J. E. Mattson

Non-oscillatory antiferromagnetic coupling in sputtered Fe/Si superlattices

A series of sputtered Fe(30{Angstrom})/Si(x) superlattices were grown for x=10--40{Angstrom}. Magnetization and Kerr hysteresis loops, and neutron-reflectively measurements identify antiferromagnetic (AF) coupling of the Fe layers at room temperature for x=15{Angstrom} nominal thickness, with switching fields of 6kOe. X-ray structural analysis indicate that the spacer medium is crystalline for x<20{Angstrom}, while sputtered Si is amorphous (a). Failure to detect oscillations in the AF coupling for thicker Si layers is due to the formation of a-Si, as opposed to the crystalline silicide responsible for the coupling.

150% magnetoresistance in sputtered Fe/Cr(100) superlattices

We report the epitaxial growth of Fe/Cr(100) superlattices onto MgO(100) single‐crystal substrates by magnetron sputtering. Superlattices that are epitaxially oriented within 1° both in‐plane and out‐of‐plane with the MgO substrate are achieved by initial growth of a Cr base layer at high temperature. Multiple superlattice diffraction peaks are observed in the low‐ and high‐angle x‐ray diffraction spectra. Three peaks are observed in the magnetoresistance associated with the oscillatory antiferromagnetic interlayer magnetic coupling as a function of Cr thickness. A maximum magnetoresistance of 150% at 4.2 K (28% at room temperature) is observed for a Cr(100 A)/[Fe(14 A)/Cr(8 A)]50 superlattice.

Magnetic decoupling in sputtered Fe/Si superlattices and multilayers

Sputtered Fe/Si superlattices were grown to study the magnetic coupling between ferromagnetic Fe layers (30 A thick) for Si spacer‐layer thicknesses (tSi) between 10 and 40 A. The material is ferromagnetical for tSi≤13 A and antiferromagnetically coupled for 13 A≤tSi≤17 A. For tSi≥17 A the Fe layers are uncoupled. X‐ray analysis indicates that the system is well layered, but that the crystal structure remains coherent only for tSi≤17 A. These results, along with our Mossbauer investigation, strongly suggest that the Si layer is crystalline for tSi≤17 A, and is silicide in nature. For thicker spacers, Si becomes amorphous. We propose a model of the layering that is consistent with the known properties of Fe silicide.

Magnetothermopower of Fe / Cr superlattices

Abstract We report magnetothermopower S(H) measurements at room temperature for sputtered [Fe(32 A) / Cr(x)]30 superlattices with x ≈ 5–50 A. The thermopower in zero field S(H = 0) appears to extrapolate to the known values for Fe and Cr in the x = 0 and large-x limits, respectively, and drops below these values at intermediate x. S follows the same trend with H and x as the magnetoresistance (MR), which shows oscillatory behavior as a function of x, and large field effects for antiferromagnetic Fe interlayer couplings. Both S(H) and the MR saturate when the applied field aligns the magnetization of the Fe-layers parallel to each other, but the thermopower is enhanced by application of a magnetic field, while the resistivity decreases, in accord with expectation.

Surface phonons in Cu/Ni superlattices

The modulation wavelength dependence of the surface‐wave velocity in Cu/Ni superlattices has been investigated using Brillouin scattering. It is the first compositionally modulated system to be studied by this technique and the first for which elastic properties have been determined by both ‘‘macroscopic’’ methods and Brillouin scattering. Contrary to the enhancements previously reported in the biaxial modulus and in the Young’s modulus, the modulus associated with the surface‐wave velocity shows no evidence of anomalous behavior.

Epitaxial growth of body‐centered‐cubic transition metal films and superlattices onto MgO (111), (011), and (001) substrates

We demonstrate epitaxial growth of the bcc transition metals Nb, Mo, Fe, and Cr via sputtering onto single crystal MgO substrates. The epitaxial growth orientations are (011), (112), and (001) when grown onto MgO (111), (011), and (001), respectively. Further, we demonstrate that, under appropriate growth conditions, superlattices of these materials (e.g., Fe/Cr, Fe/V, and Mo/V) can be grown with the same epitaxial order as the films.

Photo‐induced antiferromagnetic interlayer coupling in Fe superlattices with iron silicide spacers (invited)

Sputtered Fe/FeSi films possessing antiferromagnetic (AF) interlayer coupling at room temperature develop ferromagnetic remanence when cooled below 100 K, but the AF coupling can be restored at low temperature by exposure to visible light of sufficient intensity (≳10 mW/mm2). We attribute these effects to charge carriers in the FeSi spacer layer, which, when thermally or photogenerated, are capable of communicating spin information between the Fe layers.

New measurements of the elastic properties of composition modulated Cu-Ni thin films

Using a new ultrasonic method which relies on the measurement of the in‐phase and quadrature components of a continuous ultrasonic excitation as a function of position, we have measured the flexural modulus of composition modulated Cu‐Ni self‐supporting thin films. For some of the films, we have also observed the shear (Sz) modulus (allowing the calculation of the biaxial and Young’s moduli). No enhancement of these moduli was observed for composition wavelengths in the range of 17–40 A.

Properties of Ni/Nb magnetic/superconducting multilayers

We examine structural, magnetic, and superconducting properties of magnetic/superconducting Ni/Nb multilayers. The Ni(Nb) films are textured {111}({110}) and have smooth interfaces. The average moment of the Ni atoms in the structure drops by 80% from that of bulk Ni for 19 A thick Ni layers in proximity to 140 A thick Nb layers, and goes to zero for smaller Ni thicknesses. The Nb layer is not superconducting for thicknesses <100 A in the presence of a 19 A thick ferromagnetic Ni layer. The behavior of the superconducting critical temperature as a function of the superconducting layer thickness was fitted and an interfacial scattering parameter and scattering time for the paramagnetic Ni regime determined.

Magnetotransport studies of epitaxial Cr thin films

We report the results of transport measurements on epitaxial Cr thin films. The variation of TN (The Neel transition temperature) with respect to the film thickness is discussed in terms of the stress in the film. In addition, the temperature dependence of the magnetoresistance and Hall resistance for temperatures from 4 to 150 K are measured and discussed, with particular attention to the temperature dependence of the nonlinear portion of the Hall data.