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Magnetic Films for Hall Effect Devices Useful for Magnetic Recording Heads

IP.com Disclosure Number: IPCOM000085753D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 4 page(s) / 60K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+2]

Abstract

Large anomalous Hall effect coefficients have been reported in ferromagnetic amorphous Gd-Co alloys. [1]

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Magnetic Films for Hall Effect Devices Useful for Magnetic Recording Heads

Large anomalous Hall effect coefficients have been reported in ferromagnetic amorphous Gd-Co alloys. [1]

A Hall effect magnetic sensor is composed of a ternary amorphous alloy of the formula RMX where: R is a rare earth material, e.g., Gd. M is a magnetic 3d- transition metal, e.g., Fe, Co, Ni X is a metal such as Mo, Au, Cu, Cr. Ag.

Additional rare earth materials, R, which are suitable include Nd, Tb and Dy. Additional materials suitable for X include nonmagnetic metal of group VIII. The unique quality of such alloys is that they provide sensitive Hall devices which provide a large signal in a small magnetic field.

Characteristically, the approach to saturation has a linear portion as in a bubble material as shown in Fig. 1. The sensitivity (Hall coefficient) R(H) can be defined as: R(H) = V(H) over H(sat) t over i where H(sat) is the field required to saturate the sample, V(H) is the saturation Hall voltage, t is the film thickness and i is the current flowing through the device.

The polarity of the Hall voltage will reverse when a reverse magnetic field of sufficient magnitude is applied. In addition, square-loop behavior can also be obtained if the composition is close to a magnetic compensation point.

The perpendicular saturation field of a uniaxial perpendicular magnetic thin film is given by: [2]

(Image Omitted)

where t is the film thickness and l is a characteristic length parameter given by: l = 10 square root of AQ over 4 pi M(s) where Q is the ratio of the perpendicular anisotropy field to the demagnetizing field: Q = H(K) over 4 pi M(s) and A is the exchange stiffness. Low saturation fields can be obtained by using a thickness, t, which is comparable in magnitude to l. For example, if: l = t, H(sat) = 0.018(4 pi M(s)).

Taking l = t = 1000 Angstroms, Q = 1 and A = 10/-6/ erg./cm, the required 4 pi M(s) is:

(Image Omitted)

H(sat) = 18 G.

The required value of A can be obtained in CdCoX ternary systems, where X is a nonmagnetic element such as Au, Cu, Ag, Mo, Cr. Some X elements, e.g., Mo or Cr, lower the atomic moment of Co which in turn lowers V(Hall). For Hall detectors, high sensitivity can be obtained in system such as GdCoAu in which A can be adjusted without reducing V(H). Under optimum conditions, the sensitivity, R(H), in an alloy with V(H) = 10 m.v. is nearly 1/2 m.v./G.

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To show why these ternary amorphous alloys are superior to other Hall detector materials, a figure of merit of R(H)/Rho(ave) can be compared. For Co- Gd-Au the values are R(H) approx. 34 x 10/-8/ omega cm/gauss, rho(avg) approx. 136 x 10/-6/ Omega cm and R(H)/Rho(avg) approx. 25 x 10/-4/ C/-1/. This compares with 2 x 10/-4/ G/-1/ for InAs and 7x 10/-4/ G/-1/ for InSb, the two best known semiconductor Hall detectors. In addition, fabrication of amorphous Co-Cd-Au films is simpler than obtaining the stoichiometric 1/1 ration of In-Sb in a film. Magnetic Recor...