J.‐P. Krumme

Bismuth iron garnet films prepared by rf magnetron sputtering

We report on the growth of highly bismuth‐substituted iron garnet films by rf magnetron sputtering in a pure argon plasma. Under special conditions the target composition is fully reproduced in the films. Film homogeneity in the noncrystalline state is excellent. Crystallization on lattice‐matched garnet substrates occurring during growth above 520 °C substrate temperature and by post‐annealing above 650 °C yields the garnet phase, as inferred from the optical and magneto‐optic spectra and the saturation magnetization. Residual imperfections appearing after crystallization need further elucidation. We cope with the extreme disparity in the elemental sputter yields of the mixture Gd‐Bi‐Fe‐Al‐Ga‐O by (i) protecting the growing film from ion bombardment in using a magnetron source and (ii) binding Bi to a more slowly sputtering species, such as in BiFeO3.

Selected‐area sputter epitaxy of iron‐garnet films

The growth of single‐crystal bismuth iron‐garnet films by in situ sputter epitaxy has been extended to ‘‘selected‐area sputter epitaxy’’ (SASE) where epitaxial growth is locally impeded by low‐energy (102 eV) ion bombardment of the substrate from an argon plasma before film deposition. Then, in a critical range of substrate temperatures, a pattern of epitaxial and amorphous patches evolves during deposition with high geometrical resolution. The optical and structural properties of both SASE phases are investigated.

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 A 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 magnetostrict...

MOPS, a magneto‐optic‐photoconductor sandwich for optical information storage

A magneto‐optic photoconductor sandwich, called MOPS, has been assessed as a memory medium for optical information storage. The present version of MOPS is composed of an epitaxial (Gd,Bi)3 (Fe,Ga)5O12 film and a Cu‐doped CdS photoconductor film between coplanar In2O3/SnO2 electrodes. The chip contains 1.4×105 bits, requires 1 μW of optical power at 6328 A for switching a memory cell in a magnetic field of 100 Oe and electric field of 1.2×104 V/cm, exhibits a read‐out contrast of 21 : 1 at a read‐out efficiency of 0.1%, and has a cycle time of ∼100 μs. MOPS has not been degraded by 107 switching cycles of arbitrary memory cells. No cross talk between neighboring bit sites has been observed.

Optical recording aspects of rf magnetron‐sputtered iron‐garnet films

The intrinsic magneto‐optical readout performance in reflection is calculated for bismuth and cobalt‐substituted iron‐garnet films on a multilayer interference mirror at 800‐, 633‐, 488‐, and 420‐nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare‐earth transition‐metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare‐earth transition‐metal films at blue to near‐ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rare‐earth transition‐metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording.This compara...

A highly sensitive reversible and nonvolatile hybrid photoconductive/magneto‐optic storage material

The optical recording sensitivity of magneto‐optic memory materials can be greatly enhanced by combining their physical stability and reversibility with the high optical sensitivity of certain photoconductors. Feasibility experiments have been performed on a magneto‐optic–photoconductor sandwich (called MOPS) of a liquid‐phase epitaxial ferrimagnetic garnet film at its magnetic compensation temperature covered by a Cu‐doped CdS temperature covered by a Cu‐doped CdS film and electrodes. Using a HeNe laser a recording sensitivity, referred to 1% read‐out efficiency, of better than 1 μJ/mm2 % at magnetic switching fields <100 Oe and ≳400 Hz repetition rate has been achieved. 106 switching events have not degraded the performance of MOPS.

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

Abstract The influence of melt composition and growth temperature Tg on the growth-induced magnetic anisotropy constant Kgu in Bi substituted LPE ferrimagnetic garnet films has been investigated. In films grown from Bi2O3 based and from PbO B 2 O 3 based melts the value of Kgu increased upon decreasing Tg, associated with an increasing incorporation of B1. However, at given Bi content the films grown from Bi2O3 based fluxes generally exhibited smaller values of Kgu than those from PbO B 2 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 Kgu. Additions of Si4+ to a PbO B 2 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 PbO B 2 O 3 based melts changed from n- to p-type conductivity upon decreasing Tg where Kgu 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 Kgu in the investigated (Gd,Bi)-garnet films and the minimum of Kgu 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.

Magnetoelastic and optoelastic coupling in (111)‐ and (110)‐oriented bismuth‐iron garnet films prepared by sputter epitaxy

High‐quality iron‐garnet films of composition Gd3−vBivFe5−w−x−yGdw GaxAlyO12−zArz with 1.02≤v≤1.45, 0.01≤w≤0.36, 0.22≤x≤0.24, 0.26≤y≤0.38, and 0.002≤z≤0.014 have been grown epitaxially on (111)‐ and (110)‐oriented gallium garnet substrates with the lattice constant in the range 1.2475≤a0(nm)≤1.2553 by rf magnetron sputtering in argon plasma. For the study of the optoelastic and magnetoelastic properties of these sputter‐epitaxial films the lattice mismatch Δa⊥=as−a⊥f has been varied in the range −1.7<Δa⊥(10−2 nm)<0.5 by using substrates with various lattice constants. The near‐infrared optical anisotropy normal to (Δnxy) and in the plane (Δnyz) of (110)‐oriented films turn out to depend linearly on Δa⊥ over this large range of lattice misfits. No growth‐induced contribution has been observed. The same behavior is found for the induced uniaxial (K⊥) and in‐plane (K∥) magnetic anisotropy constants at room temperature. The optoelastic coefficients P44 and ΔP, as well as the magnetostriction constants λ111 an...

Determination of the local variation of the magnetic properties of liquid‐phase epitaxial iron garnet films

This paper supplements and assesses an optical measuring technique for the local determination of the cubic and uniaxial anisotropy fields K1/Ms and Ku/Ms in uniaxial magnetic films reported in a recent paper. Graphs for the quick evaluation of the Ku/Ms values are given. The accuracy of the method is assessed by comparison with FMR measurements. The origin of the nonuniformity in the domain pattern of a (111) LPE garnet film with the chemical composition Y2.5Gd0.5Fe4Ga1O12 grown on a GGG substrate is investigated by local optical measurements of the magnetic film parameters K1/Ms, Ku/Ms, compensation temperature, and magneto‐optic Faraday rotation. It is correlated with local structural parameters of the substrate as stress birefringence from ellipsometric measurements and inhomogeneity of the lattice constant measured by x‐ray topography.

Surface segregation and preferential sputtering of bismuth in rf‐magnetron‐sputtered iron‐garnet films

Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and secondary‐ion mass spectrometry have been used to elucidate the role of surface segregation and preferential sputtering of bismuth in rf‐magnetron‐sputtered bismuth–iron‐garnet films. It turns out that bismuth is enriched by a factor of up to 2.4, as compared to the bulk content, within the first 1–1.5 nm beneath the advancing film surface during growth. Furthermore, Ar+‐ion bombardment at projectile energies as low as 50 eV gives rise to a rather complete depletion of bismuth in the garnet surface. As neither surface segregation nor preferential sputtering of bismuth can be observed in as‐polished single‐crystalline Bi12SiO20 used as our reference, we conclude that the bond strength between bismuth and oxygen is weaker than that of the other garnet constituents. This is confirmed by comparing the calculated sputter yield of the element oxide. Thus, bismuth‐rich crystallographically perfect epitaxial iron‐garnet films can only be grown by ...