Iron Garnet Layers Research Articles

Characterisation of bismuth-doped yttrium iron garnet layers prepared by sol–gel process

Yttrium iron garnets and Bi-substituted yttrium iron garnets were prepared by two different sol–gel processes. We investigated the evolution with temperature of XRD patterns and of the magnetisation of powders issued from sol–gel solution decomposition. We prepared layers on silica glass by the spin- or dip-coating processes. XRD patterns on layers were also obtained. The dependency of the Faraday effect upon the light wavelength and Bi amount was shown. The main result is the possibility to prepare stable sol–gel solutions containing bismuth, yttrium and iron precursors which lead to garnet phase after annealing at low temperature. These bismuth-doped garnet phases give the expected magneto-optical properties. These processes are promising for the preparation of inexpensive magneto-optical recording media.

Magnetically Tunable Microwave Filters based on YBCO/YIG/GGG Heterostructures

Superconducting, monolithic magnetically tunable microwave filters have been designed and fabricated demonstrating high tuning ranges (up to 19%) at a center frequency of 10 GHz. These filters are based on fully epitaxial YBa2Cu3O7 (YBCO) thin films grown by pulsed laser deposition onto liquid-phase epitaxy yttrium iron garnet (YIG) layers on gadolinium iron garnet (GGG) substrates. Mechanisms resulting in variations of the bandwidth and insertion losses upon tuning are analyzed and understood in terms of the material properties of YIG and GGG.

Crystal ion slicing of single-crystal magnetic garnet films

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report here an implementation of epitaxial liftoff in magnetic garnets. Deep ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG (Bi-YIG) epitaxial layers grown on gadolinium gallium garnet (GGG). The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. Ten-micron-thick films have been lifted off from the original GGG substrates by etching in phosphoric acid. Millimeter-size pieces of excellent quality have been transferred to the silicon and gallium arsenide substrates. Study of the magnetic domain structure in the detached epilayers by Faraday contrast shows no changes in film anisotropy. Optical insertion loss measurements are also presented.

Huge Enhancement of the Magneto-Optical Faraday Effect of Films with Disordered Multilayer Structures Supporting the Localization of Light

The magneto-optical (MO) Faraday effect of films with disordered multilayer structures was analyzed theoretically, using the random matrix approach. The films were composed by stacking bismuth-substituted yttrium iron garnet (Bi: YIG) layers and silicon dioxide (SiO2) layers in a disordered sequence. When the multilayer film has a disordered structure appropriate for supporting the lacalization of light, the Faraday rotation angle θF of the film is extraordinarily enlarged: for instance, at λ (wavelength of light) = 1.15 μm, θF increases by more than 6.0deg/μm, which is about 30 times more than the inherent value for the Bi: YIG single film (θF=0.2 deg/μm). This is considered to be a novel mechanism for enhancing the MO Faraday effect, and is very attractive for various MO applications, including optical communication and high-density MO recording.

Stability of Bi containing epitaxial iron garnet layers

The annealing behavior up to 1300°C of Bi containing epitaxial Y- and Gd-iron garnet layers was investigated by X-ray diffraction. Up to 1000°C in situ measurements were performed using a resistance furnace (±2° C). Stability of the layers is demonstrated to decrease with increasing Bi content, when misfits at annealing temperature are comparable. For comparable Bi content stability of those layers decreases with increasing misfit at the annealing temperature.

Dissolution of iron garnet LPE layers in acidic solutions containing reducing agents

The dissolution rates of liquid phase epitaxial iron garnet layers in acidic solvents are increased by up to two orders of magnitude in the presence of suitable reducing agents. Experiments with differently orientated layers and with single crystal spheres reveal a change in the anisotropy of dissolution rates.

The growth of bismuth iron garnet layers by liquid phase epitaxy

A review is given of the liquid phase epitaxial growth of bismuth-substituted iron garnet layers. It covers especially crystal growth aspects: e.g. flux compositions, layer compositions, saturation and growth temperatures, defects, as far as reported in the reviewed literature since the first papers on this topic in 1973. Two sections on substrates and on experimental considerations are followed by a section on phase diagram investigations. The main part is structured according to the flux system used.

