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Soft magnetic layers for low-field-detection magnetic sensors



William F. Egelhoff Jr., Robert McMichael, Cindi L. Dennis, Mark D. Stiles, Freemon Johnson, Alexander J. Shapiro, Brian B. Maranville, Cedric J. Powell


We have investigated a wide variety of soft magnetic layers as sense layers for magnetic-field sensors. We find that in thin-film form, some of these soft materials can have susceptibilities (?) approaching those of the corresponding bulk material. In general, the highest ? values occur in trilayer structures with a non-magnetic film separating two soft magnetic films. The alloy Ni77Fe14Cu5Mo4 of the mu-metal family is the softest thin-film material we have found, and we can achieve hard-axis ? values above 105 in trilayer structures. The hard axis is preferred for magnetic sensors due to its near-linear response. The major impediment we have found to using these very soft layers in low-field sensors is that the X value decreases by almost two orders of magnitude when the soft structure is incorporated in a standard spin valve or tunnel junction. The problem appears to be stiffening of the soft layer by the stray field from ripple in the pinned layer. A partial solution is found in the use of a synthetic antiferromagnetic as the pinned film. The antiferromagnetic alignment appears to have a canceling effect on the stray field.
Thin Solid Films


magnetic sensors pinning, synthetic antiferro-magnet


Egelhoff Jr., W. , McMichael, R. , Dennis, C. , Stiles, M. , Johnson, F. , Shapiro, A. , Maranville, B. and Powell, C. (2006), Soft magnetic layers for low-field-detection magnetic sensors, Thin Solid Films, [online], (Accessed June 16, 2024)


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Created May 17, 2006, Updated October 14, 2021