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A pulsed inductive microwave magnetometer (PIMM) is used to examine magnetization dynamics. The thin film sample is brought into close proximity to the coplanar waveguide, which allows for simple changing of samples. The angle between the easy axis (e.a.) and field direction can easily be varied by rotation of the sample on the waveguide. The magnetization dynamics, i.e., precessional frequency, decay time, and precessional amplitude, are determined with respect to this angle or the bias field for epitaxial Fe1-xCox films with different anisotropies. The two precessional motions of a magnetic double layer (FeCo/Au/Ni80Fe20) where resolved with the PIMM, which is promising for future investigations on exchange coupled layers. [ABSTRACT FROM AUTHOR]

Couplers in general serve for galvanically isolated signal transmission between sensitive equipment. Standard opto-couplers are generally limited to a bandwidth of 25 MHz. However, with ever-increasing data transfer rates the need for couplers with much higher bandwidth is steadily growing. For this purpose magneto-couplers are very promising because their bandwidth is expected to be limited only by the Larmor precession of the magnetic moments with frequencies in the range of 1-10 GHz. In magneto-couplers the signal to be transmitted is converted into a current through a micro-coil. The resulting magnetic field is detected by a giant magnetoresistance (GMR) sensor element separated by an isolation layer. In the present case this element is a Wheatstone bridge consisting of four spin valves. The voltage across the bridge resulting from the magnetization change of the soft layers due to the field pulses is detected with a 1 GHz storage oscilloscope. Present experiments indicate a bandwidth larger than 500 MHz. After proper termination of the signal paths and applying a dc-bias field the rise time of the input signal of less than 1 ns is not increased by the coupler. Furthermore we show that the driving pulse may be completely reproduced in shape by applying external dc-bias fields. It will also be discussed how capacitive and inductive crosstalk between the coil and the spin valves and nonideal termination of the signal paths affect the achievable bandwidth. [ABSTRACT FROM AUTHOR]

Undulation instabilities of magnetic domains have been observed in nanostructured strips of a ferromagnetic Fe/Gd multilayer. The novel technique of magnetic transmission x-ray microscopy, which is based on the x-ray magnetic circular dichroism, was used for imaging. Below a critical magnetic field, sinus-like modulations of the magnetic domains could be observed. At a higher rate of field induced strain rectangular patterns occur. They seem to be characteristic for the reduced lateral width of the magnetic system and are in contrast to chevron patterns observed in extended systems. The domain morphologies found in different magnetic fields H, and in nanowires of various widths L[sub z], have been summarized in a H-L[sub z] "phase" diagram. An analogy with theoretical predictions for extended systems could be found. [ABSTRACT FROM AUTHOR]

The in-plane magnetic anisotropy of Fe films epitaxially grown on GaAs(001), in addition to a thickness-dependent four-fold contribution has a uniaxial component originating from the Fe/GaAs interface. This has been observed in several previous investigations. The orientation of the uniaxial easy axis (e.a.), however, was found to be along the [110] direction in most studies, but also an e.a. parallel to [-110] was reported in a few cases. It has been suggested that different reconstructions of the GaAs surface prior to Fe deposition could be responsible for this discrepancy. In the present contribution, it is shown that in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature the uniaxial anisotropy always has its easy axis along [110] with practically the same magnitude. In particular, the surface reconstruction of the GaAs substrate either (4×2) or (2×6) — has no effect on the resulting uniaxial magnetic anisotropy. This [together with recent results related to the phase transition of Fe/GaAs(001)] suggests that the same atomic configuration is formed at the Fe/GaAs(001) interface in both cases connected with the segregation of a certain amount of As (and Ga) to the surface. [ABSTRACT FROM AUTHOR]

