by Professor Robert Stamps
Exceptional advances in the control of material properties has been achieved,
through careful manipulation of geometry on nano- and sub-nanometre length
scales, in magnetoelectronics and nanomagnetism.1
Advanced techniques now allow for the creation of structures patterned on
sub-micron length scales in three dimensions. New phenomena has been discovered
in patterned magnets that can be strongly controlled by ion bombardment,
multilayering, and lithographic patterning.
Examples include: materials for microwave signal processing technologies,
whose properties that can be tuned by magnetic and electric fields; high speed
switching of magnetization in elements used for data storage and spin
electronics; and manipulation of magnetic domains and domain walls in carefully
crafted structures that serve as model experimental systems for studies of
Figure 1. Array of
magnetic dots patterned from a Py film.
Perhaps the most famous example of how geometry can control fundamental
material properties is Bragg scattering of electrons in crystals. Most recently
an analogy has been created for microwave excitations in two dimensional
magnetic arrays, known as 'magnonic crystals'. These excitations can be
diffracted by magnetic features with appropriate dimensions.
An array of magnetic wires was constructed from a 30 nm thick
Ni80Fe20 film using deep ultraviolet lithography and
lift-off, forming a diffraction array for magnetostatic spinwaves. The magnetic
wires were 350 nm wide and spaced 55 nm apart A stop band was observed for
propagation perpendicular to the stripe axes, demonstrating the possibility of
engineering a magnonic band structure.2
Figure 2. Labyrinth
array formed by magnetic domain walls in a thin Co
A completely different type of dynamics can be controlled using patterning:
magnetic domain wall mobilities.3,4 A Co film bilayer (each film 0.6 nm thick)
was covered by an array of square Co dots created using ion beam etching.5 The function of the dots was to produce stray fields of
sufficient strength in the bilayer to affect domain wall motion. Significant
effects on wall mobility were observed, demonstrating for the first time that
domain wall motion can be controlled using simple, field controllable, magnetic
Some of the most exciting results in recent years have emerged from studies
of how conduction currents interact with magnetization. One result is that
conduction currents can cause magnetic domain boundary walls to move. The
physics can be understood simply in terms of reflection and transmission of
spins from the magnetic domain wall, which acts like a four point resistor in an
effective circuit model.6 A number of exciting new
applications are being explored for new logic schemes and data storage
1. R. E. Camley and R. L. Stamps, J. Phys.: Condensed Matter,
1993, 5, 3727
2. M. Kostylev, P. Schrader, R. L. Stamps, G.
Gubbiotti, G. Carlotti, A. O. Adeyeye, S. Goolaup, N. Singh, Appl. Phys. Lett.
2008, 92, 32504
3. M. Bauer, A. Mougin, J. P. Jamet, V.
Repain, J. Ferre, R. L. Stamps, H. Bernas, C. Chappert, Phys. Rev. Lett. 2005,
4. P. J. Metaxas, J. P. Jamet, A. Mougin, M.
Cormier, J. Ferre, V. Baltz, B. Rodmacq, B. Dieny, R, L. Stamps, Phys. Rev.
Lett., 2007, 99, 217208
5. P. J. Metaxas, P.-J. Zermatten,
J.-P. Jamet, J. Ferre, G. Gaudin, B. Rodmacq, A. Schuhl, R. L. Stamps, Appl.
Phys. Lett., 2009, 94, 132504
6. P. E. Falloon, R. A. Jalabert,
D. Weinmann, R. L. Stamps, Phys. Rev. B 2004, 70, 174424
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