Observation of a Chirality-Induced Exchange-Bias Effect

Abstract

Chiral magnetism that manifests in the existence of skyrmions or chiral domain walls offers an alternative way for creating anisotropies in magnetic materials that might have large potential for application in future spintronic devices. Here we show experimental evidence for an alternative type of in-plane exchange-bias effect present at room temperature that is created from a chiral 90 • domain wall at the interface of a ferrimagnetic-ferromagnetic Dy-Co/Ni-Fe bilayer system. The chiral interfacial domain wall forms due to the exchange coupling of Ni-Fe and Dy-Co at the interface and the presence of Dzyaloshinskii-Moriya interaction in the Dy-Co layer. As a consequence of the preferred chirality of the interfacial domain wall, the sign of the exchange-bias effect can be reversed by changing the perpendicular orientation of the Dy-Co magnetization. The chirality-created tunable exchange bias in Dy-Co/Ni-Fe is very robust against high in-plane magnetic fields (μ 0 H ≤ 6 T) and does not show any aging effects. Therefore, it overcomes the limitations of conventional exchange-bias systems.

Observation of compact ferrimagnetic skyrmions in DyCo$_3$ film

“…3f). Considering an exchange stiffness of A=6 pJ/m [50] and an effective anisotropy of K ef f =2.5 × 10 4 J/m 3 , the DMI constant is estimated to be in the range of 0.25-0.35 mJ/m 2 , which is in good agreement with the value of 0.18 mJ/m 2 determined for a 70 nm-thick DyCo 4 film [48]. The domain wall width can be calculated to be w = π A/K ef f = 49 nm, which is also in agreement to the value of 50 nm obtained from the skyrmion profile (Fig.…”

“…Ferrimagnetic systems may open an alternative route towards the realization of skyrmion systems suitable for applications. Particularly, ferrimagnetic films of amorphous alloys consisting of 4f rare-earth and 3d transition-metal elements (RE-TM alloys) exhibiting perpendicular magnetic anisotropy are attracting very much attention because of their versatile magnetic properties [43][44][45][46][47][48][49][50]. First realizations of skyrmions in ferrimagnetic RE-TM alloys were reported only recently, e.g., showing a promising reduction of the SkHE [51] or even a complete suppression of the SkHE at the angular momentum compensation temperature [52].…”

“…Notably, the absence of a center of inversion symmetry in amorphous materials inherently causes a non-vanishing DMI [57]. For the particular case of DyCo x a few studies exist that indicate the existence of intrinsic nocollinear magnetic ground states for both single crystal and amorphous films [48,62,63]. For instance, for amorphous DyCo 3.4 it is observed that the Dy moments exhibit a sperimagnetic arrangement, whereas the Co sublattice is ferromagnetically ordered [63].…”

Plasma-induced magnetic patterning of FePd thin films without and with exchange bias

“…These kinks are of magnitude close to the noise level and therefore can be easily missed, but their reproducibility confirms their existence. The pair of top and bottom small kinks points to an additional switching field attributed to a minority soft layer in the system, [48,54] which in our case is the Pd-rich layer. These kinks have also been observed in the hysteresis loop of a SmCo film with a mixture of Sm x Co y phases being present, [48] which play similar roles to the FePd phase and the Pd-rich phase in our system.…”

Chirality of Bloch domain walls in exchange biased CoO/Co bilayer seen by waveguide-enhanced neutron spin-flip scattering

“…One of the widely used methods in studying of EB is Polarized Neutron Reflectometry (PNR) [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. In this method reflectivities R µν are measured as a function of momentum transfer Q = 4π sin θ/λ.…”