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Magnetic Thin Films and Devices: NSF CAREER AWARD
Task 1: Surface Morphology and Magnetic Structure
R.D. Gomez, University of Maryland, College Park, MD
GOAL: To correlate microstructure and
magnetic properties of Co on Si(100) as a
function of thickness.
APPROACH: A UHV-system with deposition
and in-situ scanned probe microscope
capability is used to make cobalt arrays
with thickness gradient at the pattern
edges. A novel in-situ shadow mask is
developed.
ACCOMPLISHMENTS:
• First atomically-resolved systematic
correlation of grain-size and thickness.
•First UHV-MFM observations of domain
boundaries at edge
PUBLICATIONS:
• UHV MFM/STM study of in situ structured Cobalt films on Si(001), M. Dreyer and R. D. Gomez, Joint MMM/Intermag 2001
Conference, submitted.
Magnetic Thin Films and Devices: NSF CAREER AWARD
Task 2: Spin Polarized Tunneling Microscopy
R.D. Gomez, University of Maryland, College Park, MD
GOAL: To develop a spin-dependent
scanning tunneling microscope (STM) to
investigate magnetic domains of spin
polarized samples.
APPROACH: Use standard STM with special
CrO2 coated tip, on 200 nm perpendicularly
magnetized NiFe (permalloy) sample. CrO2
is 100% spin polarized, Permalloy is 30%.
Correlate with magnetic structure obtained
using magnetic force microscope (MFM).
DIGRESSION: CONTRAST FORMATION
In general, tunneling current density is a product
of density of occupied and unoccupied states of the
tip and sample:
occ
unocc
J   tip ( EF )   sa m ( EF  eV )
If tip and sample are polarized:
 occ ( EF , )   unocc ( EF , )   occ ( EF , )   unocc ( EF  eV , )
tip
sa m
Or,
tip
sa m
J  , J   J  , J 
MILESTONE:
Successful coating of STM tip, using high
temp CrO3 decomposition on O2 reactor
chamber.
ACCOMPLISHMENT:
Successful imaging of domains in permalloy
using CrO2 tip, possibly first observation of
domains of NiFe using spin polarized probe.
STM with
CrO3 tip,
magnetic
contrast
AFM,
sample
texture
MFM,
magnetic
domains
PUBLICATION: Development of Spin Polarized Scanning Tunneling Microscopy for Magnetic Domain Imaging,
J. Flory, M. Dreyer, W. Egelhoff, T. Egelhoff and R.D. Gomez, in prep.
Magnetic Thin Films and Devices: NSF CAREER AWARD
Task 3: Patterned Sub-micron Structures
R.D. Gomez, University of Maryland, College Park, MD
GOAL: To understand the domain
configuration and switching characteristics
of epitaxially grown Cobalt/MgO.
APPROACH: Use MFM in the presence of
applied external field on patterned films
fabricated at Stanford University by Prof.
R.L. White and S. Ganesan.
RESULTS:
• MFM images show exclusive domain
configuration with shape and crystal
anisotropy easy axes are parallel (S1).
• MFM images show single and bidomain
stable configurations when shape and
crystal anisotropy axes are orthogonal
(S2).
• For S1, Hc ~ 2500 Oe, single domain
reversal.
•For S2, Hc ~ 1800 Oe, reversal via
single and intermediate bidomain
states.