Oriented Garnet Films Research Articles

Second-harmonic generation studies of implantation defects depth profile in hydrogen implanted garnet film

We demonstrate that complete depth profile of structural defects induced by ion implantation, with spatially separated lattice strain and implant ion contributions can be obtained with the use of second-harmonic generation (SHG) effect. The SHG effect was measured in transmission geometry for (111)-oriented garnet films implanted with H2+ ions of 60 keV energy and 1.5 × 1016 cm−2 dose, and etched to different depths along implantation range. Extremely strong sensitivity of the measured SHG intensity patterns in implanted samples on angle of incidence was found. The integral d¯ and differential d¯′ depth profiles of nonlinear optical susceptibility tensor were obtained from the experiment with the use of a phenomenological model developed for crystals of C3v symmetry. Direct correlation between perpendicular strain-related part of d¯′ profile and the induced effective magnetic anisotropy field is shown. Prominent peak in d¯′ located much deeper than the strain profile range was found, and its origin as related to the effect induced by hydrogen presence in the garnet crystal structure was interpreted.

Nonlinear magnetization-induced terms in garnet film polarization in the second-harmonic generation effect: Theory and experiment

We demonstrate the presence of nonlinear magnetization-induced terms in magnetically ordered crystals in the second-harmonic generation (SHG) effect. The nonlinear terms have been evidenced experimentally in magnetic garnet film and explained theoretically in the frame of a developed phenomenological model. In the model, nonlinear medium polarization up to third order in magnetization is taken into account. We show that all the observed peculiarities of the SHG intensity, measured as a function of the external magnetic field and sample orientation, are in excellent agreement with the predictions of the theoretical model applied to the (111)-oriented garnet film. It is shown that the amplitude of cubic term in magnetization, about one third of the linear term, is required for the explanation of the experiment. It is also shown that the measurements of SHG intensity as a function of both the magnetic field and the sample orientation are necessary to reveal the existence of nonlinear magnetic terms in medium polarization.

Imaging capabilities of etched (100) and (210) garnet films

Imaging capabilities of etched (100) and (210) oriented garnet films are studied and compared. It is demonstrated that the etching of out-of-plane (100) garnet films may result in drastic reduction in saturation fields. Concurrently, the appreciable increase in contrast and resolution of images produced by the etched films has been observed.

Application of Magnetic Garnet Films for Magnetooptical Imaging of Magnetic Field Distributions

ABSTRACTRare-earth iron garnet films of high quality can be grown by liquid phase epitaxy on paramagnetic substrates of gadolinium galliumgarnet. Such films are currently used for imaging of the spatial distribution of magnetic fields. This application is based on the Faraday rotation which can strongly be enhanced by bismuth incorporation.The physical properties of the films can be controlled by the chemical composition, the growth conditions and the crystallographic orientation. The sensor properties like sensitivity, dynamic range, signal linearity and unambiguity must be optimized according to the application desired. These properties, however, are not independent of each other. In addition, they strongly depend on the optical wavelength. Thus, it is necessary to find compromises.The influence of Faraday rotation, Faraday ellipticity, optical absorption, magnetic anisotropies and film thickness on the performance of a magnetooptical indicator film is investigated. Based on the swing of the photoresponse, a new optimization process is introduced. The process is experimentally verified and application examples are demonstrated.Furthermore, two methods are presented to enhance the sensitivity of magnetooptical sensors. Using specific crystallographic orientations, an easy plane of magnetization can be induced which is inclined with respect to the film plane. If the magnetization lies in this plane a very high sensitivity is achieved. The dependence of the geometrical orientation of the easy plane on the growth direction is calculated and the sensitivity and dynamic range are derived. Experimental results of a [112] oriented garnet film are in good agreement with calculations.Garnet films which are magnetized along the film normal due to a strong induced uniaxial anisotropy support magnetic domains. If the collapse field perpendicular to the film plane is small, such films can be used as very sensitive indicator films. Such films are easier to prepare than sensitive in-plane films. However, the spatial resolution is limited by the size of the domains. This disadvantage can be avoided by applying a bias field in the film plane. Directly at the in-plane collapse field the sensor film is in-plane magnetized yielding high spatial resolution at still high sensitivity. The variation of magnetooptical images with in-plane induction is demonstrated. Experimental results are in agreement with calculations.

