The magnetic domain structure in low anisotropy epitaxial garnet films

Single-crystal films of (YCa)₃(FeGe)₅O₁₂ garnets were prepared by the liquid phase epitaxial method on the (111) plane of Gd₃Ga₅O₁₂ substrates. These magnetic bubble domain films have comparable uniaxial anisotropy energy, cubic anisotropy energy and demagnetizing energy. A photographic technique was developed to measure the angles of inclination of the domain magnetization vectors with respect to the normal to the sample surface. Without an applied magnetic field these inclination angles were 58° and 122°. A simple stripe domain model was used to provide an explanation of the experimental results. This model can easily be extended for other types of mixed anisotropy cases.     

The effect of substrate defects on epitaxial magnetic garnet films

The stress patterns associated with various defects in Czochralski-grown gadolinium gallium garnet (GGG) crystals have been observed using a polarizing microscope. The effect of these defects on both the surface topography and the magnetic behaviour of epitaxial magnetic garnet films grown on GGG substrates is reported. In particular, iridium inclusions and defects of a filamentary nature affect the surface topography. Other types of defect influence the magnetic behaviour of the films in a manner attributable to a change in the lattice parameter.     

Rare earth-yttrium iron-gallium garnet epitaxial films for magnetic bubble domain applications

(RE,Y)₃(Fe,Ga)₅O₁₂ garnets, where RE=Eu or Gd, have been developed for use as magnetic bubble domain materials. Magnetic and crystallographic studies were used to find suitable compositions for epitaxial thin films on nonmagnetic garnet substrate crystals. Properties of films grown by liquid phase epitaxy on Czochralski Gd-Ga garnet (111) substrates are discussed. Uniaxial anisotropy in the films can be interpreted as being the result of a lattice mismatch stress mechanism. The Gd-Y films with uniaxial anisotropy are in tension while the Eu-Y films are in compression as shown by lattice spacing differences between films and their substrates. Uncracked, high stability Eu-Y films with very high compressive stresses were grown. Annealing experiments reveal significant changes in anisotropy which correlate with large changes in film lattice spacing. Thus, it is possible to obtain high uniaxial anisotropy in garnets containing only one kind of rare earth ion together with a nonmagnetic ion such as yttrium. These films support domains with very high wall velocities at typical device drive fields.     

Growth of epitaxial substituted garnet films by hydrothermal synthesis

A new hydrothermal technique is described in which the garnet synthesis is performed directly in the autoclave in low concentration basic solutions (NaOH or KOH). This method avoids a strong attack of the substrate and leads to uniform thickness and composition films. The best experimental conditions are given for the growth of Ga:YIG, Gd:Ga:YIG, Eu:Ga:YIG, Eu:Ga:ErIG and Gd:Ga:ErIG films on GdGaG substrates. Magnetic characterizations are presented and the properties of hydrothermal garnet films are discussed and compared with those of L.P.E. and C.V.D. garnet films.     

Chemical vapor deposition of epitaxial garnet films

The chemical vapor deposition of single crystal metal oxides has recently been extended to the growth of certain epitaxial garnets, in particular YIG on YAG and GdIG on YAG. The light green, transparent films aresim3muthick and are limited in area only by the area of the available YAG seeds. On     

Scintillation properties of the Ce-doped multicomponent garnet epitaxial films

(Lu,Y,Gd)₃(Al,Ga)₅O₁₂:Ce garnet scintillator single crystalline films were grown onto LuAG, YAG and GGG substrates by liquid phase epitaxy method. Absorption, radioluminescence spectra and photoluminescence excitation, emission spectra, and decay kinetics were measured. Photoelectron yield, its dependence on amplifier shaping time and energy resolution were determined to evaluate scintillation performance. Most of the samples exhibited strong UV emission caused by trapped excitons and/or Gd³⁺ 4f–4f transition. However, emission spectrum of the best performing Gd₂YAl₅O₁₂:Ce is dominated by the Ce³⁺ fast 5d–4f luminescence. This sample has outperformed photoelectron yield of all the garnet films studied so far.     

Features of the coercivity of strained epitaxial garnet ferrite films

We have studied the influence of the relative film-substrate lattice mismatch in the 0.5–0.85% range on the behavior of coercivity in epitaxial garnet ferrite (EGF) films with compositions (Bi, Sm, Lu, Ca)₃(Fe, Sc, Ga, Al)₅O₁₂ grown on (111)-oriented gadolinium gallium garnet (GGG) substrates. As the relative film-substrate lattice mismatch increases, the coercivity of EGF films initially grows, passes through a maximum, and then decreases. The maximum in the coercivity is related to periodic localized stresses caused by the formation of a misfit dislocation network whose period is comparable with the width of domain walls. The period of localized stresses is determined by the relative lattice mismatch between the EGF film and the GGG substrate.     

