Micromagnetics of small size patterned exchange biased Permalloy film elements (invited)

Abstract

In this article, we present a study on the micromagnetics of exchange biased Permalloy films. Specifically, by combining magnetic force microscopy with micromagnetic modeling simulation, the magnetization reversal processes in exchange biased Permalloy films were studied. The bilayer films were lithographically patterned into micrometer scale rectangular elements. It is shown that the micromagnetic simulations accurately predict domain configurations during magnetization reversal of the exchange biased Permalloy film elements and provide detailed magnetization distributions and transient dynamic magnetization configurations that could not yet be obtained experimentally. The study found that, for both NiO/NiFe and FeMn/NiFe systems, the exchange bias field measured on individual patterned micrometer scale bilayer film elements can be significantly larger than that measured on the sheet film sample.

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)

“…The H EB in Py/MgO is accompanied by a large vertical shift in the magnetic moment, indicating the presence of a substantial number of pinned spins (discussed latter). Both H c and H EB are non-zero even at 400 K, further supporting that T b is above 400 K. In contrast to the present case, Dimitrov and coauthors [19] have reported that both H c and H EB are independent of temperature when Py is interfaced with non-magnetic MgO as compared with the strong temperature dependences measured when Py is interfaced with AFM layers [7][8][9][10][11]. Fig.…”

“…roughly half of the spins (50%) are strongly pinned. This percentage is much higher than the numbers (2-4%) usually observed for a typical FM/AFM interface [7][8][9][10][11]. Although the exact location of the spins has not been specified in this study, we would assume that they are the pinned spins are somehow linked to the very irregular shape of the grains in this particular sample.…”

“…The magnetic properties of Py have been extensively reported for the case where it is interfaced with anti-ferromagnetic (AFM) materials such as hematite [7], CoO [8], IrMn [9], FeMn [10] and NiO [11]. In addition, some preliminary studies have been reported [6] on the deposition of Py on MgO bulk wafers.…”

“…These results suggest that a large fraction of the spins are strongly pinned and that fields in excess of 7T are required to rotate them away from their originally fixed direction. H EB and training effect (TE) are fundamental magnetic coupling phenomenon, and they are usually observed [7][8][9][10][11] in mixed magnetic metallic systems, in which AFM and FM phases coexist. The TE is typically manifested as the reduction of the EB field (H EB ) upon progressive field cycling.…”

Reversal behavior of exchange-biased submicron dots

“…1,4 In this work we combine ferromagnetic dot arrays with an antiferromagnet (AF). [5][6][7][8] When such a system is cooled below the Néel temperature T N of the AF in a magnetic field H CF , the interaction at the FM/AF interface gives rise to the exchange bias (EB) effect, revealed as a shift of the hysteresis loop along the field axis. 9 Many models have been proposed to explain EB.…”