EXPERIMENTAL-STUDY OF THE VALIDITY OF SIMPLE DESIGN RULES FOR THE BIASING OF SPIN-VALVE-TYPE GMR HEADS

From an analytical description of magnetic interactions combined with finite-element modelling, design rules for giant magnetoresistance (GM R) element can be derived, For some practical designs we arrive at the conditions t(p)M(S)(p) < t(f)M(S)(f) and t(p)M(S)(p) approximate to g amma hH(F). Here t(p), t(f), M-S(p) and M-S(f) are the layer thickness es and the saturation magnetizations of the pinned and the free layer, respectively; h is the element height, H-F is the ferromagnetic inter layer coupling and gamma accounts for the soft magnetic environment of the sensor. We have fabricated yoke-type GMR heads in an adapted desi gn conforming to these rules. The GMR elements were Ta/8 nm Ni80Fe20/2 .8 nm Cu/6 nm Ni80Fe20/10 nm FeMn/Ta. From finite-element calculations we find that for our heads gamma approximate to 2, which together wit h H-F = 6 Oe and h = 5 nm obeys the design rules. Measurements of thes e heads show that indeed the optimum bias state is obtained without us ing the integrated bias conductor to apply a d.c. bias current, Measur ements also show that the limiting factor for the head output in this case may no longer be the head efficiency (geometry), but the maximum driving amplitude (saturation) of the GMR element. This sheds new ligh t on the current discussion whether for application of spin-valve mate rials in thin-film heads, a yoke-type or a shielded-type design would be advantageous. (C) 1998 Elsevier Science S.A.