Magnetic Resonance Force Microscopy
Towards Three-Dimensional Sub-Surface Atomic-Scale
Imaging of Magnetic Materials.
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H A M M E L
G R O U P Los Alamos
R O U
K E S G R O U P Caltech
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P. Chris Hammel
Condensed Matter and Thermal Physics
MS K764, Los Alamos National Laboratory,
Los Alamos, NM 87545 USA
Contact: Chris
Hammel + 505 665 0759
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Michael L. Roukes
Condensed Matter Physics,
Caltech 114-36,
Pasadena CA 91125 USA
Contact: Michael Roukes
+ 626 395 2933
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The magnetic resonance force microscope
(MRFM) is a novel scanned probe instrument which combines the three-dimensional
imaging capabilities of magnetic resonance imaging with the high sensitivity
and resolution of atomic force microscopy. It will enable non-destructive,
chemical-specific, high-resolution microscopic studies and imaging of subsurface
properties of a broad range of materials. This technology holds clear potential
for atomic-scale resolution.
New magnetic materials and devices with unprecedented
capabilities and levels of performance are now being created by tailoring
the structure and composition of multi-component materials at the nanometer
scale. The buried interfaces between the various components of these new
materials play a central role in determining their functional behavior.
We are presently applying the emerging capabilities of the MRFM to the
study of layered magnetoelectronic materials. The MRFM will enable very
high resolution studies of the structural and magnetic properties of the
buried interfaces.
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| High
Resolution Force Detected Magnetic Resonance Imaging |
Force Detection of
Magnetic Resonance
The magnetic resonance force microscope (MRFM) is a microscopic imaging
instrument that mechanically detects magnetic resonance signals by sensitively
measuring the force F=m·ÑB
between
a permanent magnet that provides ÑB,
and the spin magnetization m. Periodically modulating this force
by modulating m alters the oscillation amplitude of a high Q, low
spring-constant micro-mechanical resonator (cantilever or bridge) such
as is used presently in AFM.
High Resolution Magnetic
Resonance Imaging
The magnetic field gradient of the small magnetic tip serves a second key
role: it defines the spins (electronic or nuclear) which will be probed
in the magnetic resonance experiment. The resonance frequency of a spin
is proportional to the magnetic field it experiences:
w=gB(r),
only the resonant spins are effected by the magnetic resonance experiment.
As in conventional magnetic resonance imaging (MRI) the spatial variation
of B allows us to probe only those spins whose resonance frequency matches
the frequency wo of the applied rf
field, that is those spins residing in the "sensitive slice." |
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Magnetic
Multilayer Materials
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High sensitivity
magnetic field detectors for high density magnetic information storage
devices.
The field of magnetoelectronics is experiencing a huge resurgence of interest
and a new influx of research effort. The driving force is the technological
quest of the $100B/yr magnetic recording industry for increased storage
density in recording media. Further impetus also comes from the semiconductor
industry, in the area of memory: ideal non-volatile memory elements are
sought that can be produced, and addressed, in massive arrays. The
growth of high quality magnetic multilayer materials is providing the foundation
for a range of important modern advances in both fields, and offers
a new range of possibilities. The quality of such materials, upon which
the performance of these devices so strongly depends, is affected not only
by the purity of the materials grown, but, crucially, by the properties
of the interfaces between different layers. For example,
in magnetic multilayer materials displaying "giant'' magnetoresistance
(GMR), device performance is critically dependent on the microscopic characteristics
of the buried interfaces. GMR-based read heads have enabled up to
a 50% increase in magnetic storage density and have thus become a central
new technology for the industry. A second example is the recently developed
spin injection devices, which offer a new approach to non-volatile magnetic
memory. Although the physics of these new types of magnetic
systems is highly dependent upon interfacial characteristics, remarkably
little is known about the microscopic morphology of these interfaces.
Nor are the microscopic mechanisms that determine interfacial magnetic
properties well understood. MRFM studies will enable unprecedented
understanding of structural and magnetic properties of buried interfaces
and microstructure; this will enable development of materials with improved
properties. |
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Ferromagnetic
Resonance Using MRFM
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We have been performing MRFM detected FMR as a microscopic
probe of magnetic thin film materials. MRFM can enable microscopic characterization
of magnetic homogeneity and interlayer exchange coupling. Please see some of our
recent publications.
"Imaging mechanisms of force detected FMR microscopy"
J. Appl. Phys., 87, 6493 (2000)
(LAUR 00-2495)
"Observation of Ferromagnetic Resonance in a Microscopic
Sample Using Magnetic Resonance Force Microscopy"
Appl. Phys. Lett. 68, 2005 (1996)
(LAUR-95-3828)
"Ferromagnetic Resonance Force Microscopy on Microscopic
Co Single Layer Films,"
Appl. Phys. Lett. 73, 2036 (1998)
(LAUR-97-5168)
"Ferromagnetic Resonance Imaging of Co Films Using
Magnetic Resonance Force Microscopy"
J. Vac. Sci. Tech. B 16, 2275 (1998)
(LAUR-98-227)
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