Laser annealing of gallium-substituted garnet epitaxial films in pressurized oxygen

The effects of laser annealing Ga-substituted EuYIG epitaxial films in still, controlled ambients of air and one to five atmospheres of pure oxygen have been studied. An approximately logarithmic increase in saturation magnetization (4pi M_{s}) and decrease in film magnetic Q factor were observed with increasing oxygen pressure in the annealing ambient. Compared with the most successful previous experiments, annealing at five atmospheres of oxygen displaced nearly twice the fraction of Ga from tetrahedral to octahedral lattice sites. As evidenced by the lack of film damage, the correlation of lattice parameter with the location of the Ga ions and the lack of broadening in the ferromagnetic resonance (FMR) lines, effective annealing temperatures above 1850K were achieved with no significant loss of oxygen from the films. The use of FMR to deduce the extent of film annealing was affirmed through the agreement of independent measurements of4piM_{s}by bubble statics and SQUID magnetometry in films indicated to be homogeneous by FMR.     

Optical absorption in cobalt-containing epitaxial films of gadolinium gallium garnet

The optical absorption of di-and trivalent cobalt ions embedded in single-crystalline films of gadolinium gallium garnet was observed in the samples grown by liquid-phase epitaxy from supercooled solution melts based on PbO-B₂O₃ and PbO-B₂O₃-GeO₂ systems.     

Determination of magnetic anisotropy constants for bubble garnet epitaxial films using field orientation dependence in ferromagnetic resonances

Cubic magnetocrystalline anisotropy constant K₁ as well as uniaxial anisotropy constant K_u and gyromagnetic ratio γ are precisely determined for (111) magnetic garnet epitaxial films from measurements on FMR field orientation dependence. Strict FMR conditions are derived from total free energy expressions, where the differences between magnetization direction and applied field direction are taken into consideration. By applying magnetic field in (110) plane, FMR is measured to obtain the three best fitting parameters of K₁, K_u and γ. Present analysis is compared with Cronemeyer et al's analysis. Influence of sample misalignment on measurement accuracy is also presented. Similarly, for (110) garnet films with orthorhombic magnetic anisotropy, measurements are carried out for two crystallographic planes of (001) and (110), and the four best fitting parameters of K₁, K_u, δ and γ are determined.     

Properties of Eu-Yb-Y magnetic garnet films grown by liquid phase epitaxy

Epitaxial films of Eu_yYb_zY_3?y?zFe_5?xGa_xO₁₂ have been deposited from PbO-B₂O₃ solution on (111) Gd₃Ga₅O₁₂ substrates. Saturation magnetization, characteristic length, coercivity, anisotropy and domain wall mobility are discussed in relation to film composition. The films exhibit reasonable mobilities, satisfactory quality factors and good temperature stability. The system appears to be a promising candidate for bubble device application.     

Control of the properties of magnetic garnet films

Large numbers of magnetic garnet films having essentially identical properties can be prepared from the same melt using the conventional LPE dipping technique, in which substrate rotation rate is adjusted to compensate for the difference between the growth temperature and the objective, thereby the growth rate can be completely controlled. Melt compositional drift has been suppressed by the periodic addition of garnet oxides and flux to the melt.     

The transient layer in magnetic garnet films grown by liquid phase epitaxy

A thin (～ 0.1 μm) layer is formed initially during the so-called “transient” period preceding the establishment of the steady state diffusion boundary layer in the melt, when films are dipped in a horizontal plane while undergoing axial rotation. Further evidence is given for the existence of the transient as a separate and distinct growth mode as compared to steady state growth. The transient layer, which grows comparatively rapidly, nevertheless has properties virtually identical to those of the subsequently grown steady state layer, except for its higher Pb concentration.     

Epitaxial iron garnet films with submicron diameter magnetic bubbles

Mixed rare earth iron garnet compositions have been developed in the form of epitaxial films which support submicron diameter magnetic bubbles. Sm_0.75Yb_2.25Fe₅O₁₂, Eu_0.9Yb_2.1Fe₅O₁₂ and Eu_1.2Lu_1.8Fe₅O₁₂ films on (111) Gd₃Ga₅O₁₂ as well as Sm_1.5Yb_1.5Fe₅O₁₂ and Eu_1.7Yb_1.3Fe₅O₁₂ films on (111) Sm₃Ga₅O₁₂ can be grown by an isothermal liquid phase epitaxy method. The effects of growth conditions on film composition and the lattice mismatch between a film and its substrate are discussed.     

