Method for providing a self-pinned differential GMR sensor having a bias structure comprising layers of ferromagnetic and non-magnetic material selected to provide a net-zero magnetic moment
View Patent ↗A method for providing a self-pinned differential GMR sensor and self-pinned differential GMR sensor. The differential GMR head includes two self-pinned GMR sensors separated by a gap layer. The gap layer may act as a bias structure to provide antiparallel magnetizations for the first and second free layers without using an antiferromagnetic layer. The gap layer may include four NiFe ferromagnetic layers separated with three interlayers. The gap may also be formed to include a structure defined by Ta/Al 2 O 3 /NiFeCr/CuOx. One of the pinned layer may include three ferromagnetic layers so that the top ferromagnetic layer of the bottom pinned layer and the bottom ferromagnetic layer of the bottom pinned layer have a magnetization 180° out of phase. The self-pinned GMR sensors may include synthetic free layers that includes a first free sublayer, an interlayer and a second free sublayer that are biased 180° out of phase.
1. A method for forming a differential GMR sensor, comprising:
forming a first shield and first gap layer;
forming a first self-pinned GMR sensor having a first pinned layer, a first spacer layer and a first free layer;
forming a bias structure over the first free layer, wherein the bias structure comprises layers of ferromagnetic and non-magnetic material selected to provide a net-zero magnetic moment; and
forming a second self-pinned GMR sensor having a second pinned layer, a second spacer layer and a second free layer, wherein the bias structure is further formed to provide antiparallel magnetizations for the first and second free layers without using an antiferromagnetic layer;
wherein the forming the bias structure further comprises forming four ferromagnetic layers separated with three interlayers.
2. The method of claim 1 , wherein the forming four ferromagnetic layers separated with three interlayers further comprises forming four ferromagnetic layers separated with three interlayers selected to provide a desired gap length.
3. The method of claim 1 , wherein the forming four ferromagnetic layers separated with three interlayers further comprises forming three interlayers comprising ruthenium.
4. The method of claim 1 , wherein the forming four ferromagnetic layers further comprises forming four NiFe layers.
5. The method of claim 4 , wherein the forming four NiFe layers further comprises forming four NiFe layers having a nickel composition of 90%.