Tunnel junction sensor with a multilayer free-layer structure
First Claim
1. A thin film tunnel junction sensor for sensing an external magnetic field comprising:
- an antiferromagnetic layer;
a pinned ferromagnetic layer;
a barrier layer in contact with the pinned ferromagnetic layer; and
a free layer structure including;
a first layer of ferromagnetic material disposed adjacent to the barrier layer and having a first magnetostriction value which is positive and a first coercivity;
a second layer of ferromagnetic material having a second magnetostriction value which is negative and a second coercivity; and
a third layer of ferromagnetic material having a third magnetostriction value and a third coercivity, the third coercivity being lower than the second coercivity and the first, second and third magnetostriction values summing to approximately zero.
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Abstract
A tunnel junction sensor according to the invention replaces the prior art free layer with a free layer structure which allows a wider range of magnetoresistive materials to be used. The preferred free layer structure of the invention includes a negative magnetostriction layer which allows use of magnetoresistive materials which otherwise have unacceptably high magnetostriction values. The materials and thicknesses of the layers are selected to result in a total magnetostriction near zero even though magnetoresistive material with high magnetostriction is included. The preferred embodiment includes a softening layer of material such as selected compositions of nickel-iron which maintain the desired magnetic softness of the free layer structure and have a magnetostriction constant near zero.
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Citations
27 Claims
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1. A thin film tunnel junction sensor for sensing an external magnetic field comprising:
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an antiferromagnetic layer;
a pinned ferromagnetic layer;
a barrier layer in contact with the pinned ferromagnetic layer; and
a free layer structure including;
a first layer of ferromagnetic material disposed adjacent to the barrier layer and having a first magnetostriction value which is positive and a first coercivity;
a second layer of ferromagnetic material having a second magnetostriction value which is negative and a second coercivity; and
a third layer of ferromagnetic material having a third magnetostriction value and a third coercivity, the third coercivity being lower than the second coercivity and the first, second and third magnetostriction values summing to approximately zero. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for fabricating a thin film tunnel junction sensor for sensing an external magnetic field comprising the steps of:
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depositing an antiferromagnetic layer;
depositing a pinned ferromagnetic layer;
depositing a barrier layer in contact with the pinned ferromagnetic layer; and
depositing a free layer structure including;
a first layer of ferromagnetic material disposed adjacent to the barrier layer and having a first magnetostriction value which is positive and a first coercivity;
a second layer of ferromagnetic material having a second magnetostriction value which is negative and a second coercivity; and
a third layer of ferromagnetic material having a third magnetostriction value and a third coercivity, the third coercivity being lower than the second coercivity and the first, second and third magnetostriction values summing to approximately zero. - View Dependent Claims (15, 16, 17, 18, 20, 21)
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22. A disk drive comprising:
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a thin film disk including a thin film of ferromagnetic material on a planar surface of the disk;
a spindle rotatably supporting the disk; and
a tunnel junction magnetic sensor having an air bearing surface supported over the planar surface of the disk, the magnetic sensor including;
a antiferromagnetic layer;
a pinned layer;
a barrier layer adjacent to the pinned layer;
a magnetoresistive layer disposed adjacent to the barrier layer and having a first magnetostriction which is positive;
a negative magnetostriction layer disposed adjacent to the magnetoresistive layer and having a second magnetostriction which is negative; and
a softening ferromagnetic layer disposed adjacent to the negative magnetostriction layer, having a coercivity lower than a coercivity of the negative magnetostriction layer and having a third magnetostriction which results in approximately zero total magnetostriction when summed with the first and second magnetostriction. - View Dependent Claims (23, 24, 25, 26, 27)
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Specification