Plenarvorträge - DPG-Tagungen

Magnetismus Donnerstag
MA 26 Mikro- und nanostrukturierte Materialien
Zeit: Donnerstag 15:15–18:45 Raum: H10
MA 26.1 Do 15:15 H10
MAGNETIC PROPERTIES OF BULK AMORPHOUS Fe-
Cr-Mo-Ga-P-C-B ALLOYS — •Mihai Stoica 1 , Stefan Roth 1 ,
Jürgen Eckert 1,2 , and Ludwig Schultz 1 — 1 IFW Dresden, Institut
für Metallische Werkstoffe, Postfach 270016, D-01171 Dresden, Deutschland
— 2 TU Darmstadt, FG Physikalische Metallkunde, Petersenstrasse
23, D-64287 Darmstadt, Deutschland
The Fe65.5Cr4Mo4Ga4P12C5B5.5 bulk amorphous alloy exhibits good
soft magnetic properties. However, the maximum achievable diameter of
these Fe-based alloys is limited to only a few millimeters. Amorphous
rods with diameters of 1.5-3 mm and discs with 10 mm diameter and
1 mm thickness were prepared by copper mold casting. The coercivity
of as-cast rods and disc is around 5 A/m, decreasing up to less than 1
A/m upon annealing. The coercivity is expected to depend on the volume
fraction of crystalline inclusions. The saturation polarization is around
0.8 T and the magnetostriction constant λ = 9 ppm.
On the other hand, bulk amorphous samples with larger sizes or various
shapes can be prepared by powder metallurgical methods, i.e. mechanical
alloying or ball milling combined with subsequent consolidation of
the resulting powders. The aim of present work is to compare the magnetic
properties of as-cast amorphous samples obtained by copper mold
casting with samples prepared by hot pressing of ball milled melt-spun
ribbons.
MA 26.2 Do 15:30 H10
Domain observations in nanocrystalline ribbons — •Sybille Flohrer
1 , Rudolf Schäfer 1 , Ludwig Schultz 1 und Giselher Herzer
2 — 1 Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden,
P.O. Box 270016, D-01171 Dresden, Germany — 2 Vacuumschmelze
GmbH & Co. KG, Grüner Weg 37, D-63450 Hanau, Germany
Soft-magnetic nanocrystalline ribbons of the FeCuNbSiB type consist
of 10-15 nm wide crystalline grains of ferromagnetic FeSi, which are magnetically
coupled by a ferromagnetic metallic glass matrix. The exchange
coupling between the two magnetic phases leads to a seemingly uniform
magnetic material from the viewpoint of magnetic microstructure.
Kerr-microscopy observations on a variety of Fe73Cu1Nb3Si16B7 ribbons
treated under different conditions are presented. Magnetization
processes of annealed ring cores with strong and weak permeability are
compared, and the domains in ribbons with creep- and magnetizationinduced
anisotropy have been observed. Differences in the domain behavior
between high and low permeability material are explained in terms of
the random anisotropy model considering the ratio of average magnetocrystalline
and induced anisotropy.
MA 26.3 Do 15:45 H10
Nanocrystalline hard magnetic FePt powders — •Julia Lyubina
1 , Oliver Gutfleisch 1 , Nora M. Dempsey 2 , Axel Handstein
1 , Karl-Hartmut Müller 1 , and Ludwig Schultz 1 — 1 IFW
Dresden, P.O. Box 270016, D-01171 Dresden, Germany — 2 Laboratoire
Louis Neel, 25 Avenue des Martyrs, BP 166, 38042, Grenoble, France
The ordered FePt (L10) compound possesses high magnetocrystalline
anisotropy (K1 = 6.6 MJm −3 ) and saturation polarisation (Js = 1.43
T), as well as excellent mechanical properties and corrosion resistance.
Thus, it is a promising candidate for permanent magnet applications,
for instance in micro-electromechanical systems (MEMS). In the present
work we report on the preparation of nanocrystalline hard magnetic
Fe50+xPt50−x (x = 0; 5; 10.5) powders by mechanical milling at liquid
nitrogen temperature followed by annealing. The evolution of phase composition,
chemical order, and magnetic properties is studied as a function
of composition and annealing conditions. All the powders contain a mixture
of highly ordered L10 FePt (up to 90 vol. %), disordered FePt, as
well as Fe3Pt and FePt3 phases. The highest coercivity of µ0JHc = 0.7 T
was achieved in the Fe50Pt50 powder annealed at 450 0 C for 48 h, which
is substantially higher compared to that of conventional bulk FePt. The
microstructure of the annealed FePt powders has a lamellar character
with a typical grain size of about 40 nm. The coercivity increases with
increasing volume fraction of the L10 phase and degree of chemical order.
The authors are grateful to the DFG SFB 463 for financial support.