Epitaxial Fe films in a thickness range from 4 to 64 monolayers (ML) were grown by molecular beam epitaxy on GaAs(110) at room temperature. The growth was characterized by reflection high energy electron diffraction. The magnetic in-plane anisotropy was investigated by alternating gradient magnetometry in a temperature range from 150 to 295 K. For a 64 ML thick Fe(110) film the [001] axis is the easy axis, the [-110] the intermediate axis, and the hard axis is between [-110] and [-111]. For Fe films with a thickness below 24.2±1.2 ML the [-110] becomes an easy axis at room temperature. A 24 ML Fe film shows a reorientation of the easy axis with decreasing temperature: Above the critical temperature of (251±3) K [-110] is the easy axis, for lower temperatures it becomes an intermediate axis. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Å Fe/4Å Gd)x75 multilayered FeGd system has been prepared on a 30 nm thin Si[sub 3]N[sub 4] membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record t! he images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Epitaxial Fe[sub 34]Co[sub 66] films in a thickness range from 3 to 100 monolayers (MLs) were grown by molecular beam epitaxy on GaAs(001) at room temperature. The growth was characterized by reflection high energy electron diffraction and x-ray diffraction. The magnetic properties were investigated by alternating gradient magnetometry magneto-optic Kerr effect, and superconducting quantum interference device magnetometry. The films show a strong interface-induced uniaxial in-plane anisotropy with the easy axis along [110]. In addition, the fourfold anisotropy coefficient changes sign around 6 ML i.e., the easy axis of the fourfold anisotropy switches from <110> to <100> with decreasing thickness. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The morphology, atomic magnetic moments, and in-plane magnetic anisotropies of ultrathin bcc Fe(001) films deposited by molecular beam epitaxy on ZnSe epilayers grown on GaAs(001) single crystal are reported. The growth mode and structure have been determined in situ by means of reflection high energy electron diffraction and Auger electron spectroscopy. The magnetic properties were characterized ex situ by an alternating gradient magnetometer, superconducting quantum interference device (SQUID) magnetometry, and conversion electron Mo¨ssbauer spectroscopy (CEMS). The Fe growth is epitaxial and occurs by three dimensional nucleation at the beginning. The coalescence of the islands is observed around 7 monolayers (ML). In agreement with SQUID results, CEMS measurements indicate no reduction of the Fe magnetic moment compared to the bulk value even for the first Fe monolayers. Determination of the in-plane anisotropy constants as function of the Fe thickness shows a strong interface-induced uniaxial in-plane magnetic anisotropy, which leads to a continuous evolution from a pure uniaxial anisotropy with easy axis along [110] direction for thickness below 10 ML to the pure bulk cubic Fe anisotropy above 40 ML. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A multilayered FeGd system sputtered on a Si[sub 3]N[sub 4]-membrane was used to demonstrate that magnetic transmission x-ray microscopy enables the imaging of the domain structure with high resolution in a quantitative way and in varying external magnetic fields. The field-dependent evolution of sub-100 nm out-of-plane magnetized domains, i.e., the transition from stripe into bubble domains, could be observed in detail. It has been shown that critical fields like the bubble collapse field can be described by a wall energy model. Contrary to the assumption of the theory, the magnetization does not remain perpendicular to the film plane in all cases. This is only true inside the bubbles. In the stripe domains the magnetic moments rotate. Their angle could be measured as a function of the external applied field. Internal stray fields can cause a rotation of moments leading to a contrast at the edges of stripe domains. The results indicate that the magnetization reversal in 3d/4f multilayers is not only determined by wall motions and is therefore more complex than previously assumed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In order to study sub-100-nm domains in magnetic multilayers a combination of three high-resolution imaging techniques has been applied to the same samples for the first time: magnetic force microscopy (MFM), Lorentz microscopy with a transmission electron microscope, and magnetic transmission x-ray microscopy (MTXM). The samples—atomically stacked [Fe(001)/Au(001)][sub n] multilayers with an approximate L1[sub 0]-lattice—were prepared by molecular beam epitaxy (MBE) on a GaAs(001) substrate which was then locally removed by laser-induced wet etching to create a window that is transparent for 200 keV electrons and soft x-rays. Magnetization curves with perpendicular and in-plane applied field indicate a spontaneous perpendicular magnetization with an equilibrium domain pattern in small fields and reversible wall motion. About 60 nm wide domains could be observed with MFM and MTXM, respectively. Lorentz images did not show any in-plane magnetic contrast, but the domain pattern appeared when the sample was tilted. This indicates that the magnetization is indeed strictly perpendicular. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High quality epitaxial Fe films were grown on GaAs(001) by molecular beam epitaxy and magnetron sputtering. Two-dimensional arrays of circular dots with 200 nm diameter and 500 nm period were made by interferometric lithography and ion beam etching. Large area patterning (about 1 cm2) allows integral magnetic measurements with an alternating gradient magnetometer. The magnetic behavior of thick patterned films is dominated by the demagnetizing field. Ultrathin continuous films and dot arrays of these show a strong uniaxial in-plane magnetic anisotropy with the easy axis in [110] direction which is fully conserved during the patterning process. This means that two stable remanent single domain states exist in ultrathin Fe(001) sub-μm dots on GaAs(001) because (i) the magnetostatic energy is not important due to the small aspect ratio, and (ii) the Fe/GaAs(001) interface creates a strong uniaxial in-plane magnetic anisotropy. Nanomagnets with these properties seem very attractive for high density memory elements. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that determined reversal processes in terbium/iron multilayer films. Information on the form of hysteresis; Remanence measurements; Evaluation of fluctuation fields and activation volumes for the series of films.