S. L. Blank

Switching and modulation of light in magneto‐optic waveguides of garnet films

We report for the first time switching and modulation of light in a magneto‐optic waveguide that is a single‐crystal epitaxially grown iron‐garnet film. These experiments involve the Faraday rotation of the magnetic film and the motion of magnetization in the plane of the film. We have modulated light from a 1.152‐μm laser up to 80 MHz. We were also able to switch light between two waveguide modes by applying a magnetic field as small as 0.2 Oe.

Optical waveguides of single‐crystal garnet films

We report light‐wave propagation experiments in single‐crystal epitaxially grown garnet films. The discussion includes refractive index and lattice constant considerations for various garnets, and also the use of iron garnet films on gallium garnet substrates as magneto‐optical waveguides useful in integrated optics.

Magneto‐optics and motion of the magnetization in a film‐waveguide optical switch

We discuss magnetic properties of iron‐garnet films and the use of these films as film‐waveguide optical switches. Our experimental study involves the observation of magnetic domains, measurements of Faraday rotation constants, coercive forces and anisotropy fields, and a detailed investigation of the switching process between 0 and 300 MHz. Our theoretical study includes magneto‐optics in film waveguides, and analysis of the serpentine circuit, and an extensive calculation of the motion of the magnetization. For low driving fields, the process of optical switching is the formation of periodic domains and the subsequent motion of domain walls. For higher driving fields, the process is rotation of the magnetization in unison. The switching field required for 100% modulation is several times the anisotropy field in the film, which can be as small as 0.1 Oe.

Semileaky thin‐film optical isolator

Two interesting effects have been experimentally demonstrated for the first time: (1) simultaneous reciprocal and nonreciprocal mode conversion to achieve an isolation effect and (2) magneto‐optic switching between guided and radiation modes. These effects were observed in connection with the construction of a previously proposed thin‐film optical isolator. The isolator consists of a piece of LiNbO3 placed on top of a thin film of yttrium ion garnet (YIG) with a selenium layer to avoid optical contact problems. The isolator, which is 1 cm long, exhibited 10 dB of isolation at λ = 1.15 μm. The observed isolation was better than theoretical predictions and a mysterious isolation direction dependence on mode order was observed. Although the device had 10 dB of insertion loss and required a magnetic field of 40 Oe, with a slight change in wavelength and film composition, it should be possible to reduce the insertion loss and field required to under 1 dB and 0.1 Oe, respectively. These characteristics combined...

Rapid oxygen diffusion in Ca‐doped yttrium iron garnet films at 25 to 250 °C

Unexpectedly rapid oxygen diffusion has been observed at 25–250 °C in YIG films with uncompensated Ca additions of 0.1 to 0.23 atoms per formula unit. A 3‐μm‐thick film originally dark and conducting due to Fe4+ lightened and became insulating in 15 min at 100 °C in a reducing saturated solution of FeCl2. A diffusion distance of ∼0.5 mm has been observed along a film in 25 h at 250 °C. A model is proposed based on the dependence of the diffusion coefficient D on oxygen vacancy concentration. A magnetic bubble garnet film containing Ca, which also lightened at 250 °C, showed no observable changes in the pertinent bubble parameters.

Three garnet compositions for bubble domain memories

The choice of magnetic garnet compositions for bubble memories is always a compromise dictated by the material requirements generated by the specifications on the memories. The three compositions reported, Y2.62Smo.38Fe3.85Ga1.15O12, Gd2.lLuO.9Fe4.4Al0.6O12, and Yl.92Sm0.1Ca0.98Fe4.02Ge0.98O12, represent three examples of such a compromise. The first composition is excellent for use in circuits operating at 100 KHz over a temperature range of -20° to 80°C. The second has a mobility up to 5000 cm/sec/0e and is capable of very high speed operation at the sacrifice of stability toward temperature. The third exhibits excellent stability toward temperature and has operated at 1 MHz but is compositionally more complex.Melt compositions for film growth and a summary of magnetic properties are presented for the three compositions. Factors to be weighed in composition selection for bubble domain memories are discussed.

Implantability of small bubble diameter garnet films

Measurements of anisotropy in implanted bubble films indicate that in addition to straining the lattice, implantation also has the effect of suppressing the growth‐induced anisotropy. After annealing at 1000 °C, most of the as‐grown anisotropy is restored, which points to oxygen defects as the most likely mechanism for the effect. The Curie temperature has been found to be lowered by as much as 70 °C by implantation at a typical device dose, and the anisotropy of the implanted layer varies quite rapidly with temperature at elevated temperatures. The results indicate that with proper choice of material parameters and implantation conditions safisfactory bubble propagation can be obtained in high density small bubble diameter devices based on ion‐implanted propagation patterns over a wide temperature range.

Velocity of domain walls in an epitaxial yttrium‐europium garnet film

Measurements of magnetic domain velocity by domain transport methods in an epitaxial Y2.4Eu0.6Ga1.2Fe3.8O12 film have yielded values as high as 2800 cm/sec with no sign of saturation. These measurements conflict with those reported recently by Callen et al., who deduced a saturation velocity of 1300 cm/sec from bubble collapse measurements made on films of the same composition. It is suggested that the discrepancy is due to the wall velocity reaching momentarily the Walker breakdown velocity in the bubble collapse technique, which then leads to a relatively immobile spin configuration similar to the one reported recently for hard magnetic bubbles.

Design and development of single‐layer, ion‐implantable small bubble materials for magnetic bubble devices

The general magnetic and physical requirements that a material must meet in order to be useful in magnetic bubble devices are reviewed. An approximate expression relating stripe width and film thickness to the material length parameter (l) is presented. The well‐known equations relating anisotropy, moment, Q factor and exchange constant are rearranged, and, combined with the approximate expression for l, result in a convenient set of equations which are useful for materials design and for evaluating magnetic property measurements. The exchange constant (A) of epitaxial bubble garnet films is presented as a function of Curie temperature. Nominal compositions are given in the (YLuSmCa)3(FeGe)5O12 system which will support bubble diameters from 3.0–1.7μm. The range of λ111 values which are needed to implement Ion Implanted Propagation Patterns (I2P2) is presented. An approach is presented for increasing the uniaxial anisotropy in the 〈111〉 crystallographic direction without significantly changing the damping...

New high−speed bubble garnets based on large gyromagnetic ratios (high g)

A new approach to overcoming the problem of dynamic conversion in high−mobility bubble garnets is described based on large gyromagnetic ratios (high g factors). In a film of Eu1.45Y0.45Ca1.1Fe3.9Si0.6Ge0.5O1 2, a g factor greater than 30 has been obtained, which increases the usable domain wall velocity before onset of dynamic conversion by more than an order of magnitude over comparable bubble garnet films with g approximately 2. Using a circuit period of 28.8 μm, propagation data showing no deterioration in bias margins out to 107 steps were obtained on this film at 1 and 2 MHz.