Abstract
Magnetic interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations. Here we demonstrate an extremely sensitive magnetic yoking effect and tunable interactions in FePt based hard/soft bilayers mediated by the soft layer. Below the exchange length, a thin soft layer strongly exchange couples to the perpendicular moments of the hard layer; above the exchange length, just a few nanometers thicker, the soft layer moments turn in-plane and act to yoke the dipolar fields from the adjacent hard layer perpendicular domains. The evolution from exchange to dipolar-dominated interactions is experimentally captured by first-order reversal curves, the ΔM method, and polarized neutron reflectometry, and confirmed by micromagnetic simulations. These findings demonstrate an effective yoking approach to design and control magnetic interactions in wide varieties of magnetic nanostructures and devices.
Highlights
Assessing and controlling interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations, such as ultrahigh density magnetic recording,[1,2] exchange spring composites for permanent magnets,[3] artificially structured model systems of spin ice[4,5,6] and analog memory,[7] and magnetic quantum-dot cellular automata,[8,9,10] etc
Note that for the sample with tA1 = 2 nm, the hysteresis loops are very similar to those for the L10-FePt alone, suggesting that the A1 layer orientation is dominated by the L10 layer through exchange coupling; this is consistent with the A1-layer's exchange length of lex=3.9 nm.[21]
The M measurements and magnetic force microscopy (MFM) results suggest that the left- and right-bending first-order reversal curve (FORC)
Summary
Assessing and controlling interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations, such as ultrahigh density magnetic recording,[1,2] exchange spring composites for permanent magnets,[3] artificially structured model systems of spin ice[4,5,6] and analog memory,[7] and magnetic quantum-dot cellular automata,[8,9,10] etc. In the emerging heat-assisted magnetic recording (HAMR) technology that separates the recording process at elevated temperatures from the ambient temperature storage environment,[11,12] a critical issue is to tailor the various magnetic interactions in the media.[13,14,15] These interactions are often complicated and correlated, e.g., exchange interaction within each grain vs dipolar interactions across neighboring grains, which directly impact the media performance such as the thermal stability and switching field distribution Careful balance of these interactions, e.g., through the introduction of boron or oxides at grain boundaries,[16,17] has been essential to optimizing the media performance. These results demonstrate an effective yoking approach to tailor interactions in nanomagnetic building blocks for wide varieties of technological applications
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