Sensitive magneto-optical sensors for visualization of magnetic fields using garnet films of specific orientations

Garnet films of high Faraday rotation are applied as magneto-optical sensors to visualize the spatial distribution of magnetic fields. Using specific orientations, the induced anisotropy can generate an easy plane of magnetization which is inclined with respect to the film plane. If the magnetization lies in this plane a very high sensitivity can be achieved. The dependence of the geometrical orientation of the easy plane on the growth direction is calculated and the sensitivity and dynamic range are derived. Experimental results of a [112] oriented garnet film are in good agreement with calculations.

Microdeformations of domain walls in (210)-oriented garnet films (abstract)

For appropriate values of perpendicular and in-plane magnetic fields, Hn and Hp, respectively, domain walls in (210) garnet films exhibit zig-zag and sinusoidal distortions along their lengths. Microdeformations of domain walls (DW) near these “instability loss lines”1 in the Hn, Hp plane were investigated in [1̄20]-oriented stripe domain structures by a dark-field magneto-optical technique. Changes of brightness and contrast of the image along and across the DW occur in response to an in-plane field Hp. Figure 1 shows a stripe domain structure with Hp=120 Oe along [001]. The analysis of the images2 confirms the presence of alternating DW parts inclined at angles ±α of about 3°–5° from the film normal. The domain-wall displacement varies through the film thickness as the result of the DW being pinned to the transitional level of the film–substrate interface. In the completely aligned stripe array, in-phase microdeformations have been observed for neighboring domain walls. With an increase of Hp, the DW parts with one direction of tilt are lengthened and the walls are reoriented from the [1̄20] to the [1̄21̄] direction. These results provide information on the spatial configuration of the deformed DW and give the possibility to create a more precise model of the domain and the domain wall in (210) garnet films.

A New Branch of the Spectrum of Single Domain Wall Excitations in Magnetic Garnet Films

180° and 90° domain walls in Bi-substituted [110] and [100] oriented garnet films with in-plane magnetization are studied by means of planar excitation-detection structures at microwave frequencies. New multiple resonance modes of single domain walls with very low linewidth (4.2 MHz) are observed at frequencies near 1 GHz. The resonances are excited by rf magnetic fields which are parallel or perpendicular to the wall plane. Resonance frequencies show a nonlinear dispersion dependence on the mode number. They decrease with an increasing static in-plane magnetic field normal to the wall plane. With decreasing film thickness the resonance frequencies increase. In addition the well known low-frequency resonances related to the wall translations or its flexural vibrations (Goldstone modes) are also observed in these samples.

Magnetooptical investigation of the deformation of domain walls in (210)-oriented garnet films

The analysis and investigation of dark-field images of domain in (210)-oriented garnet films testifies that under action of a planar field H x (oriented along the elongated domains) domain walls tilt from the normal to the film plane. The calculation of the distribution of light intensity in the microscope image plane for the suggested model of domain structure with inclined walls gives results which are in agreement with experiment.

Dynamical properties of domain walls in garnet films

Domain wall resonance (DWR) has been investigated in a parallel stripe lattice using a new high sensitivity DWR excitation and detection technique. Experiments were performed on garnets with pure uniaxial and orthorhombic anisotropy. A strong dependence of the DWR frequency on the intrinsic medium parameters, such as the saturation magnetization and the anisotropy constants, was observed. The influence on the domain oscillation frequency of an in-plane field applied parallel and perpendicular to the wall plane was analyzed and the corresponding changes of the wall mass and restoring constant was determined in (111)- and (110)-oriented garnet films.

