Liquid Phase Epitaxial Garnet Research Articles

Influence of in-plane field on vertical Bloch line in the walls of the second kind of dumbbell domains at various temperatures

The stability of vertical Bloch lines (VBLs) in the second kind of dumbbell domain (IIDs) walls in liquid phase epitaxy garnet bubble films subjected to an in-plane field at various temperatures is studied experimentally. It is found that there exists a critical in-plane field range depending on temperature, in which vertical Bloch lines (VBLs) in the second kind of IIDs walls are unstable, i.e., [Hip(1)(T),Hip(2)(T)]. Here, Hip(1)(T) is the initial critical in-plane field at which VBLs in the walls of IIDs annihilate; while Hip(2)(T) is the lowest in-plane field at which all VBLs in the walls of IIDs have annihilated completely. Also, the critical in-plane field range [Hip(1)(T),Hip(2)(T)],Hip(1)(T) and Hip(2)(T) all decrease with the temperature increasing. Hip(1)(T) and Hip(2)(T) reach zero at T0′ and T0, respectively.

Reducing the optical absorption of LPE garnet films at a wavelength of around 1000 nm

This paper concerns the reduction of optical absorption loss L of Bi-substituted rare-earth iron garnet films at a wavelength of around 1000 nm for use as a 45/spl deg/ Faraday rotator of an optical isolator. First, a single crystal of Nd/sub 1.21/Gd/sub 1.74/Sc/sub 2.07/Ga/sub 2.98/O/sub 12/, with a lattice constant of 1.2619 nm, was grown by the Czochralski method. Using this crystal as a substrate, Nd/sub 1.69/Bi/sub 1.31/Fe/sub 5/O/sub 12/ film was grown by the LPE (Liquid Phase Epitaxial) method. The resultant LPE film showed a reduced optical absorption at around 1000 nm, because its optical absorption peak at around 900 nm due to the Fe/sup 3+/ crystal field transition from /sup 8/A/sub 1g/ to /sup 4/T/sub 1g/ shifted toward short wavelengths. In addition, the LPE film's Faraday rotation coefficient increased, since Nd, as Bi does, contributes negatively to the Faraday rotation. The value of L for the LPE film was found to be 2.6 dB at a wavelength of 980 nm, and 1.0 dB at 1017 nm.

Reduction of optical absorption at a wavelength of around 0.8 ?m in LPE garnet (TmBiCa)3(FeGaPt)5O12

Liquid-phase epitaxy (LPE) garnet films (TmBiCa)3(FeGaPt)5O12 have been grown using only Bi2O3 as the flux so that the film containing Bi gives high specific Faraday rotation. The film does not contain Pb, which may affect optical absorption. The optical absorption coefficientα at 810 nm has been effectively reduced by doping Ca in the melt. Our data show that a minimum level ofα and of the anisotropy constantKu and also the maximum of the electrical resistivityϱ are achieved when Ca2+ replaces Fe2+. Fe2+ results from Pt4+ incorporation in the film due to a Bi2O3 flux attack on a Pt crucible. Using a compensated film,α of 58 cm−1 and a figure of merit of 9deg/dB were obtained.

Flux residule on liquid phase epitaxial Bi-substituted garnet films and wetting between wafers and flux

Flux residue on the surface after liquid phase epitaxial (LPE) growth of garnet films, which is a serious problem particularly for Bi-substituted garnet films, was studied from the viewpoint of wetting between garnet surface and fluxes. Two kinds of experiments were carried out: (i) observation of the flux residue mode on the surface of (LuBi)3Fe5O12 garnet films with various crystallographic orientations and (ii) contact angle measurements for various combinations of garnet wafers and flux compositions. Flux residue took place on the surface of {100} and {111} (LuBi)3Fe5O12 garnet films, where the contact angle was 0°: spreading-type wetting. On the {100} wafers spreading took place regardless of wafer and flux compositions. The order of contact angles inferred from data observed for various combinations of wafers and fluxes is as follows: θ211⋍ θ110 > θ111θ100 = 0°. The order agrees with that of morphological importance determined by Bennema et al. except for the {100}. LPE garnet films are more wettable than GGG substrates, regardless of water orientation.

