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Initializing Single Domain States in Barberpole Magnetoresistive Sensors

IP.com Disclosure Number: IPCOM000089608D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Feng, JJ: AUTHOR

Abstract

Fig. 1A shows a fragmentary plan view, and Fig. 1B shows a fragmentary elevation view of a structure known as a barberpole (BP) magnetoresistive (MR) sensor. A substrate 10 is coated with a thin-film stripe 11 of NiFe 80:20 alloy comprising an MR sensor. Gold connecting leads 13 and 14 and gold shorting bars 15, which are diagonally aligned with stripe 11, are deposited upon stripe 11 with the leads 13 and 14 extending out across substrate 10 to connection pads (not shown). Normally, a steady DC current ("sense current" I) is maintained through stripe 11 for providing magnetoresistive sensing. Usually an MR stripe 11 will have its easy axis (EA) along its length. However, domains develop which may be antiparallel (opposed in direction) along the length of stripe 11.

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Initializing Single Domain States in Barberpole Magnetoresistive Sensors

Fig. 1A shows a fragmentary plan view, and Fig. 1B shows a fragmentary elevation view of a structure known as a barberpole (BP) magnetoresistive (MR) sensor. A substrate 10 is coated with a thin-film stripe 11 of NiFe 80:20 alloy comprising an MR sensor. Gold connecting leads 13 and 14 and gold shorting bars 15, which are diagonally aligned with stripe 11, are deposited upon stripe 11 with the leads 13 and 14 extending out across substrate 10 to connection pads (not shown). Normally, a steady DC current ("sense current" I) is maintained through stripe 11 for providing magnetoresistive sensing. Usually an MR stripe 11 will have its easy axis (EA) along its length. However, domains develop which may be antiparallel (opposed in direction) along the length of stripe 11. Such opposed or antiparallel domains tend to cause switching at odd times, producing Barkhausen noise, as they do not switch together as a single domain.

Optimal operation of a BP MR sensor requires having the MR in a single- domain state since a multi-domain state will have a reduced MR sensitivity and increased susceptibility to Barkhausen noise. Normally, this preferred single- domain state can be produced by applying a small longitudinal bias field or by incorporating some unidirectional anisotropy into the structure.

This article describes a simple, low-cost procedure for converting a multi- domain BP MR sensor into a single-domain state. This single-domain state will then be stable against sm...