C. H. Wilts

Determination of magnetic profiles in implanted garnets using ferromagnetic resonance

Magnetic properties of the implanted layer in thin garnet films can be obtained from ferromagnetic resonance experiments. Approximate profiles of implantation induced anisotropy can be obtained using perpendicular resonance alone. For maximum information and accuracy, both perpendicular and parallel resonance spectra are needed, and measurements should be made on a number of samples from which varying amounts of the implanted layer have been removed by ion milling. For narrow linewidth materials it is possible to deduce profiles of H k , 4πM, and A and to determine the value of g in the implanted layer. Methods are presented for the accurate calculation of parallel ferromagnetic resonance (FMR) spectra with depth varying magnetic parameters. This method of analysis has been successfully applied to a yttrium iron garnet (YIG) film substituted with Gd, Tm, Ga, and implanted with He ions at 140 keV with a density of 3 × 1015cm-2.

X‐ray rocking curve and ferromagnetic resonance investigations of ion‐implanted magnetic garnet

Detailed analyses of x-ray rocking curves and ferromagnetic resonance spectra were used to characterize properties of -oriented Gd, Tm, Ga:YIG films implanted with Ne+, He+, and H + 2 . For each implanted species the range of doses begins with easily analyzed effects and ends with paramagnetism or amorphousness. Ion energies were chosen to produce implanted layer thicknesses of 3000 to 6000 A. Profiles of normal strain, lateral strain, and damage were obtained. The normal strain increases with dose and near amorphousness is 2.5%, 3.4%, and 3.9% for Ne+, He+, and H + 2 , respectively. Lateral strain is 0 for all values of normal strain, implying absence of plastic flow. Comparison of these results with the reported decrease in lateral stress implies either a large reduction in Youngs modulus or a transition to rhombohedral equilibrium unit cell. Damage is modelled by a spherically-symmetric Gaussian distribution of incoherent atomic displacements. Due to the use of (444), (888), and (880) reflections the sensitivity is greatest for the c sites occupied by Gd, Tm, and Y. The standard deviation of displacements increases linearly with strain with proportionality constant 0.25, 0.18, and 0.13 A/% for Ne+, He+, and H + 2 , respectively. For maximum strains up to 1.3% annealing in air reduces the strain without changing the shape of the profile. The behavior of the strain with annealing is nearly independent of implanted species or doses. After annealing at 600 °C the strain is 40% of the original value. Magnetic profiles obtained before and after annealing were compared with the strain profiles. The local change in anisotropy field DeltaHk with increasing strain shows an initially linear rise for both He+ and Ne+. The slope is −4.1 kOe/%, in agreement with the magnetostriction effect estimated from the composition. For strain values between 1 and 1.5%, DeltaHk saturates reaching peak values of −3.6 kOe for He+ and −2.8 kOe for Ne+. At strain values near 2.3% for He+ and 1.8% for Ne+, DeltaHk drops to nearly 0 and the material is paramagnetic. For peak strains greater than 1.3% for He+ and 1.1% for Ne+ the relation between uniaxial anisotropy and strain is not unique. The saturation magnetization 4piM, the ratio of exchange stiffness to magnetization (A/M) and the cubic anisotropy H1 decrease with strain reaching 0 at 2.3% and 1.8% for He+ and Ne+, respectively. At these strain values the damping coefficient alpha is 50% and 80% greater than bulk value for He+ and Ne+, respectively. For higher observed strains the material remains paramagnetic. Upon annealing of samples implanted with low doses of Ne+ and He+ the anisotropy field follows uniquely the behavior with strain for unannealed material. At 600 °C the magnetization returns to bulk value but the ratio A/M remains 20% low. For H + 2 implantation the total DeltaHk consists of a magnetostrictive contribution due to strain and of a comparable excess contribution associated with the local concentration of hydrogen. The profile of excess DeltaHk agrees with calculated LSS range. The presence of hydrogen results in a reduction of 4piM not attributable to strain or damage. For a peak strain of 0.60% and a peak total DeltaHk of −4.5 kOe, the magnetization is only 40% of bulk value. After annealing up to 350 °C the excess DeltaHk diminishes and redistributes itself to the regions neighboring the peak damage. At 400 °C the excess is nearly 0. For higher annealing temperatures the only component of DeltaHk is magnetostrictive. At 600 °C, the magnetization, the ratio A/M, and alpha return to bulk values.

Frequency dependence of the parallel and perpendicular ferromagnetic resonance linewidth in Permalloy films, 2‐36 GHz

Ferromagnetic resonance linewidth data for 75% Ni‐25% Fe evaporated thin films at 2–36 GHz for both parallel and perpendicular orientations show that the two linewidths are the same and increase linearly with frequency above 10 GHz. At lower frequencies the parallel linewidth is in accord with the high‐frequency behavior, but the perpendicular linewidth levels off at 10–30 Oe. These data suggest that the high‐frequency relaxation is characteristic of a Landau‐Lifshitz λ‐type process but that the low‐frequency losses are characteristic of a process intermediate between λ‐type and 1/τ‐type relaxation.

