Bistability of magnetic states in Fe-Pd nanocap arrays

Abstract

Magnetic bistability between vortex and single domain states in nanostructures are of great interest from both fundamental and technological perspectives. In soft magnetic nanostructures, the transition from a uniform collinear magnetic state to a vortex state (or vice versa) induced by a magnetic field involves an energy barrier. If the thermal energy is large enough for overcoming this energy barrier, magnetic bistability with a hysteresis-free switching occurs between the two magnetic states. In this work, we tune this energy barrier by tailoring the composition of FePd alloys, which were deposited onto self-assembled particle arrays forming magnetic vortex structures on top of the particles. The bifurcation temperature, where a hysteresis-free transition occurs, was extracted from the temperature dependence of the annihilation and nucleation field which increases almost linearly with Fe content of the magnetic alloy. This study provides insights into the magnetization reversal process associated with magnetic bistability, which allows adjusting the bifurcation temperature range by the material properties of the nanosystem.

Size-dependent bistability of magnetic states in soft magnetic cap arrays

“…Both Fe 17 Pd 83 and Fe 15 Ni 85 cap arrays supported a magnetic vortex spin configuration at zero magnetic field in a wide temperature range. As Fe 15 Ni 85 is exhibiting higher values of T C and M S , an increase in the energy barrier e D is expected [19], shifting the bifurcation temperature in Fe 15 Ni 85 samples to near room temperature, as evidenced from figure 6. We also compare the calculated magnetostatic energy density with the observed bifurcation temperature for the two material systems.…”

“…Comparing with flat disk, caps reverse with smaller nucleation/annihilation fields, which is attributed to the change in demagnetization energy [13]. As recently demonstrated, a hysteresis-free transition between the collinear state and the vortex state or vice versa is possible with the control of temperature [18,19]. By increasing the temperature of the system, the thermal energy can overcome the energy barrier involved.…”

“…In this bistable region, thermal fluctuations alone are sufficient to initiate the switching process. In our previous work [19], we have demonstrated that for a fixed diameter and thickness of the magnetic caps consisting of a soft magnetic Fe-Pd alloy, magnetic bistability can be controlled by tuning the composition of the alloy thin film. Specifically, as the Fe content in the Fe-Pd alloy was increased from 13 to 20 at%, both the saturation magnetization M S and the Curie temperature T C of the Fe-Pd alloy increased as well, resulting in a rise of the energy barrier for the switching from a collinear to a vortex state (or vice versa).…”

“…In dense arrays of planar disks, the magnetization reversal of vortices can be tuned by altering the magnetic dipolar inter-disk coupling [7,8]. Furthermore, vortex states can also be achieved by magnetic film deposition onto particle arrays where different aspects of magnetic reversal were investigated [10][11][12][13][14][15]19]. In addition, in these cap structures, the curvature can also affect the critical fields, where the thickness gradient plays a more dominant role in the reversal mechanism.…”

Dependence of the Magnetization Process on the Thickness of Fe70Pd30 Nanostructured Thin Film

“…The combination of magnetic and martensitic order makes this metallic multiferroic material a promising candidate for applications in micro-and nanodevices [10]. Recently, Fe-Pd alloy nanostructure arrays based on self-assembling techniques have shown a strong potential for energy-assisted recording on nanoscale magnetic media, ultrafast spintronic technology and nano-actuators in biomedical applications [11][12][13][14]. For such applications, tailoring the direction and strength of the magnetic anisotropy, especially for the thermal stability and switching reliability of magnetic bits, is a crucial prerequisite [15].…”