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Measurement of Magnetization or Magnetic Susceptibility of Small Particles and Measurement of Field Gradients of Domain Walls

IP.com Disclosure Number: IPCOM000040116D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Chiang, S: AUTHOR [+2]

Abstract

An instrument is described which (a) permits the force calibration of an Ultra-Small Force Probe (USFP) to enable it to measure the magnetic susceptibility of a single small particle and (b) enables an Atomic Force Microscope (AFM) to measure small-scale inhomogeneities of the magnetic field which occur on magnetic domain walls between domains of different magnetization orientation. This instrument comprises a needle having a fine tip firmly attached to an elastic medium, a small magnetic particle attached to the tip of the needle, a means for measuring very small displacements of the needle, means for producing a known magnetic field with a field gradient, and means such as piezoelectric drivers which can move the needle and its attached magnetic particle with respect to the magnetic field in very small calibrated steps.

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Measurement of Magnetization or Magnetic Susceptibility of Small Particles and Measurement of Field Gradients of Domain Walls

An instrument is described which (a) permits the force calibration of an Ultra- Small Force Probe (USFP) to enable it to measure the magnetic susceptibility of a single small particle and (b) enables an Atomic Force Microscope (AFM) to measure small-scale inhomogeneities of the magnetic field which occur on magnetic domain walls between domains of different magnetization orientation. This instrument comprises a needle having a fine tip firmly attached to an elastic medium, a small magnetic particle attached to the tip of the needle, a means for measuring very small displacements of the needle, means for producing a known magnetic field with a field gradient, and means such as piezoelectric drivers which can move the needle and its attached magnetic particle with respect to the magnetic field in very small calibrated steps. Alternatively, the needle may have a tip composed of a magnetic material or a material with sufficient magnetic susceptibility to generate a force between the needle tip and source of magnetic field gradient. The instrument may be fabricated by substituting a magnetic recording head for the sample in an AFM and replacing the AFM tip with one having high magnetic susceptibility or an attached magnetic particle. To calibrate, apply a variable current through the coil of the recording head; place the tip into the magnetic field produced by the head to cause the magnetic force between the tip and the head to deflect the lever on which the tip is mounted; and detect this deflection (e.g., by optical interference or a capacitance detector). The frequency of the variable current through the head will drive the resonant response of the magnetic force and through it the lever deflection signal which is used to measure the force between the tip and head. Because the field distribution of the recording head is well known, the instrument provides an absolute measurement of the force signal in the USFP and AFM. The instrument can then be used to measure the magnetic susceptibility of other small particles selectively placed onto the tip of the lever so that the force bet...