Method and apparatus for testing magnetic properties of magnetic media

A method of testing a magnetic medium, comprising:

• applying a magnetic field of a time-varying strength to a portion of the magnetic medium;
• directing a polarized optical beam towards the portion of the magnetic medium that is in the magnetic field, wherein the optical beam is reflected by a surface of the magnetic medium at a point of incidence in the magnetic field;
• moving the magnetic medium relative to the optical beam so as to cause the point of incidence to repeatedly traverse each of a plurality of sectors along a track on the surface of the magnetic medium, wherein the strength of the magnetic field is varied in synchronization with motion of the point of incidence along the track;
• obtaining a series of Kerr signal measurements of the reflected optical beam as the point of incidence repeatedly traverses the sectors, each Kerr signal measurement being associated with (1) a corresponding one of the sectors in which the point of incidence was when the Kerr signal measurement was obtained and (2) a corresponding strength of the magnetic field at the time when the Kerr signal measurement was obtained;
• and
• grouping the series of Kerr signal measurements into ensembles such that the Kerr signal measurements in an individual ensemble are all associated with the same one of the sectors;
• and
• determining at least one magnetic property of at least one of the sectors from the Kerr signal measurements in the corresponding ensemble.

Apparatus for testing a magnetic medium, comprising:

• means for applying a magnetic field of a time-varying strength to a portion of the magnetic medium;
• means for directing a polarized optical beam towards the portion of the magnetic medium that is in the magnetic field, wherein the optical beam is reflected by a surface of the magnetic medium at a point of incidence in the magnetic field;
• means for moving the magnetic medium relative to the optical beam so as to cause the point of incidence to repeatedly traverse each of a plurality of sectors along a track on the surface of the magnetic medium, wherein the means for applying the magnetic field and the means for moving the magnetic medium cooperate to vary the strength of the magnetic field in synchronization with motion of the point of incidence along the track;
• means for obtaining a series of Kerr signal measurements of the reflected optical beam as the point of incidence repeatedly traverses the sectors, each Kerr signal measurement being associated with (1) a corresponding one of the sectors in which the point of incidence was when the Kerr signal measurement was obtained and (2) a corresponding strength of the magnetic field at the time when the Kerr signal measurement was obtained;
• means for grouping the series of Kerr signal measurements into ensembles such that the Kerr signal measurements in an individual ensemble are all associated with the same one of the sectors;
• and
• means for determining at least one magnetic property of at least one of the sectors from the Kerr signal measurements in the corresponding ensemble.

Non-transitory computer-readable media containing instructions which, when executed by a computing device, cause the computing device to implement a method that comprises:

• receiving a time series of measurements, each measurement representative of a manifestation of a magneto-optic Kerr effect within an individual sector from among a plurality of sectors of a magnetic medium at an associated strength of an applied magnetic field, the measurements associated with different sectors being time-interleaved;
• grouping the time series of measurements into ensembles, the measurements in each one of the ensembles being associated with a respective one of the sectors;
• determining at least one magnetic property of plural ones of the sectors from measurements in the corresponding ones of the ensembles;
• and
• outputting an indication of said at least one magnetic property of said plural ones of the sectors.