Controlling Dzyaloshinskii-Moriya interactions in the skyrmion host candidates FePd1−xPtxMo3N

Abstract

Ferromagnets crystallizing in structures described by chiral cubic space groups, including compounds with the B20 or β-Mn structures, are known to host long-period chiral spin textures such as skyrmion lattices. These spin textures are stabilized by a competition between ferromagnetic exchange and antisymmetric Dyzaloshinskii-Moriya (DM) exchange, which is enhanced by the spin-orbit coupling associated with high-atomic-number elements. For real-world application, it is desirable to find materials that can host compact skyrmion lattices at readily accessible temperatures. Here, we report on the crystal chemistry and magnetic phase diagrams of a family of compounds with the filled β-Mn structure, FePd1−xPtxMo3N with TC ranging from 175 K to 240 K. DC and AC magnetization measurements reveal magnetic phase diagrams consistent with the formation of a skyrmion pocket just below TC . The magnitudes of ferromagnetic and DM exchanges are determined from the phase diagrams, demonstrating that the introduction of increasing amounts of Pt can be used to increase spin-orbit coupling in order to control the expected skyrmion lattice parameter between 140 nm and 65 nm while simultaneously increasing TC .

Robust metastable skyrmions with tunable size in the chiral magnet FePtMo3N

“…To conclude, we showed that FePtMo 3 N orders in a helical magnetic structure below T C of 222 K with a spiral period of ∼120 nm just below the T C and ∼210 nm at 5 K. Upon application of a magnetic field at temperatures close to T C , the helical structure of FePtMo 3 N transforms into the SkL, confirming the interpretation of recent magnetic susceptibility measurements [28]. Moreover, the SkL shows a robust metastability down to low temperatures and zero field, placing FePtMo 3 N next to the Co 8 Zn 8 Mn 4 and Co 9 Zn 9 Mn 2 compounds, whose properties were deemed unique up to date.…”

“…Having precisely determined the propagation vector in FePtMo 3 N and its temperature variation, we turn to the field response of the magnetic texture. It was shown in a previous study by magnetic measurements [28] that the A phase, which is expected to host skyrmions, occurs upon an application of a magnetic field of ∼10-20 mT in a temperature range of a few degrees Kelvin just below T C . To explore if a metastable SkL state can also exist at lower temperatures and zero field, we measured the SANS intensity with the following field protocol: (1) Cool the sample in a field of −13 mT (through the stable SkL state) down to 214.5 K, (2) sweep the field from −13 to +50 mT, and (3) sweep the field from +50 to −50 mT.…”

“…A polycrystalline sample used in the present measurements was synthesized as described in Ref. [28]. Figure 1(a) shows a SANS pattern collected at a sample temperature of 230 K, which is just above T C .…”

“…As follows from this theory [13,14,33,34], the relation reads gμ B H c2 = JSa 2 q 2 , where J is the effective exchange constant, S is the ordered spin, and a is the lattice constant. Because J can be estimated from the Curie temperature [18,28], one can calculate the predicted value of q (and the spiral period λ) from the experimental data on H c2 . Surprisingly, our measurements showed that the actual spin modulation period in FePtMo 3 N is more than a factor of 3 longer at low temperature, λ expt ∼ 210 nm, as compared to λ calc = 65 nm.…”

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8Zuo1, Kitchaev2, Schueller3 et al. 2021Phys. Rev. MaterialsSelf Cite8010View full textAdd to dashboardCite

“…This technique is complementary to conventional magnetic susceptibility (dM/dH) T measurements that can identify magnetic phase boundaries [9][10][11][12] but are unable to distinguish skyrmions from other metamagnetic phase transitions. Several proofof-concept studies have shown that magnetoentropic mapping can identify skyrmion stability regions near T c (the Curie temperature) in conventional cubic skyrmion hosts [8,[13][14][15][16]. However, the applicability of this technique to more general types of magnetic phase diagrams remains undemonstrated [17].…”