Reciprocal space tomography of 3D skyrmion lattice order in a chiral magnet

Abstract

It is commonly assumed that surfaces modify the properties of stable materials within the top few atomic layers of a bulk specimen only. Exploiting the polarization dependence of resonant elastic X-ray scattering to go beyond conventional diffraction and imaging techniques, we have determined the depth dependence of the full 3D spin structure of skyrmions-that is, topologically nontrivial whirls of the magnetization-below the surface of a bulk sample of CuOSeO We found that the skyrmions change exponentially from pure Néel- to pure Bloch-twisting over a distance of several hundred nanometers between the surface and the bulk, respectively. Though qualitatively consistent with theory, the strength of the Néel-twisting at the surface and the length scale of the variation observed experimentally exceed material-specific modeling substantially. In view of the exceptionally complete quantitative theoretical account of the magnetic rigidities and associated static and dynamic properties of skyrmions in CuOSeO and related materials, we conclude that subtle changes of the materials properties must exist at distances up to several hundred atomic layers into the bulk, which originate in the presence of the surface. This has far-reaching implications for the creation of skyrmions in surface-dominated systems and identifies, more generally, surface-induced gradual variations deep within a bulk material and their impact on tailored functionalities as an unchartered scientific territory.

Seeing is believing: visualization of antiferromagnetic domains

“…88 Probing AFM domains with synchrotron X-rays Since the first measurement of X-ray magnetic scattering at the beginning of the 1980s, 103,104 probing AFM states and their domain structure with sub-micron resolution has become possible thanks to the multifold increase in spectral brightness at synchrotron sources over the last decades. One can classify the type of studies in three main categories: (1) scattering experiments with a micro-or nano-focused X-ray beam, in the hard or soft X-ray regime, where it is possible to simultaneously spatially resolve the AFM wave-vector and magnetization density, including chirality of the different domains, and in some cases their depth dependence, 105 (2) scanning X-ray microscopy and X-ray photo emission electron microscopy (PEEM) both using the absorption contrast produced by magnetic linear dichroism to probe the moment direction along the polarization direction of the incident light, and (3) coherent X-ray imaging in Bragg condition, to image certain types of AFM domains. 106 In the hard X-ray regime, and away from atomic resonances, coupling of the photon field to spin and orbital momentum of the electron is intrinsically weak (of the order hν/(mc 2 ), compared to Thomson scattering.…”

“…Additionally, in the soft regime, it is possible to exploit the large change in absorption at energies close to certain atomic resonance to probe the change in magnetization as of function of depth, virtually impossible to access with other techniques. This was employed successfully recently to probe the magnetization reconstruction of skyrmion lattices close to the surface, 105 and could possibly be exploited to access domain information in buried interfaces. Magnetic soft X-ray scattering is unfortunately limited since the Bragg condition can only be satisfied for small momentum transfer (i.e.…”

Organic enantiomeric high- T c ferroelectrics

“…Homochiral systems not only have been widely involved in chemical processes such as catalysis, chiral separation, enantioselective sensors, and molecular recognition, but also have played a crucial role in specific physical properties due to the compatibility between the corresponding electronic, optical, magnetic, and structural properties (7)(8)(9)(10)(11)(12)(13). The intriguing physical phenomena including chiral magnetic effect, chiral superconductivity, and chiral photonics, offer them a wide range of applications in optoelectronics, information storage, polarization optics, spintronic devices, liquid crystal displays, chiroptical switches, and nanomotors (14)(15)(16)(17)(18)(19)(20)(21). As an important subject of ferroelectrics in classical physics, it is of great potential to incorporate the homochirality to ferroelectricity to broaden much more fascinating applications.…”

Ferromagnetic Resonance with Magnetic Phase Selectivity by Means of Resonant Elastic X-Ray Scattering on a Chiral Magnet

“…The intensity of a crystalline Bragg peak or magnetic satellites may be studied, permitting to clearly identify the hosting magnetic state of a given excitation via the scattering pattern in reciprocal space. As a point of reference, we demonstrate the potential of REXS-FMR using the insulating cubic chiral magnet Cu 2 OSeO 3 , which was studied previously both by means of REXS [26][27][28][29][30][31] and standard microwave spectroscopy [11,12,[32][33][34][35][36].…”

“…At intermediate magnetic field just below T c , a pocket of skyrmion lattice state is observed. The trigonal order of the spin whirls in the plane perpendicular to the field translates to the characteristic sixfold pattern of magnetic satellites in both small-angle neutron scattering [41][42][43][44][45] and REXS [26][27][28][29][30][31], as shown in Fig. 1(e).…”