Tunneling magnetoresistance (TMR) read sensor with a long diffusion path and ex-situ interfaces in a sense layer structure

A read sensor, comprising:

• a barrier layer sandwiched between a lower sensor stack and an upper sensor stack;
• the lower sensor stack comprising:
• a pinning layer;
• a keeper layer structure on the pinning layer;
• an antiparallel-coupling layer on the keeper layer structure;
• and
• a reference layer structure on the antiparallel-coupling layer;
• the upper sensor stack comprising:
• a sense layer structure that includes a first layer comprising CoFe formed on the barrier layer, a second layer consisting of CoFeB having a thickness of 2 to 4.8 nm and formed directly on the first layer and a third layer consisting of NiFe formed directly on the second layer, wherein the total thickness of the first sense layer and the second sense layer is large enough to form a sufficiently long diffusion path to trap Ni atoms thereby preventing Ni atoms from migrating from the third layer to the barrier layer;
• wherein the sense structure has a diffusion path (defined as the total thickness of the first and second sense layers) of at least 3.2 nm;
• and
• a cap layer structure on the sense layer structure.