Spin transport

Spintronics based on hybrid devices comprising magnetic and semiconducting (nonmagnetic) materials can perform the processing, communication, and storage of information within one chip. The investigations on spin transport phenomena in ferromagnet/nonmagnet hybrid structures aim at the understanding of the underlying physical mechanisms as well as the evaluation of their relevance for spintronic device concepts.

In the field of spintronics based on two-dimensional (2D) materials, our major goal is to identify novel opto-spintronic phenomena that arise from strong proximity-induced exchange and spin-orbit coupling in van-der-Waals heterostructures (vdWHs) made from atomically thin 2D ferromagnets (2DFMs) and non-magnetic materials (2DNMs). The 2D material Fe_5-xGeTe₂ which exhibits ferromagnetic order above room temperature has been successfully grown at the PDI by molecular beam epitaxy and will be the 2DFM of choice for most studies. Various large-area grown 2DNMs, specifically graphene, transition metal dichalcogenides (such as MoS₂ and WSe₂) and hexagonal boron nitride can be integrated into the vdWHs using top-down and bottom-up approaches. For spintronic applications, current-induced magnetization switching, charge-to-spin interconversion phenomena as well as electrical and optical spin-dependent gating are the focus of our research. 

In order to boost the progress in the field of oxide spintronics, we focus our activities on the inverse spinel oxide NiCo₂O₄ (NCO). In addition to the ferrimagnetic order above room temperature, this material stands out by the tunability of several material properties in wide ranges. In fact, tailoring the characteristics of individual films allows to design complete spintronic multilayer devices consisting only of NCO. With the realization and optimization of the film synthesis by molecular beam epitaxy at the PDI, a major improvement regarding the independent tailoring of specific NCO properties is expected - leading to an extended degree of freedom in the design of building blocks for oxide spintronics.

Author: H. Lv, X. C. Huang, K. H. L. Zhang, O. Bierwagen, M. Ramsteiner
Title: Underlying Mechanisms and Tunability of the Anomalous Hall Effect in NiCo2O4 Films with Robust Perpendicular Magnetic Anisotropy
Source: Advanced Science 2023
DOI: 10.1002/advs.202302956

Author: H. Lv, A. Da Silva, A. I. Figueroa, C. Guillemard, I. Fernández Aguirre, L. Camosi, L. Aballe, M. Valvidares, S.O. Valenzuela, J. Schubert, M. Schmidbauer, J. Herfort, M. Hanke, A. Trampert, R. Engel-Herbert, M. Ramsteiner, J. M. J. Lopes
Title: Large-area synthesis of ferromagnetic Fe5-xGeTe2/graphene van der Waals heterostructures with Curie temperature above room temperature
Source: Small, 1, 2302387 (2023)
DOI: 10.1002/smll.202302387

Author: D. Czubak , S. Gaucher , L. Oppermann , J. Herfort , K. Zollner , J. Fabian , H. T. Grahn , M. Ramsteiner
Title: Electronic and magnetic properties of alpha-FeGe2 films embedded in vertical spin valve devices
Source: Phys. Rev. Mater. , 4 , 104415 ( 2020 )
DOI: 10.1103/PhysRevMaterials.4.104415