Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers

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.

Review Article: FePt heat assisted magnetic recording media

“…After deposition, the samples were processed by rapid thermal annealing (RTA) at 700 C for 30 s in N 2 atmosphere. It has been demonstrated that RTA processing of FePt/Cu bilayers does not only lead to chemical ordering but also to the development of a (001) texture on amorphous substrates, [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]68 which reveals the high potential of an RTA process for the fabrication of future FePt-based devices.…”

“…Recently, the magnetic reversal behavior in hard/soft bilayer thin-films with 90 coupling angle has been discussed. 51 Furthermore, heat assisted magnetic recording composite media, consisting of a superparamagnetic writing layer and a (doped) FePt storage layer, were proposed. 52 The advantages include reduced sensitivity to T C variance in the storage layer, and the opportunity to significantly lower the T C of the FePt storage layer without increasing the T C distributions, which adversely affect the recording performance.…”

Magnetization reversal in kagome artificial spin ice studied by first-order reversal curves

“…Such a "left-bending boomerang" feature 7 in the corresponding M-FORC distribution is typically associated with systems that exhibit domain nucleation and abrupt propagation [33], where domain growth is dominated by a strong exchange interaction [29]. Due to the presence of the exchange and dipolar interaction, the magnetization reversal in the spin-ice system usually takes place via DW nucleation from the sample edges, and propagate through the interconnections to form the Dirac strings [8,9,18].…”

“…shows a "left-bending boomerang" feature [33], which consists of a horizontal ridge for Hr >-330 Oe and a valley-peak pair for more negative Hr. Such a "left-bending boomerang" feature 7 in the corresponding M-FORC distribution is typically associated with systems that exhibit domain nucleation and abrupt propagation [33], where domain growth is dominated by a strong exchange interaction [29].…”

“…It provides information about irreversible magnetic switching [29,30], magnetic interactions [31][32][33], distributions of magnetic characteristics [34,35], and magnetic phase separation [36,37], which are not easily accessible in conventional hysteresis loop investigations. While most FORC studies have been based on magnetometry measurements (M-FORC), recently the FORC methodology has also been extended to transport measurements such as magnetoresistance curves (MR-FORC) to probe spin disorder [38], and temperature-dependent resistivity measurement to investigate first order phase transitions [39,40].…”