MA 26.4 Do 16:00 H10
Deep-submicron magnetic tunnel junctions patterned with
hydrogen silsesquioxane — •M. Krämer 1 , R. Adam 1 , A. van der
Hart 1 , H. Kohlstedt 2 , M. Weides 2 , H. Dassow 2 , and J. Schelten
1 — 1 Institut für Schichten und Grenzflächen, Forschungszentrum
Jülich GmbH, D-52425 Jülich — 2 Institut für Festkörperforschung,
Forschungszentrum Jülich GmbH, D-52425 Jülich
Nanostructuring of magnetic thin films is a necessary step in the investigation
of physical phenomena like single domain behaviour or superparamagnetism,
as well as, in the development of ultrasmall magnetic
tunnel junctions (MTJs) for high density magnetic memories. The aim
of our work is to fabricate magnetic tunnel junctions with lateral dimensions
far below one micrometer. To reach this goal a negative tone resist
based technique for the fabrication of deep-submicron magnetic tunnel
junctions using hydrogen silsesquioxane (HSQ) has been devised. HSQ is
an inorganic three dimensional polymer exhibiting SiO2-like properties
after annealing and was reported to behave as a negative e-beam resist
with a resolution better than 50 nm. This was used to pattern magnetic
trilayers into lines with a minimum width smaller than 60 nm connected
to external bonding pads. MTJs were then formed by placing a second
line across the first after edge isolation. Magnetoresistance measurements
performed on MTJs smaller than 100 nm are presented.
MA 26.5 Do 16:15 H10
Magnetic recording on nanostructures — •Manfred Albrecht 1 ,
Charles T. Rettner 2 , Andreas Moser 3 , Margaret E. Best 3 ,
and Bruce D. Terris 3 — 1 University of Konstanz, Dept. of Physics,
P.O.Box M631, D-78547 Konstanz, Germany — 2 IBM Almaden Research
Center, 650 Harry Road, San Jose, CA 95120, USA — 3 Hitachi San Jose
Research Center, 650 Harry Road, San Jose, CA 95120, USA
The creation of lithographic magnetic nanostructures for single-bit
data storage is recognized as a promising approach to overcoming the
areal density limit for magnetic recording imposed by superparamagnetism
[1].
Isolated tracks of magnetic single-domain nanostructures with lateral
sizes of up to 30 nm have been fabricated by patterning perpendicular
Co70Cr18Pt12 continuous films using focused ion beam lithography. We
demonstrate writing and reading of individual nanostructures using a
scanning magnetoresistive microscope. We present results on transition
position jitter and signal-to-noise ratio (SNR) for nanostructure arrays
and compare them with those on equivalent unpatterned strips of the media.
We observe that patterning dramatically reduces jitter and improves
SNR, which is independent of track width [2]. Moreover, the synchronization
requirements needed for writing bits in patterned media was
investigated and a novel type of magnetic pattern for servo control was
introduced [3].
[1] D. Weller and A. Moser, IEEE Trans. Magn. 35, 4423 (1999).
[2] M. Albrecht et al., Appl. Phys. Lett. 81, 2875 (2002).
[3] M. Albrecht et al., Appl. Phys. Lett. 83, (2003) in press.
MA 26.6 Do 16:30 H10
Lorentzmikroskopische Untersuchungen an Permalloy-
Kreisringen — •Thomas Uhlig, Christian Dietrich und Josef
Zweck — Institut für Experimentelle und Angewandte Physik,
Universität Regensburg, Universitätsstr. 31, 93053 Regensburg
Ringförmige magnetische Strukturen im µm-Bereich wurden in den
vergangenen Jahren verstärkt untersucht [1], da sie als potentielle Kandidaten
für die Verwirklichung magnetoresistiver Speicherelemente gelten
[2]. Die besondere Eignung folgt aus dem minimalen Streufeld und den
definierten Magnetisierung- und Schaltzuständen.
Durch den Einsatz der differentiellen Phasenkontrastmikroskopie
(DPC) [3] am Transmissionselektronenmikroskop kann sowohl die
Domänenkonfiguration als auch die Hysteresekurve eines einzelnen
Rings bestimmt werden. Durch gezielte geometrische Variationen an
den Proben lässt sich das Ummagnetisierungsverhalten beeinflussen.
Die dadurch veränderten Induktionskonfigurationen im Objekt können
simultan direkt beobachten werden.
[1] z.B. Rothman J., Kläui M., Lopez-Diaz L., Vaz C.A.F., Bleloch A.,
Bland J.A.C., Cui Z., Speaks R., Phys.Rev.Lett. 86, 6 (2001), 1098
[2] Zhu J.G., Zheng Y., Prinz G.A., J.Appl.Phys. 87 (2000), 6668
[3] Chapman J.N., Batson P.E., Waddell E.M., Ferrier R.P., Ultrami-