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Imaging Magnetic Domains with Nanometer Resolution

IP.com Disclosure Number: IPCOM000110050D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 6 page(s) / 198K

Publishing Venue

IBM

Related People

Alvarado, SF: AUTHOR

Abstract

A new technique is proposed to image magnetic domains on ferromagnetic thin films with nanometer lateral resolution. It is based on the observation of magneto-optical effects on metallic magnetic media by light excitation related to tunneling with the tip of a scanning tunneling microscope (STM). The tip of an STM can excite light emission with very high circular polarization in a ferromagnet. Additionally, the light also exhibits a linear polarization component which is oriented along the tip axis. The degree of polarization depends on the tunneling voltage as well as on the properties of the tip and sample. At least part of the circular polarization can be accounted for by magneto-optical effects (1,2).

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Imaging Magnetic Domains with Nanometer Resolution

       A new technique is proposed to image magnetic domains on
ferromagnetic thin films with nanometer lateral resolution.  It is
based on the observation of magneto-optical effects on metallic
magnetic media by light excitation related to tunneling with the tip
of a scanning tunneling microscope (STM).  The tip of an STM can
excite light emission with very high circular polarization in a
ferromagnet.  Additionally, the light also exhibits a linear
polarization component which is oriented along the tip axis.  The
degree of polarization depends on the tunneling voltage as well as on
the properties of the tip and sample.  At least part of the circular
polarization can be accounted for by magneto-optical effects (1,2).

      The resonant excitation of polarized light emission is proposed
as a probing technique to image the magnetic domains of magnetic
metals and alloys.  This approach is based on the magneto-optical
effects occurring with nanometer resolution through local excitation
of optical resonant surface modes at the tunneling junction formed
between the tip and a magnetic substrate in an STM environment.  The
set up used for the measurement of the degree of circular
polarization of the fluorescence is illustrated in Fig. 1.  A
tunneling junction is established between a tip 1, not necessarily of
magnetic material, and the sample under study, e.g., a metallic
magnetic thin film 2.  By choosing a convenient bias VT, resonant
light emission hw can be excited.  The light, monochromatized with
the aid of a filter 3, passes through a Pockel's cell 4 and then
through a linear polarizer 5.

      The intensities for + g/4 retardation, l+ and l-, are measured
by a photomultiplier 6.  The degree of circular polarization is
                                                     (1)

                            (Image Omitted)

Provided it is measured at a convenient photon energy, p(x,y) can be
related to the local magnetization M(x, y) along the observation
direction n by a relation of the type
                                                     (2)
where k is a constant.  Thus, the polarization should change sign
when the magnetization vector changes from parallell to antiparallel
as tip 1 passes across a domain wall 7.

      Fig. 2a shows measurements performed using a Ni tip and a
polycrystalline Ni sample.  The polarization of the emitted radiation
changes as a function of the tip position, even changing sign, in a
manner reminiscent of the magnetization profile accross a sample with
randomly oriented magnetic domains, as expected for the Ni sample
which was not purposely magnetized.  The polarization and the
intensity of the emitted light do not show any apparent correlation,
as shown in Fig. 2b.  This indicates that the polarizati...