High sensitivity RF detection of domain wall resonance in magnetic garnet films

A novel technique that improves both the coupling of the domain wall with the RF excitation field and the signal/noise ratio of the detected signal associated with the wall oscillations is reported. Measurements were made on full wafer garnets in a wideband resonance spectrometer with a nonresonant microstrip transmission excitation line. The problem of the standing wave ratio (SWR) change with RF frequency inherent in the reflection-type spectrometer is eliminated by using a subtraction mode of the digital oscilloscope. Large signals from normal and flexural wall modes are easily detected, and fine structures associated with magnetoelastic coupling are observed in [111]- and [110]-oriented garnet films with different magnetic parameters. >

Numerical simulation of wall dynamics in (111)-oriented garnet films in the presence of an in-plane magnetic field

The domain wall motion in the presence of an in-plane magnetic field Hy perpendicular to the wall is simulated using a fall implicit numerical scheme. Calculations are performed for the drive fields 0 Oe<Hz<15 Oe and in-plane fields -210 Oe⩽Hy⩽210 Oe. The relation between the average wall velocity v and the drive field Hz is discussed considering the wall structure. It was found that an in-plane field increases the peak velocity of the wall and extends the range of the drive fields, where the linear mobility relation is valid. A dynamical Bloch line stacking was found for sufficiently large drives. The influence of an in-plane field on the angular span of horizontal Bloch lines is discussed also. In particular the occurrence of 2π-horizontal Bloch lines is described. Numerical results obtained with a full implicit method are compared with the experimental observations of bubble motion and good agreement is found for |Hy|≤100 Oe.

Static and dynamic studies of bubble wall states in tilted ion implanted garnets

Two kinds of bubbles, small circular bubbles and normal elliptical bubbles, have been observed at the same bias field in [111] misoriented (YSm Lu Ca) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Fe Ge) <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> H+ implanted samples. Static and dynamic experiments were performed on these bubbles in order to characterize them. Strong in-plane orthorombic like anisotropy exists in these samples and these two kinds of bubbles may be correlated with the eight wall states observed by Konishi in [110] oriented garnet films. Transitions from normal to small bubbles occured only when the in-plane field was applied along the easy axis of magnetization of the implanted layer. The behaviour of closure domains seems to be preponderant for driving the observed transitions.

Static properties of magnetic bubbles in garnet films with orthorhombic anisotropy

The static properties of bubbles in (110) oriented garnet films of composition (Gd, Y)3 (Fe, Mn, Ga)5O12 have been studied. The anisotropy in these films is orthorhombic with the easy axis of magnetization perpendicular to the plane of the film and a secondary easy axis in the plane of the film. Two types of bubbles can be distinguished, A-type bubbles having no Bloch lines and B-type bubbles with Bloch lines. Magnetic fields parallel to the in-plane easy axis of magnetization have a strong influence on the diameter and on the collapse field. Whereas the properties of the B-type bubbles are independent of the sign of this in-plane field, the properties of the A-type bubbles do depend on the sign of this in-plane field. B-type bubbles easily change state and become A-type under influence of in-plane fields. At zero in-plane field the collapse fields of B-type bubbles are about 1 to 3% larger than the collapse fields of A-type bubbles. A theory is presented that takes into account the interaction between in-plane field and domain wall magnetization. In this way the experimental data obtained for the A-type bubbles are reproduced very well. The difference between the collapse fields of A- and B-type bubbles in zero in-plane field is explained by taking into account the influence of stray fields and Bloch lines on the domain wall energy.

Fast wall encoded magnetic bubbles in (110)-oriented garnet films with orthorhombic anisotropy: Statics

S=OC+ and S=OC-bubbles, which may be of potential interest for information storage, have been identified in several [110]-oriented garnet films with different compositions and material parameters. In all cases these bubbles were found to be stable at zero inplane-fields H ip. However, when one applies an inplane-field oriented parallel or antiparallel relative to the overall wall magnetization of S=OC±bubbles, their respective static collapse-fields increase or decrease. For a given H ip collapse-field differences of up to 24 Oe have been measured. Experiments and theoretical calculations clearly evidence that the inplane-field dependent collapse (and stripeout)-data are primarily influenced by the uniaxial and cubic anisotropy constants. Therefore it appears to be possible to tailor the stability range between collapse and stripeout where both bubble types are statically stable and to optimize the discrimination margin with respect to specific device requirements.

