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Scanning Microspot Kerr Looper for High-Coercivity Materials

IP.com Disclosure Number: IPCOM000104814D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Re, ME: AUTHOR [+2]

Abstract

Disclosed is a new scanning apparatus for measuring magnetic properties of high-coercivity materials, e.g., disk media, on a &mu.m scale. Current Kerr techniques for such materials require macroscopic samples, providing an average measure of the magnetic properties over a region. This article describes the first apparatus for making &mu.m-scale measurements of high-coercivity materials, allowing investigations of local variations in magnetic properties.

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Scanning Microspot Kerr Looper for High-Coercivity Materials

      Disclosed is a new scanning apparatus for measuring magnetic
properties of high-coercivity materials, e.g., disk media, on a &mu.m
scale.  Current Kerr techniques for such materials require
macroscopic samples, providing an average measure of the magnetic
properties over a region.  This article describes the first apparatus
for making &mu.m-scale measurements of high-coercivity materials,
allowing investigations of local variations in magnetic properties.

      Disk media can be studied on millimeter or larger areas by
means of VSM or standard Kerr techniques [1].  Current microscopic
Kerr methods require modulation of the sample magnetism at high speed
to allow lock-in detection of the changing polarization [2 ], which
is not feasible for high-coercivity materials due to the large fields
involved.  Since disk media are poorly understood on a microscopic
scale, it is essential to have a technique for observing magnetic
properties of media on a &mu.m scale.

      The key to studying high-coercivity media lies in modulating
the reflected light rather than the magnetization of the sample.    A
50 kHz (f) photoelastic modulator induces a large, 100 kHz  (2f)
variation in the output intensity seen by a silicon photodetector.
By detecting the 50 kHz component of the intensity signal with a
lock-in amplifier (LIA), and keeping the input intensity constant,
the LIA provides a DC signal corresponding to the light polarization,
and therefore the magnetization state of the sample [3].

      Fig. 1 shows a schematic of the apparatus as incorporated into
a modified Leitz microscope.  A stabilized He-Ne laser enters the
microscope through a side port designed for alternate illumination
sources.  By altering the position and angle of the beam at the
entrance to the microscope, the location and focused size of the spot
on the sample and in the back focal plane of the objective can be
adjusted for maximum signal.  The laser spot must enter the objective
off-axis in order to have a large angle of incidence arriving on the
sample, as is necessary for coupling by means of the longitudinal
Kerr effect.  A compensator is used to zero the ellipticity of the
r...