Macroscopic manifestation of domain-wall magnetism and magnetoelectric effect in a Néel-type skyrmion host

Abstract

We report a magnetic state in GaV 4 Se 8 which emerges exclusively in samples with mesoscale polar domains and not in polar monodomain crystals. It is manifested by a sharp anomaly in the magnetic susceptibility and the magnetic torque, distinct from other anomalies observed also in polar mono-domain samples upon transitions between the cycloidal, the Néel-type skyrmion lattice and the ferromagnetic states. We ascribe this additional transition to the transformation of distinct magnetic textures, confined to polar domain walls (DW), to the ferromagnetic (FM) state. The emergence of these DW-confined magnetic states is likely driven by the mismatch of different spin spirals, hosted by the adjacent domains. A clear anomaly in the magneto-current indicates that the DWconfined magnetic states also have strong contributions to the magnetoelectric response. We expect polar DWs to commonly host such confined magnetic edge states and, thus, offer a fertile ground to explore novel forms of magnetism.

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8Zuo1, Kitchaev2, Schueller3 et al. 2021Phys. Rev. Materials5010View full textAdd to dashboardCite

“…We identify characteristic positive-entropy precursor effects in the cycloid phase near the cycloid-to-skyrmion transition, which can be used to identify the phase boundary between these two states. Furthermore, we identify an unusual high entropy region at the low temperature, high-field phase boundary of the cycloidal state in GaV 4 Se 8 , which may be a signature of recently proposed magnetic phases confined to polar domain walls [32]. More generally, our results demonstrate that magnetoentropic mapping informed by computational models of entropic susceptibility can provide a rapid, unambiguous measurement of cycloid/skyrmion phase boundaries in model uniaxial systems and thereby facilitate the rapid characterization of similar skyrmion phase diagrams.…”

“…This region does coincide with previously undetermined regions of the GaV 4 Se 8 phase diagram [10], which were proposed to arise due to distortions of cycloidal structure within limited structural domains. A more recent analysis of GaV 4 Se 8 has suggested that new, distinct magnetic phases may form at these fields and temperatures, confined to structural domain walls from the F43m → R3m structural transition [32].…”

“…GaMo 4 S 8 [18,29,30], and GaMo 4 Se 8 [31]. The magnetic phase boundaries of these materials have been mapped out by conventional techniques, including SANS, field-dependent magnetization, probe microscopy, and AC susceptibility [10,11,[31][32][33]. Furthermore, lacunar spinels are ferroelectric [10,11,34] and susceptible to structural phase transitions [31], meaning that skyrmion stability can be probed using electric fields and mechanical strain [32].…”

“…The magnetic phase boundaries of these materials have been mapped out by conventional techniques, including SANS, field-dependent magnetization, probe microscopy, and AC susceptibility [10,11,[31][32][33]. Furthermore, lacunar spinels are ferroelectric [10,11,34] and susceptible to structural phase transitions [31], meaning that skyrmion stability can be probed using electric fields and mechanical strain [32]. Finally, while the electronic structure of these materials is highly correlated and requires advanced computational methods to resolve [28,35], their microscopic magnetic behavior is well-captured using semi-classical spin models [18,30,36].…”

Field‐Free Manipulation of Skyrmion Creation and Annihilation by Tunable Strain Engineering

“…By increasing H, the stripe domains first fractured into small pieces and then transformed into skyrmions, owing to a delicate interplay of the interfacial DMI, magnetic anisotropy, dipolar interaction, and Zeeman interaction. [29][30][31] The critical magnetic field (H cri ), in which the stripe domains began to transform into skyrmions, was determined to be about 700 Oe for the current sample. When a compressive strain ε of −2.7% was applied, we observed a striking change in the field-dependent domain evolution during which the stripe domains directly transformed into out-of-plane ferromagnetic domains without the formation of any skyrmions (see the first row of Figure 2b).…”