Tunnel junction sensor with a multilayer free-layer structure
AssigneeInternational Business Machines Corporation
InventorHardayal Singh Gill
Life of this patent
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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.
Claims26
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.
A method for fabricating a thin film tunnel junction sensor for sensing an external magnetic field comprising the steps of:
- 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.
A disk drive comprising:
- 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.
Dependencies are inferred from the claim text.