Magnetization process of a single chain of nanomagnets

We have investigated the magnetization reversal process of a single chain of identical nanomagnetic dots fabricated from 30 nm thick Ni 80Fe20. The structures consist of two 5 μm wide support wires bridged with a single chain of identical dots of diameter δ in the range 100-250 nm. For fields applied perpendicular to the single chain, we observed an unusual size dependent hysteretic behavior in the magnetoresistance curve at high field. This is due to the magnetostatic interaction arising from the proximity of the magnetic charges. We are able to deduce from a simple micromagnetic simulation that the reversal process in the chain of dots with δ=100nm is mediated by a collective process of nearly coherent spin rotation. The magnetotransport measurements along the chain reveal a complex magnetization reversal process in the chain of nanomagnets. © 2002 American Institute of Physics.

The inverse problem in magnetic force microscopy--inferring sample magnetization from MFM images.

Nanomagnetic structures have the potential to surpass silicon's scaling limitations both as elements in hybrid CMOS logic and as novel computational elements. Magnetic force microscopy (MFM) offers a convenient characterization technique for use in the design of such nanomagnetic structures. MFM measures the magnetic field and not the sample's magnetization. As such the question of the uniqueness of the relationship between an external magnetic field and a magnetization distribution is a relevant one. To study this problem we present a simple algorithm which searches for magnetization distributions consistent with an external magnetic field and solutions to the micromagnetic equations' qualitative features. The algorithm is not computationally intensive and is found to be effective for our test cases. On the basis of our results we propose a systematic approach for interpreting MFM measurements.