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Notes: Ferromagnetic alloy films of bcc FexCo1−x(001) were epitaxially grown on ZnSe-epilayered GaAs substrates spanning both the thermodynamically allowed bcc regime (0.25〈x≤1) and the epitaxy-extended metastable bcc regime (0≤x≤0.25). Conversion-electron extended x-ray absorption fine-structure (EXAFS) and reflection high-energy electron-diffraction (RHEED) measurements verify that metastable bcc FexCo1−x films with 0≤x≤0.25 are stabilized by epitaxy on ZnSe. Additionally, the composition-dependent magnetic properties of these films were characterized by ferromagnetic resonance and vibrating sample magnetometry.

Notes: The reflectivity spectra from single-crystal epilayers of the diluted magnetic semiconductor Zn1−x Cox Se(x=0.0076, x=0.0104) have been studied as functions of magnetic field and temperature. The excitonic spin splitting in these crystals saturates for magnetic fields B〉5 T, indicating that (Zn,Co)Se is a Brillouin paramagnet, in agreement with magnetization and electron-paramagnetic-resonance studies on the same samples. The magnetoreflectivity data yield a value for the exchange parameter difference N0 (α−β)=2420±40 meV, significantly larger than the values obtained for either Fe- or Mn-based diluted magnetic semiconductors studied to date.

Notes: Trilayers of CoFe/Mn/CoFe(001) have been prepared by molecular beam epitaxy and their magnetic properties measured by magnetometry and ferromagnetic resonance. Very strong near-90° coupling between the CoFe layers, with no evidence for 180° coupling, was found in all but the thickest Mn-layer samples. The coupling energy has the form suggested recently for the case when the interlayer itself is antiferromagnetic. An analysis of the ferromagnetic resonance data indicates that the magnitude of the coupling oscillates with the Mn thickness. © 1996 American Institute of Physics.

Notes: We have examined the initial interface formation and subsequent film growth for Fe films on the As-terminated (2×4) reconstructed surface of GaAs(001) in an effort to correlate the initial adsorption sites and film growth with the magnetic anisotropy. The growth and surface studies were performed in a four chamber ultrahigh vacuum system which incorporates UHV sample transfer between the chambers for III–V semiconductor growth, metal growth, photoelectron diffraction (PED), and scanning tunneling microscopy (STM). After coating with a thin film of Au (40 A(ring)) at room temperature, the samples were removed from the system for postgrowth characterization, which included ferromagnetic resonance and magnetometry. The GaAs(001) surface was prepared via homoepitaxial growth by MBE, with the growth terminated in a manner which resulted in a well-ordered As-dimer terminated (2×4) reconstructed surface as revealed by reflection high energy electron diffraction and STM. Fe deposition was performed in a second MBE chamber for coverages which ranged from 0.1 ML to several tens of monolayers at a substrate temperature of 175 °C.The sample was then transferred under UHV to either the PED or STM chamber to determine the initial adsorption sites, growth mode, and evolution of film structure with increasing coverage. For the lowest coverages studied (0.1 ML), we obtain evidence for preferential adsorption at As-dimer sites. At a coverage of 1 ML, two-dimensional islands form approximately 20 A(ring) in size, but elongated along the missing dimer rows with an aspect ratio of 2:1. At high coverages ((approximately-greater-than)40 A(ring)), we observe three-dimensional mounds or clusters with an average in-plane diameter of approximately 100 A(ring) and a narrow size distribution. Even at this coverage, the monolayer terraces of the GaAs substrate are clearly visible in the STM image, with the Fe film uniformly growing on each terrace. Photoelectron diffraction in the forward scattering regime (high electron kinetic energy) is utilized to determined the growth mode. At low kinetic energy, information on the adsorption site is obtained from Auger electron diffraction and compared with the results of the real space STM images.

Notes: We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co,Ni,Fe) on (001) diamonds, the thickness of the films varying between a few tenths of a nanometer to over 100 nm. The crystalline quality and fourfold symmetry of these layers was monitored in situ during the film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout each entire film. The magnetic characterization was performed with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops. The saturation magnetization of the Co films is only slightly lower than the literature values. The coercive fields are very small (∼25 Oe) and the magnetization reversal very sharp. The FMR yielded a fourfold anisotropy comparable to literature values. The observation of the first standing spinwaves underlines the good quality. The Ni films are tetragonally distorted due to the 1.2% mismatch. The FMR data indicate a significant perpendicular anisotropy slightly smaller than 4πM, the fourfold in-plane anisotropy being comparable to the bulk value. The saturation magnetization is reduced by 30% compared to bulk values, probably due to nickel-carbide which was observed in the XRD data from some samples. Neither the in-plane 〈110〉 nor the in-plane 〈100〉 axis show an easy axis behavior and both require fields in excess of 6000 Oe to saturate, the coercive fields being about 200 Oe. The RHEED patterns of the Fe films show single crystal growth with a lattice constant comparable to diamond, indicating an fcc structure. A similar structural and magnetic characterization of these films will also be presented. © 1996 American Institute of Physics.

