MAGNETIC THIN FILMS & TAILORED PERMANENT MAGNETS

The Magnetic Films Group focuses on the preparation and characterization of ultrathin metallic films, including novel epitaxial overlayers, wedges, sandwiches, and superlattices. Scientific challenges range from creating atomically-engineered materials with new properties, to utilizing new techniques to characterize structure-property relationships. Current focus is on magnetic coupled-layer phenomena associated with giant magnetoresistance (GMR) and hard magnet effects, as well as growth, morphology, phase stability, anisotropy, phase transitions and critical behavior, and related low dimensional magnetic effects.

Among major accomplishments of this program is the realization of record-setting GMR values for epitaxial, sputtered Fe/Cr superlattices (Fig. 1 and 2), and the introduction of the surface magneto-optic Kerr effect (SMOKE) to study surface magnetism (Fig. 3).













magfig1.gif
Fig. 1. 150% GMR for Fe/Cr(100) superlattice at 4.2 K.

Capabilities

Growth of ferromagnetic monolayers, ultrathin epitaxial wedges and superlattices, and high-coercivity rare-earth-transition-metal films via molecular beam epitaxy (MBE) and sputtering techniques.

Thin-film and surface-science characterization techniques, including x-ray and electron diffraction (LEED and RHEED) and neutron scattering analysis.

Electronic properties analysis via Auger and spin-polarized photo-emission, band-structure theory, and low-temperature transport, magnetic and magneto-optic Kerr effect measurements.

Analysis of elastic, magnetic, and vibrational properties using Brillouin and Raman scattering.





magfig2.jpg
Fig. 2. Eric Fullerton positions a GMR sample in the poles of a magnet for magneto-optic studies.

Applications

Design of new permanent magnets for applications with improved corrosion resistance and lower material costs.

The GMR effect makes possible new magnetoresistive sensors and magnetic-recording read heads.

Major Resources

Ultrahigh vacuum SMOKE surface-science chamber with 2-Tesla superconducting magnet.

Magnetron sputtering and MBE chambers with in-situ surface analysis capabilities.

High-field, variable-temperature magnetometers (7 and 9-Tesla).

Brillouin light scattering tandem Fabry-Perot interferometer.

Raman spectrometer.

Diamond-anvil high-pressure cell.

Magneto-optic Kerr spectrometer.

Spin-polarized photoemission undulator beamline at NSLS.

magfig3.jpg
Fig. 3. SMOKE chamber.

Selected Accomplishments

 

SMOKE Studies of MBE Wedges.
The SMOKE technique was pioneered for in-situ magnetic characterizations.

A new magnetic phase diagram was proposed for ultrathin face-centered phases of Fe grown epitaxially on Cu(100).

Coupled magnetic layer phenomena were studied for Fe/Mo(wedge)/Fe(100) and Co/Cu(wedge)/Co(100).

The two-dimensional spin-reorientation transition was studied for Fe/Ag(100).






magfig4.jpg
Fig. 4. Fe(wedge)/Ag(100) spin-reorientation transition
via polar ( ^ ) and longitudinal ( §§ ) SMOKE.

 

Spin-Polarized Photoemission

Magnetic quantum well behavior identified the Fermi-surface caliper responsible for the oscillatory coupling in Fe/Cr GMR materials.

Sputtered Fe/Cr Superlattices

Comprehensive studies of Fe/Cr superlattices - including, crystal lographic orientational and temperature dependencies of GMR, oscillatory and biquadratic couplings, and role of Cr Néel transition and spin-density-wave antiferromagnetism.

First experimental realization of the surface spin-flop transition.

Light Scattering

First observation of quantum confinement of phonons in a metallic multilayer system - for Ru Raman modes in Co/Ru.

Use of ruby luminescence of alumina-forming steels to show that reactive element (Hf, Zr) produces scales which can sustain high strains prior to spallation.

Tailored Permanent Magnets

Growth procedures and seed layers have been optimized for the sputter-growth of epitaxial Sm-Fe and Nd-Fe hard-magnet films.

Ultrahigh vacuum evaporation of ultrathin (>30 nm) Nd-Fe-B exhibit bulk-like coercivities and spin-reorientation transition.

Initiating efforts to exchange harden via interleaving hard and soft layers to reduce rare-earth content and boost energy product.

Fig. 5. Hysteresis loop for Nd-Fe-B film at room-temperature and 20K.

New Directions
A colossal magnetoresistance (CMR) of 5,700% was observed at the metal-insulator transition of the naturally layered manganite La 1.2 Sr 1.8 Mn 2 O 7 .

Superconducting / Ferromagnetic (S/F) multilayers are under study to identify new magnetic behavior associated with the interplay of the two phenomena.

Collaborations

Within the Materials Science Division.

Within Argonne, especially at the Intense Pulsed Neutron Source and the Advanced Photon Source.

At major DOE facilities, such as at Brookhaven's synchrotron (NSLS) and the Oak Ridge neutron scattering facility.

Within the DOE Center for Synthesis and Processing.

Within industrial CRADA relationships.

With university faculty and students, including via sabbatical and exchange programs.

Selected Publications

A General Approach to the Epitaxial Growth of Rare-Earth-Transition-Metal Films, E. E. Fullerton, C. H. Sowers, J. E. Pearson, X. Z. Wu, D. Lederman, and S. D. Bader, Appl. Phys. Lett. 69, 2438 (1996).

Confined Phonons in Metallic Superlattices: Raman Study of Co/Ru, M. Grimsditch, J. E. Mattson, C.H. Sowers, S. D. Bader, and M. J. Peters, Phys. Rev. Lett. 77, 2025 (1996).

Spin-density-wave Antiferro-magnetism of Cr in Fe/Cr(001) Superlattices, E. E. Fullerton, S. D. Bader, and J. L. Robertson, Phys. Rev. Lett. 77, 1382 (1996).

Magnetic Phases of Ultrathin Fe Grown on Cu(100) as Epitaxial Wedges, D. Li, M. Freitag, J. Pearson, Z. Q. Qiu and S. D. Bader Phys. Rev. Lett. 72, 3112 (1994).

Awards

S.D. Bader - University of Chicago Award for Distinguished Performance at Argonne National Lab, 1994.

Z. Q. Qiu, J. Pearson, and S. D. Bader - DOE / Basic Energy Sciences - Materials Sciences Award for Outstanding Scientific Accomplishment in Solid State Physics for work on Coupled Magnetic Layers, 1992.

Point of Contact

Samuel D. Bader
Phone: (630) 252-4960
Fax: (630) 252-9595
e-mail: Bader@ANL.GOV