Study of domain formation in small permalloy magnetoresistive elements

Our past work has shown that the Barkhausen noise in the transverse response of small (10–100 μm) permalloy MR sensors originates from domain wall activities; namely, the systematic creation, intensification, and wall-state transition of buckling domain structures. The cause and details of domain formation, however, remain unresolved. In this work, through direct domain observations and wall population studies, we will show that magnetostatic energy effects constitute the most basic cause of domain formation. Easy-axis dispersion (δK) effects can also cause domains, but primarily for the shorter elements. Also, we will show how the magnetic configurations along the top and bottom edges of the element affect the geometry of the resultant buckling domains, and how fluctuations in these edge configurations produce fluctuations in the domain geometry and, consequently, in the MR response. Finally, we will show that domain activities are not suppressed by different orientations of the easy axis, although interesting changes in the domain behavior may be produced.