Replication of bubble states in a (110)-oriented garnet film with orthorhombic anisotropy

The replication of two kinds of bubbles found in a (110)-oriented garnet film, large and small elliptical bubbles, was tried by applying a single-chopping pulsed field to the respective stripe domains. The bubbles thus replicated from a seed bubble have the same size, shape, and static bubble collapse field as those of the seed bubble, which means that these two kinds of bubbles are replicated conserving their inherent domain wall structure.

New bubble garnet films with orthorhombic magnetic anisotropy and high mobility: (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG

New orthorhombic magnetic anisotropy garnet liquid phase epitaxial films with high mobility and low coercivity, (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG, have been successfully obtained. There are no hard bubbles, and wall states are either S = 0, 1, or −1. For 2 μm bubble material (YBi)3(FeGa)5O12/(110)GGG, mobility is μw = 85 m/s Oe and saturation velocity is Vs ≃130 m/s. For 6 μm bubble material (YTmBi)3(FeGa)5O12/(110)GGG, μw = 23 m/s Oe and Vs ≃130 m/s are observed. Vs ≃130 m/s for 2 μm bubble material assures bubble transfer at more than 10 MHz in a current access dual conductor device and utilization of the material for a magneto-optic readout head. Orthorhombic anisotropy for these materials is mostly growth induced. Growth-induced perpendicular anisotropies are not observed for eight other garnet systems on the (110)-GGG. Growth-induced orthorhombic anisotropy energy for Bi containing garnets is discussed using Gyorgy’s phenomenological parameters, A and B, compared with growth-induced anisotropy for (111)-oriented garnet films. A unique behavior of Y3+ in Bi containing garnets supports perpendicular anisotropy for orthorhombic anisotropy materials.

Static collapse discrimination of S = 0 bubbles in a garnet film with orthorhombic anisotropy

Four different types of circular S = 0 bubbles have been identified in a (110)-oriented garnet film with orthorhombic anisotropy, two at a time being large and small at the same bias field. Depending on the magnitude and sign (with respect to the [001] inplane easy axis) of an applied inplane field the S = 0 bubbles show a pronounced difference in their static collapse fields, for example, of up to 12.1 Oe at 50-Oe inplane field. This paper presents the static collapse characteristics of these S = 0 bubbles and a proposal for bubble state discrimination needed in wall state coded devices.

Magnetic bubbles with different wall states in a (110) oriented garnet film

In a (110) oriented (YTmBi)3(FeGa)5O12 garnet film with orthorhombic anisotropy, bubbles with different wall states were carefully studied using the bubble rocking method. Eight different bubble states have been identified, each belonging to a family of either large or small bubbles and coexisting at the same bias field. Each family is represented by elliptical S = 1,0,−1 and circular S = 0 bubbles. All bubbles have roughly the same mobility, whereas the static collapse fields differ as much as 6.1 Oe. Under all experimental conditions so far, we observed no conversion from small to large bubbles or vice versa, which indicates a remarkable stability of the two bubble families observed.

Ferromagnetic resonance relations in {111}-oriented garnet films

Microwave resonance relations for a {111} garnet film have been derived including the uniaxial as well as the first and second order cubic anisotropy contributions. Special attention has been given to the in-plane resonance condition. For this case the calculation has been made up to second order inK1/MH andK2/MH taking into account the influence of a nonideal in-plane configuration of the film.

Measurement of Cubic Anisotropy in (111)-Oriented Garnet Films

This paper describes a simple method for measuring the cubic anisotropy in garnet films. In (111)-oriented garnet films, the magnetization M is rotated from the film normal to the film plane by applying an in-plane field H//. The [111] component Mz of the magnetization M is measured magneto-optically. A plot of MzH// vs. Mz yields an approximately linear relation where the intercept of the line on the MzH// axis changes with the direction of H//, Thus, the cubic anisotropy K1 as well as the uniaxial anisotropy Ku can be estimated from the slope and the intercepts of the extrapolated straight lines for different directions of H//. This method is very simple and may be applied to films whose crystallographic axes in the film plane are unknown. With an adequate choice of the azimuth of the in-plane field, K1 has been estimated with an accuracy of 30%.