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Magnetic Field Tunnel Sensor

IP.com Disclosure Number: IPCOM000086993D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Slonczewski, JC: AUTHOR

Abstract

A thin-film magnetic-tunneling sandwich is proposed to sense small fields for application in tape heads, bubble detectors, magnetic wands and the like.

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Magnetic Field Tunnel Sensor

A thin-film magnetic-tunneling sandwich is proposed to sense small fields for application in tape heads, bubble detectors, magnetic wands and the like.

The features of this device are: 1. Combination of a magnetically hard (permanent magnet) and a magnetically soft magnetic film in a tunneling sandwich. 2. Biasing of the soft layer by the permanent-magnet layer. 3. Combination of two soft crossed-axed films in a tunneling sandwich.

On pages 2328-2330 of this issue a phenomenon is described, according to which the tunneling current I for a given voltage between two ferromagnets depends on the relative angle Theta between the respective magnetic moments: I = I(o)(1 Epsilon cos Theta).

To provide for a variation of I in response to an ambient magnetic field H, it is only necessary that the two films respond differently, causing Theta to change. Three devices are suggested:

(a) Bipolar detector (Fig. 1). Here, one film is soft (e.g., permalloy), and the other is a permanent magnet (e.g., Co or RE(x)Co(1-x)). The films are thin enough so that stray-field interaction is zero. For H=O, the soft film is demagnetized and I=I(o). When a field H parallel to the permanent magnetization is applied in excess of whatever coercive and demagnetizing effects H(d) exist in the soft layer (circa 1 oersted), then it becomes magnetized and a current change Delta 1 = Epsilon I(o) Sgn H (or, equivalently, change of voltage at constant I) occurs. The sign of Delta I agrees with the sign of H (see hysteresis loop in Fig. 1).

(b) Self-biased detector (Fig. 2). The thickness-to-diameter ratio of the hard film is sufficient...