LPE growth of bismuth substituted gadolinium iron garnet layers: Systematization of experimental results

Experimental data concerning the solubility behaviour of bismuth, aluminium, gallium substituted gadolinium iron garnet in lead oxide/bismuth oxide based melts as well as the segregation behaviour of the substituents are systematized with the aid of available theoretical models.

Dynamic properties of charged walls in ion implanted garnets

The dynamic behavior of the charged wall in the ion implanted layer of contiguous disk bubble devices is determined for the first time without the disturbing influence of a bubble domain being coupled to the charged wall. The charged wall was stabilized next to a nonimplanted region by an applied in-plane field Hx and was oscillated along ŷ by an rf field hy sin ωt. Oscillations in Faraday magneto-optic contrast signals proportional to the wall oscillations were detected with a high-speed photomultiplier (PMT) when a focused laser beam was obliquely incident on the region of the charged wall. The drive frequency ω was provided by an rf tracking generator which was phase locked to a spectrum analyzer set to detect the fundamental amplitude response of the PMT signals. Our measurements were made on the doped yttrium iron garnet (YIG) layers Gd, Tm, Ga:YIG and Eu, Tm, Ga: YIG typically used for driving 5- and 1-μm bubbles, respectively. The charged wall amplitude rolloff with frequency interpreted in terms of an overdamped linear oscillator reveals a relaxation frequency near 10 MHz when Hx = 30 Oe, for example, in contrast to ∼0.5 MHz when the bubble is attached. The linear mobility of the charged wall μcw = 6600 cm/sec Oe determined in Gd, Tm, Ga: YIG from the relaxation frequency contrasts with an effective mobility μeff = 250 cm/sec Oe when the bubble is attached. These results confirm our earlier assumption [B. E. Argyle, et al., IEEE Trans. MAG-14, 593 (1978)] that the damping which affects the upper limiting frequency of operation in this contiguous disc material comes mainly from the bubble domain and almost none (i.e., ≲5%) from the charged wall. In addition, no velocity saturation effects are observed in the isolated charged wall at least up to 12.8 MHz. The maximum velocity 28 000 cm/sec inferred from the maximum harmonic amplitude at this frequency is at least 25 times the saturation velocity of an isolated bubble, e.g., 1100 cm/sec, in the nonimplanted film. A simple theoretical model taking into account restoring torques on the wall magnetization due to in-plane anisotropy and wall demagnetization predicts velocity saturation will occur at yet several times larger velocity than the maximum response we can observe in the present experiment.

Facet formation of yttrium iron garnet layers grown epitaxially on spheres

The formation of facets of yttrium iron garnet layers with thicknesses of 1 to 8 μm was studied by liquid phase epitaxy using polished spheres of gadolinium gallium garnet single crystals of 2 to 8 mm diameter as substrates. The most dominant (largest area) facets were {110} and {211} which frequently exhibited flat, spiral type growth hillocks. {321} facets were always a little bit smaller. {210} and {332} facets were found to be very small and not completely flat. No facets could be observed in the [100] directions but the surfaces of these layers show a quite different texture compared to other directions such as [111]. The sticking of melt droplets to the [100] directions of the sphere proves the preference of wetting for this direction.

The characterization of magnetic bubble-domain materials with X-ray topography

The use of X-ray topography to characterize magnetic bubble materials is discussed. By mapping the crystal strains, the technique reveals defects which can influence the bubble domains and which are not easily observed by other methods. Examples of topographs are given for flux grown iron garnets, Czochralski grown Gd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> substrate crystals, and LPE iron garnet layers. The influence of substrate defects on the magnetic film is demonstrated. Transmission topographs of substrate-film combinations have not revealed an intermediate layer of misfit dislocations. The application of X-ray topography to a study of the growth induced anisotropy in magnetic garnets is also described. The topographs reveal a correlation between regions having a particular growth band symmetry and those having a particular noncubic anisotropy.