A two-step etching and deposition process is presented for making nanoscale exchange-biased NiFe/IrMn disks, and their magnetic properties are described as a function of diameter and thickness. The exchange bias in nanodots with diameters of 100–500 nm was reduced and the coercivity enhanced compared to the continuous film. Etching of the NiFe film prior to depositing the IrMn lowered the exchange bias; and the exchange bias also decreased as dot diameter decreased. The results are interpreted in terms of the relation between dot size and the antiferromagnetic domain size in the IrMn. The two-step process will be useful in introducing exchange bias at local regions of a ferromagnetic film.

We present a measurement of the B 0 →Λpπ − branching fraction performed using the BABAR detector at the PEP-II asymmetric energy e + e − collider. Based on a 232 million BB pairs data sample we measure: B(B 0 →Λpπ − ) = [3.30 ± 0.53 (stat.) ± 0.31 (syst.)] × 10 −6 . A measurement of the differential spectrum as a function of the di-baryon invariant mass m(Λp) is also presented; this shows a near-threshold enhancement similar to that observed in other baryonic B decays.

The magnetic switching behavior in continuous NiFe films patterned with IrMn gratings is investigated experimentally and with micromagnetic simulations. The samples made by a two-step deposition process consist of a 10-nm-thick NiFe layer on which is placed 10-nm-thick IrMn stripes with width from 100 to 500 nm and period from 240 nm to 1 μm. Exchange bias is introduced by field cooling in directions parallel or perpendicular to the IrMn stripes. The samples display a two-step hysteresis loop for higher stripe width and period, as the pinned and unpinned regions of the NiFe reverse independently but a one-step loop for lower stripe periods. The transition between these regimes is reproduced by micromagnetic modeling.

The magnetic reversal behavior is examined for exchange-biased ferromagnetic/antiferromagnetic nanostructures consisting of an array of 10 nm thick Ni80Fe20 stripes with width 200 nm and periodicity 400 nm, underneath an orthogonal array of 10 nm thick IrMn stripes with width ranging from 200 nm to 500 nm and periodicity from 400 nm to 1 μm. The Ni80Fe20 stripes show a hysteresis loop with one step when the IrMn width and spacing are small. However, upon increasing the IrMn width and spacing, the hysteresis loops showed two steps as the pinned and unpinned sections of the Ni80Fe20 stripes switch at different fields. Micromagnetic modeling reveals the influence of geometry on the reversal behavior.