(a)
(b)
(c)
O. Fruchart(a), F.
Cheynis(a), N. Rougemaille(a),
R. Belkhou(b,c),
J. C. Toussaint(a,d)
(a)Institut NÉEL, CNRS &
Université Joseph Fourier, Grenoble, France
(b)Synchrotron Soleil,
Saint-Aubin, Gif-sur-Yvette, France
(c)ELETTRA-Sincrotrone
Trieste, Basovizza, Trieste, Italy
(d)Institut National
Polytechnique de Grenoble, France
|
(a) |
|
|
(b) |
|
|
(c) |
|
|
FIG. 1: (a) AFM image of a typical Fe(110) faceted dot (length 1.65mm, height 180nm). (b) LEEM and (c) XMCD-PEEM images of the same dot, the latter revealing the Néel cap (here as a black line). |
An increasing
number of studies focus on magnetic domain walls (DW’s)
as objects that can be displaced by a magnetic field or a spin-polarized
current. The few reports on the manipulation of the internal configuration of
DW’s or vortices in nanostructures concern the reversal of
vortex cores in circular permalloy
dots [1-3]. These studies proved that two degrees of freedom can be manipulated
independently in the so-called vortex state: 1. the in-plane
chirality of magnetization; 2. the perpendicular
polarization of the vortex core. Here we go one step further and demonstrate
the manipulation of a third degree of freedom in a flux-closure state. We could
switch the direction of magnetization of Néel caps (NC's) occurring atop the
Bloch wall in elongated dots. Micron-sized self-assembled Fe(110)
dots grown by Pulsed Laser Deposition under UHV have been used as a model
system for this purpose [4] (Fig. 1).
|
|
|
|
(a) |
(b) |
|
Fig. 2:
Micromagnetic simulations. (a) Hysteresis under a magnetic field applied
transverse to the dot. Only the transverse component of the magnetization is
shown, highlighting the NC’s. (b) Schematic
illustration of how the set of Néel caps, antiparallel
at remanence, can be reversed depending on the sign of the applied field. |
The statistics of
switching of NC's following the application of a transverse
field has been
observed over tens of dots of mean height 100nm, using the XMCD-PEEM magnetic
microscopy setup of the Nanospectroscopy
beamline at Elettra (Italy) [5-6] (Fig. 1b-c).
Over 95% of NC’s have been switched at 150mT, with a mean reversal field of 125mT.
This result is confirmed quantitatively by micromagnetic
simulations
(Fig. 2). The simulations predict that the switching field reaches a
maximum for a height of 90nm, cancels around 20nm on the lower side, and slowly
decreases for larger thicknesses (Fig. 3). This dependence may be
used experimentally to tailor the value of the switching field.
|
Fig. 3: Dependence of the switching field of Néel
caps versus the thickness of the dot (Micromagnetic simulations). |
[1] T.
Okuno et al., J. Magn.
Magn.
Mater., 240,
1-6 (2002).
[2]
A. Thiaville et al., Phys. Rev. B, 67,
094410 (2003).
[3] B. Van
Waeyenberg et al., Nature, 444, 461-464
(2006).
[4] P.-O.
Jubert et al., Phys. Rev. B, 64, 115419
(2001); O. Fruchart et al., J. Phys.: Condens.
Matter, Topical review, 19,
053001(2007).
[5] F. Cheynis et al., J.
Appl. Phys. 103, 07D915 (2008)
[6] F. Cheynis et al., arXiv:0712.3834v1
