Engineering magnetic coupling through the interface structure and chemistry

|

The ever-growing role of Information and Communication Technology (ICT) in modern life demands memory devices offering fast access, increased space, and reduced energy consumption. In 1988, the discovery of giant magnetoresistance has caused a revolution in storage technology, giving birth to the novel field of spintronics. At variance with simple electronics, a spintronic device uses both the electron spin and charge to transfer and store data. Spintronic devices, such as the spin valve, exploit the change in electrical resistance caused by the alignment of the magnetisation in thin layers of ferromagnetic, antiferromagnetic and non-magnetic materials.

CERIC internal research project MAG-ALCHEMI focuses on the atomic-scale engineering of magnetic metamaterials, a key factor for the technological transition. The project, led by Dr. Andrea Locatelli (Elettra Sincrotrone Trieste), resulted in a series of publications and, among them, a research paper on the chemistry-dependent magnetic properties at the oxide-metal interface on an iron (Fe)-nickel (Ni) alloy film. This potential candidate for a spin valve, a typical building block for a spintronic device, is composed of the most abundant metals on Earth, thus representing a sustainable choice. The mentioned work shows that the spontaneously-formed oxide-metal interface in Fe-Ni alloy films has the ingredients for being put to use in such magnetic stacks.

The thermal oxidation of FeNi alloy composed by islands of two crystallographic phases (visible in the microscopic image) produces a magnetic oxide layer on top of the metallic substrate. The orientation of the magnetic domains of the oxide is either parallel or antiparallel in respect to the one in the metallic layer, depending on its crystal phase

Dr. Francesca Genuzio (CERIC-ERIC) and colleagues, in collaboration with the Jerzy Haber Institute of Catalysis and Surface Chemistry, in Kraków (Poland), worked on novel principles for engineering structure and chemistry-dependent magnetic coupling at interfaces consisting of Fe, Ni and their oxides. Spectroscopic photoemission and low-energy electron microscopy (SPELEEM) technique, available at the Nanospectroscopy beamline at the Italian CERIC Partner Facility at Elettra, was employed to study the partial oxidation of Fe-Ni alloy ultrathin films forming a magnetic oxide, termed as ferrite, which is naturally stable in ambient conditions.

This study demonstrated that the stoichiometry and crystalline structure of the pristine Fe-Ni phase influences not only the oxidation kinetics and the thickness of the oxide layer, but also the magnetic coupling between the metallic alloy film and the oxide overlayer. Ultimately, the result was a cost-efficient magnetic metal/oxide hetero-junction of high crystalline quality, thus giving concrete guidelines for optimizing a FeNi-based “spin-valve” based on the appropriate choice of the alloy phase.

ORIGINAL ARTICLE:

CHEMISTRY-DEPENDENT MAGNETIC PROPERTIES AT THE FENI OXIDE–METAL INTERFACE. GENUZIO, F., MENTEŞ, T. O., FREINDL, K., SPIRIDIS, N., KORECKI, J., & LOCATELLI, A. (2020). JOURNAL OF MATERIALS CHEMISTRY C, 8(17), 5777-5785.