Ferromagnet/Semiconductor Hybrid Structure
- Introduction
Ferromagnetic metal (FM) /semiconductor (SM) hybrid structures combine
the fields of magnetism and semiconductor physics. FM/SM junctions can
be used to inject a spin polarized current into the SM. Spin-injection
into semiconductor is a key to realize a spin-FET, in which the coherent
spin state is tuned by an electric field. On the other hand, the understanding
of magnetic properties in submicron-size becomes more and more important
for the developments of magnetic recording technology such as magnetic
random access memory (MRAM). However, measurements on individual micro-magnets
are not straightforward. Arrays of micro-magnets are usually measured by
commercial SQUID susceptometers. A fringing field induced local Hall effect
device has a sufficiently high sensitivity to measure the coercive field
of individual micro-magnets.
- Control of magnetization states in micro-structured ferromagnetic rings
An SEM picture of a fabricated sample is shown in Fig. 1. A cross-shape
is a semiconductor Hall device. A NiFe micro-structured ferromagnetic ring
is placed near the Hall cross to detect a fringe field. An external magnetic
field is applied in parallel to the semiconductor two dimensional electron
gas in order not to affect the Hall resistance. Figure 2 shows hysteresis
loops of the Hall resistance. An outer diameter of the rings is fixed to
be 2.0 µm, and an inner diameter is varied from 0 (Disk) to 1.6 µm in steps
of 0.4 µm. We have observed a systematic change in hysteresis loops by increasing
the inner diameter. For narrow rings, sharp transitions from so-called
"onion" to "vortex" state are observed. In rings with
smaller inner diameter, the transitions are broad and more complex. The
measured Hall resistance loops can be well reproduced by magnetization
curves obtained from numerical simulation.
Reference
"Investigation of Ferromagnetic Microstructures by Local Hall Effect
and Magnetic Force Microscopy"
J. Nitta, T. Schaepers, H. B. Heersche, T. Koga, Y. Sato and H. Takayanagi
Jpn. J. Appl. Phys. 41, 2497 (2002).
"Control of magnetization state in microstructured permalloy rings"
M. Steiner, and J. Nitta
Appl. Phys. Lett. 84 939 (2004)
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| Fig.1: SEM picture of local Hall Effect device. |
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| Fig. 2: Local Hall measurements of NiFe rings with 2 mm outer diameter.
The inner diameters of the rings are varied. A systematic change in hysteresis
loops is observed by increasing the inner diameter. |
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