Temperature dependence of magnetically dead layers in ferromagnetic thin-films

Abstract

Polarized neutron reflectometry has been used to study interface magnetism and magnetic dead layers in model amorphous CoFeB:Ta alloy thin-film multilayers with Curie temperatures tuned to be below room-temperature. This allows temperature dependent variations in the effective magnetic thickness of the film to be determined at temperatures that are a significant fraction of the Curie temperature, which cannot be achieved in the material systems used for spintronic devices. In addition to variation in the effective magnetic thickness due to compositional grading at the interface with the tantalum capping layer, the key finding is that at the interface between ferromagnetic film and GaAs(001) substrate local interfacial alloying creates an additional magnetic dead-layer. The thickness of this magnetic dead-layer is temperature dependent, which may have significant implications for elevated-temperature operation of hybrid ferromagnetic metal-semiconductor spintronic devices.

Threshold interface magnetization required to induce magnetic proximity effect

“…Experimental details can be found in the supplementary material 32 . We have found that Ta can diffuse vertically within this amorphous alloy during film deposition, and that subtle vertical diffusion of Ta within CFTB causes variation in the local M and T C 33 . This is similar to Fe (100−x) Ta x amorphous alloys, where T C can be tuned from ∼ 200 K to below 100 K by increasing x from ∼ 15 % to ∼ 30 % 34 .…”

Magnetic phase transitions due to compositional variation across amorphous thin–films

“…Previously, Ta diffusion within the CoFeTaB layer has been observed during the thin-film deposition, which causes variation of magnetization and TC through the thin-film [14]. As many spintronic devices work at elevated temperatures, understanding the Ta diffusion on the magnetic properties of CoFeTaB thin-film is important for the development of spintronic applications.…”