For future wireless communications, the so-called mm-waves are a promising solution to cope with the ever-increasing data traffic. These waves come from a region of the electromagnetic spectrum where plenty of bandwidth is available, and their high frequencies, of tens to hundreds of GHz, allow faster data transmission rates. However, the challenge of mm-waves is that they are blocked by obstacles such as walls or trees and only allow line-of-sight propagation. This imposes a real change of paradigm, in which the mm-wave communications rely on myriads of closely scattered small antennas. Thus, the new wireless systems require affordable, low-power miniaturized devices.
FeMiT has focused on enabling the mm-wave transition for a key component of wireless communication systems: the circulator, which isolates emitting antennas from one another and allows simultaneous transmission and reception. More specifically, the overarching goal of FeMiT was to develop a new family of ferrites that can be used to fabricate miniaturized mm-wave circulators. The ferrites currently used in circulators can only operate in the first portion of the mm-wave band, using external magnetic fields, which makes the device bulky, expensive and can only work at one frequency. The key functional property of ferrites exploited in circulators is their ferromagnetic resonance (FMR), by which, at a given frequency, the propagation or absorption of electromagnetic waves through a ferrite is non-reciprocal, i.e. it depends on their direction with respect to the magnetization. Since the frequency at which the FMR occurs increases with the magnetic anisotropy of the ferrite, very high magnetic anisotropy ferrites are needed for operating at mm-waves. FeMiT has been developing a new family of ferrites based on epsilon-Fe2O3, a material with a high magnetic anisotropy, which can work in non-reciprocal wireless components at higher frequencies without the need for external magnetic fields. Moreover, we have investigated how the magnetic anisotropy of epsilon-Fe2O3 can be modified by strain, as a way to tune its FMR and the operation frequency of circulators based on this family of ferrites.
