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Tip for Spin-Polarized Tunneling

IP.com Disclosure Number: IPCOM000040624D
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Allenspach, R: AUTHOR [+2]

Abstract

Increasing demand for storage devices with higher packing densities requires the use of smaller domain structures than employed in the present-day hard disk and bubble domain type memories. A lateral resolution in the nanometer range permitting information to be obtained on the magnetic domains as well as on the domain walls, i.e., on the changes of magnetization in real space, is achieved with a technique which benefits from the characteristics of the scanning tunneling microscope (STM). The main difficulty in using a usual ferromagnetic tip is that the magnetism is mostly carried by d-electrons, whereas the more extended s-wave functions carry the tunnel current. However, the latter are expected to have energy splitting which is too small to give good magnetic resolution.

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Tip for Spin-Polarized Tunneling

Increasing demand for storage devices with higher packing densities requires the use of smaller domain structures than employed in the present-day hard disk and bubble domain type memories. A lateral resolution in the nanometer range permitting information to be obtained on the magnetic domains as well as on the domain walls,
i.e., on the changes of magnetization in real space, is achieved with a technique which benefits from the characteristics of the scanning tunneling microscope (STM). The main difficulty in using a usual ferromagnetic tip is that the magnetism is mostly carried by d-electrons, whereas the more extended s-wave functions carry the tunnel current. However, the latter are expected to have energy splitting which is too small to give good magnetic resolution. This difficulty may be overcome by using an EuS or EuO magnetic filter on a W-tip at low temperatures, as proposed in [*]. To avoid the difficulties associated with cryogeny, this article proposes that the tip be made of a half-metallic ferromagnet, such as the Heusler alloys, NiMnSb or PtMnSb, or CrO2 which can be grown epitaxially on sapphire. These materials are characterized by a gap in the density of states, the conductivity being carried strictly by one spin direction. One anticipates polarization effects near 100%, and, in fact, effects greater than 50% have been measured in photoemission on NiMnSb. Reference "Spin-Polarized Tunneling Storage Device," IB...