Detection of antiskyrmions by topological Hall effect in Heusler compounds

Abstract

Heusler compounds having D2d crystal symmetry gained much attention recently due to the stabilization of a vortex-like spin texture called antiskyrmions in thin lamellae of Mn1.4Pt0.9Pd0.1Sn as reported in the work of Nayak et al. [Nature 548, 561 (2017)]. Here we show that bulk Mn1.4Pt0.9Pd0.1Sn undergoes a spin-reorientation transition from a collinear ferromagnetic to a non-collinear configuration of Mn moments below 135 K, which is accompanied by the emergence of a topological Hall effect. We tune the topological Hall effect in Pd and Rh substituted Mn1.4PtSn Heusler compounds by changing the intrinsic magnetic properties and spin textures. A unique feature of the present system is the observation of a zerofield topological Hall resistivity with a sign change which indicates the robust formation of antiskyrmions. I. INTRODUCTIONTopological magnetic textures show promise in many areas of technology, such as racetrack memory [1,2] and neuromorphic computing [3,4], due to the unique transport properties that allow for efficient manipulation [5,6] and detection [7,8] of the magnetic textures. This is a consequence of the real space Berry curvature of the topological texture that can be tuned by the electronic structure [9,10]. One such topological texture is the skyrmion [11,12] which is found in chiral magnets [13] with a unit integer topological charge.Recently antiskyrmions (aSKs) [14], the anti-particles of the skyrmions, were stabilized in thin lamellae of the tetragonal inverse Heusler compound Mn1.4Pt0.9Pd0.1Sn for a broader field range and even above room temperature [15]. In this compound (D2d symmetry class), the Dzyaloshinskii-Moriya interaction (DMI) is anisotropic where the DM vectors along the x and y directions in the basal plane are of opposite sign and hence cause the stability of the aSKs [16]. The in-plane winding of the spin texture for an aSK is anisotropic with an opposite topological charge as compared to that of the azimuthally symmetric Bloch and Néel skyrmion of the same charge [17]. The topological winding induces a real space Berry curvature that strongly influences all transport properties [18]. The topological Hall effect (THE) is one such electrical transport property that has been intrinsically linked to the skyrmions [8]. The THE results in a further component of the total Hall signal, in addition to the normal Hall and the magnetization-scaled anomalous Hall components [19]. It arises due to the emergent magnetic field which is a result of the finite Berry phase contributions from either II. EXPERIMENT Polycrystalline ingots of Mn1.4Pt1-xPdxSn (x = 0, 0.1 … 0.3) and Mn1.4Pt1-yRhySn (y = 0.1, 0.2 … 0.8) with the stoichiometric amounts of constituent elements were prepared by arcmelting in the presence of Ar atmosphere. The synthesized ingots were sealed in an evacuated quartz tube and annealed at 873 K (Pd-substituted samples) and 1073 K (parent compound Mn1.4PtSn and Rh-substituted samples) for 7 days followed by quenching into an ice-water mixture. The phase purity and the cryst...

Spin dynamics in bulk MnNiGa and Mn1.4Pt0.9Pd0.1Sn investigated by muon spin relaxation

“…Below T C in 50 µm-thick polycrystalline samples of MnNiGa, from 0.2 T < µ 0 H < 1 T, a topological Hall signal is observed, consistent with the region in which the biskyrmion state is reported in sub-µm thick lamellae [6]. In contrast, in Mn 1.4 Pt 0.9 Pd 0.1 Sn a topological Hall signal is only reported below the spin-reorientation transition for T < 150 K [8] in bulk samples. This suggest that some sort of topologically non-trivial state exists in bulk samples of both materials, and not only in thin films or lamellae.…”

“…Biskyrmions have been reported in the layered manganite La 2−2x Sr 1+2x Mn 2 O 7 [3] and in certain compositions of hexagonal MnNiGa [5,6], while antiskyrmions have so far been reported in Mn 1.4 Pt 0.9 Pd 0.1 Sn [4] and related centrosymmetric Heusler systems [7,8]. Indirect evidence for the presence of a topologically nontrivial state has been reported for these materials, and other Heusler materials related to the antiskyrmion hosts [9][10][11][12], however direct evidence for both the biskyrmion and antiskyrmion states has thus far relied on Lorentz Transmission Electron Microscopy (LTEM).…”

Skyrmion-Antiskyrmion Racetrack Memory in Rank-One DMI Materials

“…[21], information would be encoded by two distinguishable magnetic particles, e.g., a skyrmion represents the bit "1", whereas an antiskyrmion represents the "0". The distinction between the two is possible, for example, by measuring the sign of the topological Hall effect (THE) [29], which depends on the sign of the topological charge Q, which is opposite for skyrmions and antiskyrmions, or the strength of the chiral Hall effect (CHE) [30] or the noncollinear Hall effect (NHE) [31], which both vary in size depending on the type of particle. We show that skyrmions and antiskyrmions, although they carry the notion of antiparticles, can indeed coexist and even repel each other if the proper geometry of the racetrack is chosen.…”

Large topological Hall effect in an easy-cone ferromagnet (Cr0.9B0.1)Te

“…The third category covers magnetization from the hard axis, including Cr5Te8 [19] , Fe3GeTe2 [20] , and (Cr0.9B0.1)Te. Many Mn-based Heusler compounds [21][22][23][24][25]35] have combined materials from all three categories. The topological Hall effects for the second and third categories are larger, with a large magnetic field, depending on the exchange coupling strength or magnetocrystalline anisotropy.…”