Unexpected observation of splitting of skyrmion phase in Zn doped Cu2OSeO3

Abstract

Polycrystalline (Cu1−xZnx)2OSeO3 (0 ≤ x ≤ 0.2) samples were synthesized using solid-state reaction and characterized by X-ray diffraction (XRD). The effect of Zn doping upon saturation magnetization (MS) indicates that the Zn favors to occupying Cu(II) square pyramidal crystallographic site. The AC susceptibility (χ′ac) was measured at various temperatures (χ′ac–T) and magnetic field strengths (χ′ac–H). The Zn doping concentration is found to affect greatly the M-T and χ′ac-T. The skyrmion phase has been inferred from the χ′ac-H data, and then indicated within the H-T phase diagrams for various Zn doping concentrations. The striking and unexpected observation is that the skyrmion phase region becomes split upon Zn doping concentration. Interestingly, second conical boundary accompanied by second skyrmion phase was also observed from dχ′ac/dH vs. H curves. Atomic site disorder created by the chemical doping modulates the delicate magnetic interactions via change in the Dzyaloshinskii-Moriya (DM) vector of distorted Cu(II) square pyramidal, thereby splitting of skyrmion phase might occur. These findings illustrate the potential of using chemical and atomic modification for tuning the temperature and field dependence of skyrmion phase of Cu2OSeO3.

Chiral Magnetism and High-Temperature Skyrmions in B20-Ordered Co-Si

“…5(a). χðHÞ exhibits an anomaly between the fields H A1 ¼ 0.14 and H A2 ¼ 0.32 kOe, similar to those observed for skyrmion spin structures in other systems [35][36][37][38][39][40][41][42][43][44][45]. Note that MðHÞ data in Fig.…”

“…The chiral spin structure of B20 magnets is well known to support spin spirals (helices) [4] and skyrmions [1-3, 5,7]. Such noncollinear spin structures can be investigated by analyzing the field dependences of MðHÞ and χ ¼ dMðHÞ=dH, where they give rise to characteristic features or anomalies just below T c in single crystals, thin films and polycrystalline samples, corresponding to skyrmion spin structures [3,[35][36][37][38][39][40][41][42][43][44][45]. The room-temperature field dependences of M and χ for x ¼ 0.043 sample are shown in Fig.…”

Origin of skyrmion lattice phase splitting in Zn-substitutedCu2OSeO3

“…Magnetic interactions between spins are mediated through oxygen atoms via ferromagnetic and antiferromagnetic superexchange interactions [23,24]. As reported by Wu et al [17], the magnetic moment of Cu 2 OSeO 3 monotonically decreases with increasing Zn-substitution levels, which they interpret in terms of the site-specific substitution of Cu 2+ cation at the Cu site with nonmagnetic Zn 2+ . This is accompanied by a splitting of the SkL phase observed in pristine Cu 2 OSeO 3 into two distinct pockets.…”

“…An alternative route to expand the number of skyrmionic materials is to utilize a chemical doping/substitution strategy in known skyrmion-hosting systems. This approach has recently been adopted in Cu 2 OSeO 3 , where Zn substitution led to observation of splitting of the skyrmion lattice (SkL) phase into two distinct pockets [17], and Ni substitution led to an expansion of the SkL phase [18].…”

Multiple low-temperature skyrmionic states in a bulk chiral magnet

“…Their stability is attributed to the competition between the ferromagnetic exchange, the Dzyaloshinskii-Moriya (DM) and Zeeman interactions in combination with additional small terms, 15 such as thermal fluctuations, 8,16 dipolar interactions and the softening of the magnetization modulus. 17,18 As the free energy imbalance between the skyrmion lattice phase and its main competitor, the conical state, is small, the boundaries of the A-phase can be changed substantially by applying pressure, 19 electric fields, 13,[20][21][22] chemical doping, 23 or uniaxial strains. 24,25 On the other hand, theoretical models that are based on the Dzyaloshinskii approach 26,27 and include magnetic stiffness or anisotropy, predict SkLs to occur in bulk cubic helimagnets over a wide range of magnetic fields and temperatures below T C .…”