Show Abstract ▼

Abstract: The significance of spin transport over an interface in energy-efficient spintronic devices has stimulated interest in the spintronic society during the last few decades. Here, interfaces of permalloy / Cu 1 − x Tb x (Py/Cu-Tb) were investigated in depth. As the Cu-Tb thickness increases, we found that the saturation magnetization of the bilayers falls and then plateaus. Element-specific x-ray magnetic circular dichroism studies suggest that the Tb moment aligns opposite to the Fe and Ni moments, forming a self-assembled antiferromagnetic interface. As a result, the Cu-Tb adjacent layer to Py and the interface have a significant impact on spin transport. Relevant parameters, such as spin mixing conductance, spin diffusion length, and damping, can be tuned by inserting a thin Cu layer between Py and Tb or varying the compositions of Cu-Tb alloys. Using rare-earth Tb, we provide an effective method for controlling the spin transport and magnetism of ferromagnet/normal-metal interfaces. This approach is expected to have a great deal of potential in spintronic applications.

Open Access

Show Abstract ▼

Abstract: A major challenge in topological magnetism lies in the three-dimensional (3D) exploration of their magnetic textures. A recent focus has been the question of how 2D skyrmion sheets vertically stack to form distinct types of 3D topological strings. Being able to manipulate the vertical coupling should therefore provide a route to the engineering of topological states. Here, we present a new type of axially bound magnetic skyrmion string state in which the strings in two distinct materials are glued together across their interface. With quasi-tomographic resonant elastic X-ray scattering, the 3D skyrmion profiles before and after their binding across the interface were unambiguously determined and compared. Their attractive binding is accompanied by repulsive twisting; i.e., the coupled skyrmions mutually affect each other via a compensating twisting. This state exists in chiral magnet–magnetic thin film heterostructures, providing a new arena for the engineering of 3D topological phases.

Open Access

Show Abstract ▼

Abstract: Single-crystal exchange biased multilayer thin-films consisting of an Fe layer on single-crystal chemically ordered L12-IrMn3 and disordered γ-IrMn3 were investigated using circularly and linearly polarised soft X-ray reflectivity to de- termine the interfacial magnetic structure between Fe and IrMn3. In ordered L12-IrMn3, we found that the Mn uncompensated moments at the interface are strongly pinned and only Fe rotational moments are observed. In disor- dered γ-IrMn3 the uncompensated moments are partially pinned, where the Mn moments are rotatable but the rotations are restricted. These findings are a crucial development in exchange bias theory to understand the force that drives the magnetic reversal process in ordered and disordered IrMn3.

Open Access

Show Abstract ▼

Abstract: As an emerging class of two-dimensional (2D) materials, van der Waals (vdW) magnets have attracted a lot of research attention since they can give access to fundamental physics and potential spintronic device applications. Among these 2D vdW magnets, CrSiTe3, as an intrinsic ferromagnetic semiconductor, exhibits great potentials in low-dimensional spintronics. Of particular interest in this 2D vdW magnet is the electronic and magnetic properties at the atomic-scale, which has yet been fully explored so far. Here, combing angle-resolved photoemission spectroscopy, bulk magnetic measurements, and synchrotron-based x-ray techniques, an unambiguous picture of the electronic and magnetic states of CrSiTe3 is presented. Hybridization of Cr-3d and Te-5p orbitals and the semiconducting behavior are confirmed by the band structure detection. Intrinsic ferromagnetism with a magnetic anisotropy constant of 1.56 × 105 erg/cm3 is attributed to the superexchange interaction of the Cr3+ ions. In addition, temperature-dependent spin and orbital moments are determined, and a fitted critical exponent of 0.169 implies that CrSiTe3 is in good agreement with the 2D Ising model. More remarkably, unquenched orbital moments are experimentally evidenced, bringing CrSiTe3 with orbital-dependent intriguing effects and great potentials toward the spintronic devices.

Show Abstract ▼

Abstract: Transition metal oxides exhibit a variety of physical properties due to their high tunability of spin, orbital, and charge degrees of freedom. This thesis studies two complex, transition metal oxide thin film/substrate systems, the NiFe2O4/Nb:SrTiO3 (NFO/STO) and the La0.3Sr0.7MnO3/Nb:SrTiO3 (LSMO/ STO). NFO is a ferrimagnetic insulator. LSMO is a ferromagnetic half metal and below a critical thickness transitions to an insulator. However, the physical properties of those complex oxides heterostructures are often directly linked to the quality of the thin oxide film and the interactions between the oxide thin film and its substrate at the interface. In this thesis the ultra thin NFO film growth via pulsed laser deposition is optimized. First those optimized, smooth and single crystalline NFO films are studied with lab measurement methods to ensure a high film quality. In a next step their stoichiometry and crystalline occupancy is studied via hard X-ray photoemission (HAXPES) and X-ray absorption spectroscopy, which were recorded at the large scale synchrotron BESSY II, PETRA III and the DIAMOND Light source. The stoichiometry and occupancy is found to match the theoretical expectations of the NFO oxide in the inverse spinel structure. The magnetic response of the NFO/STO heterostructure is researched with the element selective X-ray magnetic circular dichroism (XMCD). Due to the proximity effect the Ti signal mimics the ferrimagnetic response of the NFO thin film. The electronic properties of Au/NFO/STO and Pt/LSMO/STO devices were investigated via in-operando HAXPES measurements. In-operando HAXPES is recording HAXPES spectra during a voltage is applied to the sample. The band alignment and band bending are investigated by applying Kraut' s method to the HAXPES spectra.