Robert A. Van Leeuwen

Magnetocrystalline and magnetoelastic anisotropy in epitaxial Co/Pd superlattices

We have used molecular‐beam epitaxy (MBE) to grow Co/Pd superlattices along the three high‐symmetry crystal axes: [001], [110], and [111]. Identical conditions were maintained for all depositions, and a series of samples of fixed Pd thickness (tPd = 10 ± 1 A) and varying Co thickness (2 A ≤ tCo ≤ 22 A) were prepared for each orientation. A variety of in situ and ex situ characterization studies were made, which confirm these superlattices are single crystalline for all growth directions. The dependence of the uniaxial magnetic anisotropy energy on the Co thickness in these superlattices showed significant systematic differences for each of the three crystal orientations. These variations result entirely from differences in the volume contribution to the anisotropy. Estimates of the magnetocrystalline and magnetoelastic contributions for the (111) and (001) samples are in good agreement with the measured anisotropy energies of these oriented superlattices.

Magnetic properties of epitaxial Co/Pd superlattices

A series of Co/Pd superlattices with constant Pd layer thickness of dPd = 11 A were grown on single‐crystal GaAs(110) substrates by molecular beam epitaxy (MBE). A buffer layer of 500 A of Pd provided an atomically smooth, fcc(111) single‐crystal starting surface for the superlattice deposition. The resulting superlattices maintain this crystal symmetry and smoothness throughout their epitaxial growth. Details of the structural characterization of these samples are given elsewhere in these proceedings. The magnetic properties of these films have been measured by vibrating sample magnetometry. A perpendicular easy axis is found for all seven of the superlattices presented (dCo = 2, 4, 8, 10, 12, 17, and 20 A). An unusually high coercive field of Hc = 6.6 kOe is observed for dCo = 2 A, and decreases monotonically with increasing dCo. The saturation magnetization agrees well with a model composed of bulk Co layers with an additional contribution from polarized Pd. The uniaxial magnetic anisotropy energy can ...

Effect of transition-metal overlayers on the perpendicular magnetism of MBE-grown, ultra-thin Co films

We have used in situ polar Kerr ellipticity measurements to study the perpendicular magnetic behavior of MBE‐grown Pd/Co/TM sandwich structures, where TM is the nonmagnetic transition metal overlayer Pd, Cu, or Ag. These structures are epitaxially deposited on thick Pd (111) buffer layers grown on Co‐seeded GaAs (110) substrates. Hysteresis curves were measured in situ for systematically varied Co and TM layer thicknesses 2 A≤tCo≤10 A and 0 A≤tTM≤200 A. We observed perpendicular loops with a coercive field of Hc≤200 Oe for the uncovered Co films for tCo≤6 A, becoming in‐plane above this thickness. However, subsequent deposition of just one atomic layer (≊2 A) of any of the TM over the Co resulted in strongly perpendicular, square hysteresis curves with Hc≥700 Oe for all films in the Co thickness range studied. Deposition of TM overlayers causes nonmonotonic behavior in Hc as a function of coverage. We find a peak in Hc at a TM coverage of tTM∼1.5 A for all materials, with a subsequent monotonic increase a...

Structural and magnetic properties of Ti/Co multilayers

We have investigated the structural and magnetic properties of sputter‐deposited Ti/Co multilayer thin films. Sample composition was determined by Rutherford backscattering spectrometry. The crystal structure and composition modulation were examined with several x‐ray diffraction techniques. X‐ray diffraction analysis showed that the Ti and Co layers grow in the hcp structure and that the films are strongly textured along the (002) direction and are structurally incoherent. Composition modulation was confirmed from low‐angle x‐ray diffraction measurements. Vibrating‐sample magnetometry (VSM) and Brillouin light scattering (BLS) were used to determine the magnetic properties of the films. VSM measurements of samples with Co layer thicknesses less than ≊22 A showed no measurable net magnetization, while those with greater Co layer thicknesses had both in‐plane and perpendicular components. Using a simple model, the measured thickness dependence of the magnetization can be explained by assuming that 11.3 A o...

Influence of structure on the magnetic anisotropy of Co/Pd (001) epitaxial superlattices

Abstract We have used molecular beam epitaxy to grow Co/Pd superlattices oriented along the fcc [001] crystal direction. A series of samples of fixed Pd thickness ( t Pd = 9±1A) and varying Co thickness (2≤t C o ≤8A) was prepared. The uniaxial magnetic anisotropy in these films displayed both a large perpendicular interface contribution and a large in-plane volume contribution. Using off-axial X-ray diffraction techniques to measure the fcc (113) Bragg reflection, the in-plane lattice spacing of three samples was directly measured. These measurements are consistent with a coherent strain model with the Co layers expanded in-plane by 8.0%±0.5% over that of bulk fcc Co. An estimate of the in-plane magnetoelastic energy calculated from this strain is in very good agreement with our observed volume anisotropy in these superlattices.

Influence of transition metal overlayers on the perpendicular magnetism of MBE-grown Co films

Abstract We have used in situ polar Kerr effect measurements to probe the magnetic behavior of MBE-grown Co films with and without overlayers of various non-magnetic transition metals (TM = Ag, Cu, Pd). We find a large peak in the coercivity, H c , near 2 A overlayer coverage for Ag and Cu.

Structural and Magnetic Properties of Epitaxial Co/Pd Superlattices

Recent interest in the magnetic and magneto-optic properties of transition metal/ transition metal multilayers has been stimulated by the discovery of perpendicular magnetism in particular systems.1,2 However, partially due to the large variety of thin-film deposition methods and growth conditions, it has been difficult to obtain a clear understanding of the mechanisms of interfacial magnetic anisotropy. In order to create controlled and well characterized interfaces, we have grown a series of epitaxial Co/Pd superlattices on single-crystal GaAs(110) substrates by Molecular Beam Epitaxy (MBE). This paper describes the growth procedure, structural characterization, and the magnetic and magneto-optic properties of these superlattices. Comparisons are made to a series of non-epitaxial, polycrystalline multilayers that were simultaneously deposited on Si substrates.

Sputtering and Molecular Beam Epitaxy (MBE) Deposition of Magneto-Optical Materials

Materials with anisotropies giving rise to perpendicular magnetization are important for optical data storage applications. However, the microscopic origin of the anisotropies is not well understood. It is now widely recognized that understanding the origin of surface and interface anisotropies is one of the most important problems in magnetism. Ultra-high vacuum deposition techniques allow the sequential deposition of layers of several elements with great regularity, and little interdiffusion and contamination at the interfaces. The microstructure of the resultant multilayer materials can vary from amorphous, or polycrystalline with only short range order, to high quality superlattices with long range structural coherence in all three dimensions. This paper gives an introduction to rare-earth/transitionmetal and transition-metal/transition-metal multilayers and superlattices. Sputtering and Molecular Beam Epitaxy (MBE) processes used to grow these materials are then described, as are the in situ and ex situ characterization techniques used to determine their electronic and physical structure, and to measure their magnetooptic properties. Some of the magnetic and magneto-optic properties of materials produced by sputtering and MBE related to optical data storage are discussed.