X-Ray Detected Magnetic Resonance at Sub-THz Frequencies Using a High Power Gyrotron Source

Abstract

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy which makes use of X-ray Magnetic Circular Dichroism (XMCD) to probe the resonant precession of local magnetization components in a strong microwave pump field. In Sections 1 and 2, we briefly review the conceptual bases of XDMR and the potential interest of increasing the pumping frequency up to the THz frequency range. In Sections 3-5, we discuss the feasibility of such challenging experiments. Starting from a comparison of experiments carried out either in the transverse (TRD) or longitudinal (LOD) detection geometries, we show that XDMR measurements at sub-THz frequencies require a substantial increase in pumping power: this is where a gyrotron source looks most appropriate. It is the aim of this paper to discuss how to conduct such experiments, emphasis being laid on feasibility tests recently carried out at the ESRF using a refurbished version of Gyrotron FU-II built at the FIR-FU. In this context, we propose a new detection scheme of sub-THz XDMR spectra based on the concept of frequency-mixing in LOD geometry.

Exploring the accessible frequency range of phase-resolved ferromagnetic resonance detected with x-rays

“…Furthermore, experimental schemes to transferring the XFMR technique to fourth generation synchrotrons, where photon bunch lengths in the sub-ps regime can be achieved, have recently been proposed. 27 In conclusion, experimental measurements of the upper accessible frequency for transmission mode XFMR exceed the inverse bunch length. The observed upper accessible frequency is supported by a numerical model, which accounts for the sampled amplitude dependence on the pump frequency as well as the time structure of the probe, i.e., the bunch length and timing jitter.…”

The Gyrotrons as Promising Radiation Sources for THz Sensing and Imaging

“…The XDMR spectroscopy is a new and unique element-and edge-selective technique [75] which allows to resolve and study the precession dynamics of spin and local orbital magnetization components. In this Pump&Probe technique (see Figure 6), the X-ray magnetic circular dichroism (XMCD) is used to probe the resonant precession of the magnetization produced by the irradiation with a strong microwave pump wave applied perpendicularly to the static magnetic field.…”

X-Ray Detected Magnetic Resonance: A Unique Probe of the Precession Dynamics of Orbital Magnetization Components

“…So-far, we discussed XDMR spectra recorded only on ferrimagnetic films or crystals. In collaboration with the research center for the development of the far infrared region (University of Fukui, Japan), we are presently testing at the ESRF the feasibility of high-field XDMR experiments at sub-THz pumping frequencies [ 74 , 75 ]. Our ultimate goal is to evaluate whether high-field X-ray detected Electron Paramagnetic Resonance (EPR) spectra could be successfully recorded in longitudinal detection geometry (LOD).…”

“…From a technical point of view, there is also the further handicap that the superheterodyne detection scheme discussed in Section 2.6 cannot be extended beyond F p = 20 GHz: this implies that, as yet, X-ray detected EPR spectra could be recorded at sub-THz frequencies only in the longitudinal detection geometry (LOD) which suffers from a very poor sensitivity. This point justifies the need for a powerful pumping source such as a gyrotron [ 74 , 75 ].…”