Microstructural-defect-induced Dzyaloshinskii-Moriya interaction

Abstract

The antisymmetric Dzyaloshinskii-Moriya interaction (DMI) plays a decisive role for the stabilization and control of chirality of skyrmion textures in various magnetic systems exhibiting a noncentrosymmetric crystal structure. A less studied aspect of the DMI is that this interaction is believed to be operative in the vicinity of lattice imperfections in crystalline magnetic materials, due to the local structural inversion symmetry breaking. If this scenario leads to an effect of sizable magnitude, it implies that the DMI introduces chirality into a very large class of magnetic materialsdefect-rich systems such as polycrystalline magnets. Here, we show experimentally that the microstructural-defect-induced DMI gives rise to a polarization-dependent asymmetric term in the small-angle neutron scattering (SANS) cross section of polycrystalline ferromagnets with a centrosymmetric crystal structure. The results are supported by theoretical predictions using the continuum theory of micromagnetics.This effect, conjectured already by Arrott in 1963, is demonstrated for nanocrystalline terbium and holmium (with a large grain-boundary density), and for mechanicallydeformed microcrystalline cobalt (with a large dislocation density). Analysis of the scattering asymmetry allows one to determine the defect-induced DMI constant, D = 0.45 ± 0.07 mJ/m 2 for Tb at 100 K. Our study proves the generic relevance of the DMI for the magnetic microstructure of defect-rich ferromagnets with vanishing intrinsic DMI. Polarized SANS is decisive for disclosing the signature of the defectinduced DMI, which is related to the unique dependence of the polarized SANS cross section on the chiral interactions. The findings open up the way to study defectinduced skyrmionic magnetization textures in disordered materials.

Embracing Defects and Disorder in Magnetic Nanoparticles

“…However, for magnetic materials changing our negative perception about defects has had a much slower pace than other fields. Recently, the generic relevance of the defect‐induced Dzyaloshinskii–Moriya interaction for the spin microstructure of defect‐rich ferromagnets was verified, [ 20 ] suggesting a potential for creation of local chiral spin textures, that is, skyrmions, [ 21 ] in all kinds of disordered magnetic materials. Magnetic materials offer wide‐spread novel technological potential, [ 22 ] with magnetic nanoparticles, [ 23 ] especially iron oxide nanoparticles, being indispensable candidates for varieties of biomedical applications, [ 24 ] including magnetic hyperthermia [ 25 ] and magnetic particle and resonance imaging (MPI, [ 26 ] MRI [ 27 ] ).…”

Strain-enhanced Dzyaloshinskii–Moriya interaction at Co/Pt interfaces

“…Tailoring magnetic topography of these structures requires both a deep understanding and a precise control of the DMI. A large number of studies have been carried out to understand the physical mechanisms underlying the interaction 14 – 16 . It is generally reported that electronic configuration of materials constituting the interface, designates the DMI 17 – 20 .…”

“…(2) changing stacking order or material, which can naturally vanish the DMI for the FM layer sandwiched by the same HM layers due to the inversion symmetry, to enhance total DMI in the stack 14 , 15 , 28 (3) designing electronic band structure and charge carrier density by varying the chemical composition of both magnetic and non-magnetic layers 29 , 30 . Other internal or external effects inducing the DMI are also investigated in the literature 16 , 31 , 32 . In addition to the methods mentioned above, an unsophisticated phenomenon occuring at interfaces can lead to enhanced DMI: crystal lattice strain.…”

Overcoming the Limits of the Interfacial Dzyaloshinskii–Moriya Interaction by Antiferromagnetic Order in Multiferroic Heterostructures

“…[ 46 ] Recently, oxygen octahedral tilting was also considered as an origin of DMI, which was calculated about 0.21 meV (≈2.2 × 10 −4 J m −2 ) for SRO on (001) STO. [ 13 ] Moreover, microstructural‐defect (vacancies) [ 14,47 ] was demonstrated as the new origin of bulk DMI. As well known, SrRuO 3 exhibited RuO 6 ‐oxygen octahedral rotation or tilt, and microstructural‐defect (oxygen and ruthenium vacancies).…”

“…[ 11 ] The interfacial DMI decreases rapidly with the increasing ferromagnet (FM) thickness, which determines that topological states are only hosted in ultrathin systems. [ 12 ] Moreover, oxygen octahedral rotation/tilting [ 13 ] and microstructural defects [ 14 ] are demonstrated as additional origins of the DMI. Our previous work [ 15 ] found the emergence of THE in SRO single layer with a thickness of 7–15 unit cells through the modulation of RuO 6 oxygen octahedra via oxygen engineering.…”