Measurement of the physical thickness and refractive index of thin epitaxial garnet films

A technique for the measurement of refractive index and physical film thickness of epitaxial garnet films is described which utilizes variable wavelength measurements. Experimental results are presented for gadolinium gallium garnet substrates and two different bubble domain film compositions. From these results, it is concluded that the technique is not applicable to wafers with films on both sides due to the differences in film thickness of the two films. For single sided wafers, the refractive index can be determined with an accuracy of ±0.3 percent.     

Calcium germanium substituted iron garnet films for magnetic bubble applications

Mixed rare earth iron garnet films containing calcium and germanium have been grown on (111) oriented gadolinium gallium garnet (GGG) substrates. The effect of growth conditions on film composition and properties is discussed. The 5 μm diameter bubble films have good magnetic properties; however, temperature control during film growth is very critical.     

Linear birefringence control and magnetization in sputter-deposited magnetic garnet films

Birefringence control is essential in the fabrication of on-chip magnetooptic Faraday isolators. We report on film thickness and stress studies of birefringence in sputter-deposited single-layer bismuth-substituted iron garnet films and double-layer iron garnet films with gadolinium gallium garnet (GGG) covers. We examine compressively and tensilely strained films and analyze the photoelastic response of the sputter-deposited garnet films. We show that the net birefringence can be ed out under planar compressive strain conditions. Bilayer GGG on iron garnet film yields a reduced birefringence. Temperature control during the sputter deposition of the GGG cover is critical and strongly influences the magnetic moment and birefringence level in the waveguide. High-temperature deposition lowers the magnetization in the underlying iron garnet film.     

Substrate effects on the structure and optical properties of GaN epitaxial films

The phase composition and luminescent properties of GaN films grown by molecular beam epitaxy on (0001) sapphire and 6H-SiC substrates were studied. The films grown on SiC were found to consist only of the hexagonal phase and contain a lower concentration of impurities. Grains of cubic GaN, as well as donor and acceptor impurities, were found in the GaN film grown on sapphire. The formation of impurity centers is caused by the diffusion of oxygen and aluminum from the sapphire substrate during crystal growth.     

Control of the growth-induced magnetic anisotropy in ferrimagnetic garnet films grown by liquid-phase epitaxy

The influence of melt composition and growth temperature T_g on the growth-induced magnetic anisotropy constant K^g_u in Bi substituted LPE ferrimagnetic garnet films has been investigated. In films grown from Bi₂O₃ based and from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts the value of K^g_u increased upon decreasing T_g, associated with an increasing incorporation of B1. However, at given Bi content the films grown from Bi₂O₃ based fluxes generally exhibited smaller values of K^g_u than those from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts. The addition of small amounts of Ca²⁺ to the Bi₂O₃ based melts resulted in (Y,Bi)-garnet films changing from n- to p-type electrical conductivity at a minimum value of K^g_u. Additions of Si⁴⁺ to a $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melt reduced the uniaxial magnetic anisotropy of La-YIG-Ga films accompanied by a change from p- to n-type conductivity. Similarly, (Gd,Bi)-garnet films from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts changed from n- to p-type conductivity upon decreasing T_g where K^g_u changes sign from negative to positive. From the temperature dependence of the electrical conductivity the electron and hole concentrations in some of these films were estimated suggesting that the sign change of K^g_u in the investigated (Gd,Bi)-garnet films and the minimum of K^g_u in the investigated (Y,Bi)-garnet films and (La,Y)-garnet films occur at donor-acceptor compensation. This experimental evidence led us to conclude that the growth induced magnetic anisotropy may be correlated with the presence of donor and acceptor centers in the garnet structure.     

An optical investigation of transient layers in magnetic garnet films grown by liquid phase epitaxy

The growth of garnet films using Liquid Phase Epitaxy has led not only to materials with improved performance for bubble domain memories but to materials which exhibit improved microwave properties as well. We have investigated the optical properties of such films and found that there exist transient layers at the substrate/film interface and at the film/air interface. Our results and conclusions regarding the substrate/film interface do not agree with those of Davies et al⁽¹⁾. The discovery of a post growth lead rich layer has not been previously reported to our knowledge and has important implications for both bubble domain and optical applications of garnet films.