First order reversal curve Hall analysis of zero-field skyrmions on Pt/Co/Ta multilayers

Abstract

Magnetic skyrmions are non-trivial spin textures that resist external disturbances and are promising candidates for use in next generation spintronic devices. However, a major challenge in the realization of devices based on skyrmions is the stabilization of ordered arrangements of these spin textures under ambient temperature and zero applied field conditions. Multilayers of ferromagnetic materials (Co) interspersed with heavy metals with strong spin–orbit coupling (Pt and Ta), exhibit interesting properties, as the Dzyaloshinskii–Moriya interaction, which is an anti-symmetric exchange interaction that tilts the spins of neighboring layers, helps to stabilize skyrmions. In this work we study the formation and stabilization of magnetic skyrmions in Pt/Co/Ta films using a first order reversal curve (FORC) analysis, obtained from Hall effect measurements. The analysis of the FORC Hall diagrams was used to determine the intensity of the magnetic fields that should be applied to nucleate and stabilize skyrmions at remanence. Magnetic force microscopy images and micromagnetic simulations were compared to determine the correlation of the domain textures with the applied field and magnetic parameters of the multilayers.

Stabilization of Magnetic Skyrmions on Arrays of Self-Assembled Hexagonal Nanodomes for Magnetic Recording Applications

“…Finally, at the remanence after the application of a 90 mT H R , most of the individual skyrmions merge into large worm domains, in a similar configuration as the one observed in the demagnetized state of Figure c. As shown in previous works, , when a large density of skyrmions is nucleated by appropriate field reversal protocols in the continuous MLs, the skyrmions are stabilized by mutual repulsion once a large skyrmion density is present in the sample, what prevents the merging of skyrmions into large domains after reducing the field to zero. Figure g shows a magnified view of a periodic lattice with hexagonally ordered skyrmions with an average diameter of 100 nm and separated by 200 nm.…”

“…When a field of 70 mT is applied, the average skyrmion diameters decrease to 150 nm, and they again grow into large stripe domains at the remanence. In the previous work, we only obtained stable skyrmions at the remanence in films with thicker Co layers ( t Co = 1.7 nm) as a consequence of a change in the effective anisotropy of the MLs with increasing Co thickness. , …”

“…Isolated skyrmions have been also nucleated when strong out-of-plane magnetic fields have been applied , and stabilized at remanence when out-of-plane field sequences (that produce a specific irreversible magnetization process) have been applied . In the recent work, we used first-order reversal curve (FORC) Hall analysis to determine the necessary magnetic field to be applied to nucleate and stabilize skyrmions in Pt/Co/Ta MLs . Nucleation fields above 100 mT were applied to obtain skyrmions with an average diameter of 200 nm at remanence on continuous MLs.…”

Temperature-modulated magnetic skyrmion phases and transformations analysis from first-order reversal curve study

“…While previous works had identified the fracturing and annihilation process during the negative field sweep [35][36][37][38][47][48][49], the lack of analysis of the process associated with the positive field sweep can lead to incomplete descriptions of the peaks. One main contradiction is the process of stripe fracturing into multiple shorter segments or skyrmions that continues to occur even when the upper peak had been almost completely translated off the FORC diagram.…”

Material systems for FM-/AFM-coupled skyrmions in Co/Pt-based multilayers

“…In order to turn an idea into a realization, materials are needed that allow 10 nm skyrmions at room temperature with long life-times, and enable low-energy and fast transport properties. Thinking of a technological realization, ferromagnetic Co/Pt-based magnetic multilayers (MMLs) are a promising materials platform in various respects [13][14][15][16][17][18][19][20][21]. For example, the magnetization of Co is out-of-plane, the large spin-orbit interaction of Pt generates a sizable DMI and individual sub-100 nm skyrmions at room temperature have been found experimentally in various Co/Pt systems [22][23][24][25].…”