Growth and dissolution of liquid phase epitaxial garnet films in orthoferrite primary phase melt

Thick liquid phase epitaxial YIG (Y 3Fe 5O 12) films which had once grown on Gd 3Ga 5O 12 substrates from R 1 = [ Fe 2 O 3 ]/[ Y 2 O 3] = 14.0 and R 3 = [ PbO]/[ B 2 O 3] = 15.0 melts, dissolved into the melt during the prolonged time dipping process, while spontaneous nucleation of orthoferrite took place. Nevertheless, thin (15 μm) YIG films were available by short time dipping without orthoferrite nucleation. The phase diagram of the PbO-B 2O 3-Y 2O 3-Fe 2O 3 system was modified and had a narrower primary phase region of YIG than that reported by Robertson et al. The fact that thin garnet films are available even from the orthoferrite melt by short time dipping is attributed to a metastable behavior of LPE garnet films, which results from difference in the Gibbs free energy associated with nucleation between bulk orthoferrite and garnet films and from similar values of free energy of formation for both orthoferrite and garnet.

Optical absorption of liquid phase epitaxial garnet films at 1.3-μm wavelength for magneto-optic application

Optical absorption of liquid phase epitaxial magneto-optic Gd0.2Y2.8Fe5O12 films was measured at 1.3-μm wavelength using a waveguide technique. An optical absorption coefficient of α=0.2 cm−1 at 1.3 μm was obtained. This is the smallest value which has ever been reported for a garnet film and corresponds to 230 deg/dB in the figure of merit for Gd:YIG with the Faraday rotation coefficient of 200 deg/cm. α≤0.6 cm−1 is obtained, when garnet films are grown under the supercooling temperature of less than 10 °C. The supercooling temperature dependence of the α value is more insensitive for films grown from melts poor in B2O3 than for films from B2O3 rich melts. A mechanism of increase in optical absorption is discussed from the viewpoint of lead ion condensation at the solid/liquid interface and of incorporation into garnet films.

Surface morphologies and quality of thick liquid phase epitaxial garnet films for magneto-optic devices

Surface morphologies of thick Gd : YIG garnet films grown by liquid phase epitaxy (LPE) are found to be classified into three types: “mirror”, “striation” and “swirl”. “Mirror” appears when films are grown at low temperature or when the film thickness is small. “Striation”, which takes over the striation of the substrates, appears when the growth temperature or film thickness is medium. “Swirl” appears when the growth temperature is high or the film thickness is large. When “swirl” takes place, flux is included into the thick films. A mechanism for the morphological change with increase in film thickness is shown. An increase in half-width of the X-ray rocking curve with an increase in film thickness is found for the {111} films. This can be attributed to the generation of {110} and {211} facets which have larger lattice constants than the {111} and to crystallinity degradation due to flux inclusion. The {110} or the slightly misoriented {110} substrate is recommended to be employed so as to obtain inclusion-free thick films.

Pinning of 180° Bloch walls at etched nuclear tracks in LPE-grown iron garnet films

For increasing the magnetic-wall coercivity Hwc in liquid-phase epitaxial (LPE) ferrimagnetic garnet films of composition (Gd,Bi)3(Fe,Al,Ga)5O12, magnetic-wall ’’traps’’ are formed via bombardment by xenon ions with 180-MeV/ion energy and doses between 106 and 108 cm−2. For efficient wall pinning, the width of the nuclear damage tracks associated with the ion trajectories in the film have been enlarged to about the wall width by using a selective (chemical) etchant that makes use of the drastically increased etching rate in the damaged track volume. Therefore, channels of cylindrical or prismatic cross section are created having a width of a few 102 to about 103 Å and a length of more than 10 μm at the given etching conditions. The pinning capability of such channels can be further enhanced in films that are grown under planar compressive or tensile misfit strain. Then, strain relaxation occurs in the vicinity of these channels which results in steep gradients of the magnetic-wall energy via magnetostriction. These strain halos extend sufficiently beyond the channels so that efficient wall pinning is observed, even if the channel cross section is small compared with the wall width. Thermomagnetic compensation-point writing in LPE garnet film, that were treated accordingly, yield a pattern of stable magnetic domains of down to 8 μm in diameter in 3-μm-thick layers. The effect of etched nuclear tracks on the magnetic-wall coercivity can be interpreted satisfactorily with present models on Hwc.