On-line SPICE-SPIN+X Seminars

On-line Seminar: 24 June 2020 - 15:00 (CET)

Chiral spintronics: non collinear spin textures with application to Racetrack Memory

Stuart Parkin, Max Planck Institute of Microstructure Physics and
Martin Luther University Halle-Wittenberg, Halle

Magnetic non-collinear spin textures that have chiral structures are of great current interest.  Coupled chiral domain walls in synthetic antiferromagnetic (SAF) racetracks and compensated ferrimagnets can be moved with current at very high speeds via a novel giant exchange torque^1,2. When the antiferromagnetic coupling between two domain walls in a SAF racetrack is weakened unusual magnetization dynamics takes place due to chiral domain wall drag³. The same type of Dzyaloshinskii-Moriya (DMI) vector exchange interactions that stabilize chiral Néel domain walls in magnetic multilayers results in the formation of topological spin textures in bulk compounds. We recently discovered magnetic antiskyrmions in a tetragonal inverse Heusler compound Mn_1.4Pt_0.9Pd_0.1Sn using Lorentz transmission electron microscopy (LTEM) ⁴. The size of the anti-skyrmion can be tuned by varying the thickness of the host material allowing for sizes varying from nanometer to microns in the same material⁵.  This is due to long range magneto-dipole interactions that are important in this compound that has a complex DMI interaction with a symmetry that follows the D_2d symmetry of its crystalline structure. The same symmetry ensures that anti-skyrmions are robust to temperature and magnetic field⁶. The magnetic dipole-dipole interactions also allow for the formation of metastable “elliptical skyrmions” in this same material⁷.  These have Bloch-like boundaries that we can directly observe using LTEM. Finally, we discuss our recent discovery of novel Néel like skyrmions in a metallic compound that exist almost to room temperature and that are also tunable in size⁸.  Chiral spin textures in ferro-, ferri- and anti-ferrimagnetic materials and thin film heterostructures are of fundamental interest with potential for spintronic applications.

PDF file of the talk available here

 

References

1  Yang, S.-H., Ryu, K.-S. & Parkin, S. S. P. Domain-wall velocities of up to 750 ms⁻¹ driven by exchange-coupling torque in synthetic antiferromagnets. Nat. Nano. 10, 221-226, (2015).
2  Bläsing, R. et al. Exchange coupling torque in ferrimagnetic Co/Gd bilayer maximized near angular momentum compensation temperature. Nat. Commun. 9, 4984, (2018).
3  Yang, S.-H., Garg, C. & Parkin, S. Chiral Exchange Drag and Chirality Oscillations in Synthetic Antiferromagnets Nat. Phys. 15, 543–548, (2019).
4  Nayak, A. K. et al. Magnetic antiskyrmions above room temperature in tetragonal Heusler materials. Nature 548, 561-566, (2017).
5  Ma, T. et al. Tunable Magnetic Antiskyrmion Size and Helical Period from Nanometers to Micrometers in a D_2d Heusler Compound. Adv. Mater., 2002043, (2020).
6  Saha, R. et al. Intrinsic stability of magnetic anti-skyrmions in the tetragonal inverse Heusler compound Mn_1.4Pt_0.9Pd_0.1Sn Nat. Commun. 10, 5305, (2019).
7  Jena, J. et al. Elliptical Bloch skyrmion chiral twins in an antiskyrmion system. Nat. Commun. 11, 1115, (2020).
8  Srivastava, A. K. et al. Observation of Robust Néel Skyrmions in Metallic PtMnGa. Adv. Mater. 32, 1904327, (2020).