe) 5 O 12

The influence of R 1 {=Fe 2 O 3 /(Y 2 O 3 +Sm 2 O 3 +Lu 2 O 3 )} in the melt composition on film properties, and growth characteristics, has been investigated for (YSmLuCa) 3 (FeGe) 5 O 12 . The garnet phase is the primary phase when R 1 is kept between 10 and 60. The temperature coefficient for the bubble collapse filed changes from -0.29 to -0.19 %/°C, and the growth rate with 10°C supercooling changes from 0.60 to 0.15 μm/min, by increasing R 1 =10 to 60. Distribution coefficients, KY, KSm, KLuand KGeincrease, and KFeand KCadecrease, with increasing R 1 .