Notes: Oriented single-crystalline thin films of Fe3O4 and superlattices of Fe3O4/NiO have been grown using molecular-beam-epitaxy techniques on polished substrates of MgO(001). The 1–2-μm-thick superlattices have their Fe3O4 layer thicknesses held constant at 68 A(ring) and the NiO thickness varied from 8.5 to 102 A(ring). We report the initial ferromagnetic resonance measurements made on these samples to investigate the effects that interfacial lattice distortion and interlayer coupling have on their magnetic ordering and anisotropy. These results are compared with structural and magnetic studies made on the same films using x-ray diffraction and magnetometry techniques. We find clear evidence in the trends of both the ferromagnetic resonance fields and the linewidths as a function of NiO thickness that coupling between the layers can change the in-plane anisotropy and the overall magnetic response. The single-layer Fe3O4-only sample behaves essentially like bulk magnetite.

Notes: Investigation of polycrystalline diamond films by electron paramagnetic resonance at 9.5 and 35 GHZ has revealed the presence of forbidden transitions resulting from a simultaneous microwave induced flipping of unpaired electron spins and environmental nuclear spins. The spacing of the resonance lines identifies hydrogen as the atom neighboring the paramagnetic active site.

Notes: We have made spin-valve structures of Permalloy/Cu/Co by sputtering or electron-beam deposition onto the antiferromagnetic oxide NiO. The oxides were made either by deposition of the metals and subsequent oxidation or by growing them in situ using reactive sputtering. The magnetic properties of the giant magnetoresistance structures were studied by magnetoresistance, vibrating sample magnetometry, and ferromagnetic resonance methods. The oxides were characterized by x-ray diffraction and atomic force microscopy. We studied surface roughness and structure as functions of thickness and oxidation temperature and correlated the oxide properties with the magnetic performance. We found that the metal layer roughened during the postdeposition oxidation process and that the resulting oxide layers were very effective in pinning the direction of the magnetic moment of adjacent metal films. Coercive fields over 500 Oe were obtained for Co overlayers on NiO films but the exchange bias field was generally less than 100 Oe and was not strongly dependent on the roughness. The beneficial effects of this strong pinning were offset to some degree by higher switching fields required in spin-valve structures deposited over the Co. We also made reactively sputtered oxide antiferromagnetic films which had smoother surfaces than those made by postdeposition oxidation.

Notes: Sensitivity to magnetic atoms and low intrinsic absorption characterize the interaction of neutrons with matter. Consequently, polarized neutron reflectivity provides a unique means of performing depth-resolved vector magnetometry. We have used this technique to determine the magnetization depth profiles of Fe/Cr superlattices. Superlattices of bilayer composition [55 A(ring) Fe/17 A(ring) Cr], grown at 523 K, exhibit biquadratic coupling with large saturation fields (∼3 kOe), while those grown at 293 K are ferromagnetically ordered. We have directly measured the evolution of the coupling angle between adjacent Fe layers as a function of applied field and will discuss how bilinear, biquadratic, and external field terms produce the observed order. The weaker coupling found in the Fe/Al system makes possible the investigation of a range of spin configurations at temperatures that do not endanger the sample. We have mapped the phase diagram of a [42 A(ring) Fe/12 A(ring) Al/39 A(ring) Fe] (100) trilayer and find evidence of biquadratic coupling at low temperatures and fields (e.g., when H=180 Oe, the Fe layer spins relax away from ferromagnetic alignment below T≈170 K). Our measurements agree qualitatively with energy minimization calculations and the results of bulk magnetometry.

Notes: The temperature dependence of the unusual magnetic 90° coupling in epitaxial Fe/Al/Fe(001) trilayers has been determined. For specific values of applied field and temperature, in-plane anisotropy and the interlayer coupling drive abrupt first-order changes in the temperature-dependent moment of these trilayers. The occurrence of such a first-order transition can be used to determine the value of the interlayer coupling constant, JQ, at the transition temperature. We show that Fe/Al/Fe(001) trilayers also exhibit distinct second-order transitions in the temperature-dependent moment, and that the occurrence of a second-order transition can similarly be used to specify JQ(T). A comparison is made of the values of JQ(T) determined by these two approaches, and the dependence of JQ on T is analyzed.