In‐Depth NMR Investigation of the Magnetic Hardening in Co Thin Films Induced by the Interface with Molecular Layers

Abstract

The hybridization of the surface orbitals of thin ferromagnetic layers with molecular orbitals represents a soft but efficient technology that is able to induce in ferromagnetic component radical modifications of the key magnetic parameters, such as magnetization, magnetic anisotropy, and others. These effects are investigated in 7 nm thick polycrystalline Co films interfaced with C60 and Gaq3 molecular layers by combining 59Co Ferromagnetic nuclear resonance spectroscopy (FNR) and magneto‐optic kerr effect (MOKE) techniques. It is demonstrated that the surface hybridization produces a significant magnetic hardening with respect to a reference Co/Al system and that the molecule‐induced effects modify the magnetic properties of entire Co layer, propagating for several nm from the interface. The FNR spectroscopy also reveals a reconstruction of the magnetic environment at the cobalt surface, whose observation in polycrystalline films is especially intriguing. The results shed new and unexpected light on the interfacial physics in such systems, whose understanding necessitates further experimental and theoretical research.

Enhancement of Magnetic Stability in Antiferromagnetic CoO Films by Adsorption of Organic Molecules

“…We move to the magnetic characterization of samples with the aim of investigating the effects of the organic molecules. Longitudinal MOKE measurements performed at 295 K, i.e., above the nominal bulk Néel temperature T N ∼ 291 K of the CoO, with the applied magnetic field at various azimuthal angles ϕ with respect to the sample orientation in the configuration shown in Figure b, evidence the presence of an in-plane uniaxial anisotropy for Co layer as shown in Figure a and evidenced in previous studies for the same growth conditions . The hysteresis loops shown in Figure c of the Co layers do not present any EB effect, as expected at temperatures above the T N .…”

“…The ability of organic molecules to modify magnetic states has been tested both theoretically , and experimentally , on FM layers thanks to the hybridization between the d orbitals of the FM and the π orbitals of the molecules. Such orbital redistribution impacts both the exchange interaction and the magnetic anisotropy energy producing an increase in the Curie temperature as well as of the magnetic coercivity fields .…”

“…The spinterface formation affects the spin properties of both interface components. For example, it is responsible for the generation of spin polarization in the molecules , and for the change of the magnetic behavior of the ferromagnetic (FM) layer. , An emblematic example is provided by the adsorption of buckminster fullerene molecule (C 60 ) onto a cobalt (Co) layer: as a result of hybridization between metallic d z 2 and carbon p z orbitals, the Co layer acquires an out-of-plane interfacial anisotropy that is able to give rise to a spin reorientation transition from in-plane to out-of-plane magnetization. Hybridization effects have been widely investigated both theoretically and experimentally considering FM metallic layers − while the adsorption and coupling of molecules on oxide surfaces with antiferromagnetic (AF) order have not been elucidated yet. − The investigation of such effects on systems featuring complex spin configurations allows thus to enrich our fundamental knowledge of spinterfaces and also to explore the possibility of tuning with molecules some intrinsic AF properties such as ultra-fast magnetization dynamics and magnon-mediated spin transport .…”

“…For example, it is responsible for the generation of spin polarization in the molecules 4 , 5 and for the change of the magnetic behavior of the ferromagnetic (FM) layer. 6 , 7 An emblematic example is provided by the adsorption of buckminster fullerene molecule (C 60 ) onto a cobalt (Co) layer: 7 as a result of hybridization between metallic d z 2 and carbon p z orbitals, the Co layer acquires an out-of-plane interfacial anisotropy that is able to give rise to a spin reorientation transition from in-plane to out-of-plane magnetization. Hybridization effects have been widely investigated both theoretically and experimentally considering FM metallic layers 8 − 10 while the adsorption and coupling of molecules on oxide surfaces with antiferromagnetic (AF) order have not been elucidated yet.…”

The Ferromagnetic Glass State: collapse of the standard ferromagnetic domain structure

“…Our findings are then rationalised by a micromagnetic model, which establishes the conditions for the FGS and by density-functional-theory (DFT) calculations, which provide the ab initio foundation of the model. Importantly, the effect discussed here, caused by the 2D hybrid interface, expands to a few nanometres into the 3D body of the cobalt film 16 . This suggests that metal/organic hybrid systems may offer a new playground for engineering the coercivity of ferromagnets, and ultimately for the design of novel high-performing magnets.…”