Magnetic Anisotropy in Flat Ferromagnetic Films: A Review

A review of those characteristics of the anisotropy found in thin Fe–Ni–Co films that are important from a practical viewpoint are presented. Previously published data are supplemented to form a composite ternary diagram of anisotropy field Hk as a function of composition for the alloy system Fe–Ni–Co for 250°C substrate temperature. Anisotropy fields as a function of composition for the three binary alloy systems at other substrate temperatures are included. A composite diagram showing anisotropy field as a function of measuring temperature illustrates the need for temperature stability. Magnetic annealing and aging is discussed. Finally the importance of magnetostriction as a source of the anisotropy is discussed in detail as well as pair ordering. It is concluded that no single source or combination satisfactorily describes the origin of the anisotropy.

Relaxation Processes for Ferromagnetic Resonance in Thin Films

Ferromagnetic‐resonance linewidth measurements have been made for two hundred Ni–Fe alloy films (77% Ni) 150–3200 A thick at frequencies from 1–9 Gc/sec with the static field in the film plane. To avoid dispersion effects samples with the smallest linewidth (ΔHmin) were selected for each thickness. For film thickness less than a frequency‐dependent critical thickness Dω, ΔHmin is independent of film thickness. For thicker films where D > Dω, ΔHmin increases linearly with film thickness. The observed Dω values (about 1000 A) are in good agreement with predictions based on magnon scattering involving spin waves degenerate with the uniform mode. Because of the magnetostatic mode modification of the spin‐wave dispersion relation for thin films there are no spin‐wave states degenerate with the uniform mode for D < Dω and magnon scattering is not allowed. The applicability of two different magnon processes, s‐d exchange and two‐magnon scattering, is discussed. Neither mechanism provides a completely satisfactor...

Lorentz Microscopy Determination of Domain‐Wall Width in Thick Ferromagnetic Films

Width of the 180° domain wall in Ni–Fe alloy films as a function of film thickness up to 1800 A was measured using the defocused mode of Lorentz microscopy. For the thinner films, the measured wall widths are in good agreement with earlier data obtained by Fuchs. For films thicker than 800 A, the wall width increases with film thickness to about 9000 A at 1800 A film thickness. The validity of the classical determination of wall width is discussed.

Ferromagnetic resonance study of the anisotropy profile in implanted bubble garnets

A method for determining the magnetic anisotropy profile of an ion‐implanted garnet layer is presented. To do this the eigenvalue equation for spin waves is solved numerically for a system consisting of a very thick film with uniform perpendicular anisotropy and a surface layer in which the anisotropy varies through the surface. Results of this calculation are matched to experimental FMR data from samples cut from the same wafer but etched by different amounts. A measurement of the exchange constant in the implanted layer may be possible if two or more surface modes are visible. The anisotropy profiles of samples implanted with 2×1014 Ne+/cm2 at 50, 100, and 150 keV were reconstructed in this manner. The profile was found to show a broad peak centered at a depth somewhat shallower than the projection range for Ne+ at the appropriate energy. The value of the change in anisotropy was shown to match that predicted from a magnetostrictive origin and the measured change in lattice constant in the surface layer...

Amplitude of ferromagnetic spin‐wave resonance in thin films

The effect of conductivity on the spin‐wave spectrum of thin Permalloy ferromagnetic films has been investigated. If conductivity effects are included and a simple surface anisotropy is assumed, it is known that the calculated mode locations and amplitudes for Permalloy films are in excellent agreement with some experimental data in the range 800–2700 A in thickness. If conductivity effects are omitted, a much simpler calculation is possible, but the error in mode location and amplitude has been unknown. For both perpendicular and parallel resonance geometries, detailed calculations reported here have shown that mode locations are not significantly affected over the above thickness range, and that the main mode amplitude is in error by only 20% at 800 A thickness. However, for 2000 A thickness, the main mode amplitude is in error by a factor of 2.5.

Ferromagnetic resonance study of the anisotropy field and nonmagnetic regions in implanted layers of bubble garnet films

The effects of implantation dose and annealing on the anisotropy field of the implanted layer in bubble garnet films were investigated by ferromagnetic resonance. For large implantation dose, the existence of a nonmagnetic layer inside the implanted layer was verified and its boundaries were located. For smaller doses, the implanted region remains magnetic, but the negative shift in anisotropy field increases and the exchange constant decreases with increasing dose. For intermediate dose an internal nonmagnetic layer is created with a surface magnetic layer which resonates as an uncoupled region. The nonmagnetic layer extends to the surface at higher dose, and its thickness increases with increasing implantation dose.

Dependence of Magnetic Anisotropy on the Crystal Structure of Ni–Fe Thin Films

The induced magnetic anisotropy of Ni–Fe films has been shown to be related to the crystal structure of the film. By use of electron diffraction, the crystal structure of vacuum‐deposited films was determined over the composition range 5% to 85% Ni, with substrate temperature during deposition at various temperatures in the range 25° to 500°C. The films were deposited on single‐crystal NaCl substrates. The phase diagram determined in this way has boundaries which are in fair agreement with the equilibrium boundaries for bulk material above 400°C and deviate markedly below 300°C. The (α+γ) mixture phase disappears below 100°C. Although epitaxial growth occurs at high temperatures, the existence or absence of epitaxy has no significant effect on the type of crystal growth.Comparison of these data with measured values of the anisotropy energy indicates that the anisotropy is strongly sensitive to structure. The anisotropy energy for γ structure is about 2½ times larger than for α structure at the composition...