X-ray ferromagnetic resonance

X-ray ferromagnetic resonance (X-FMR) combines two different techniques, x-ray magnetic circular dichroism (XMCD) and ferromagnetic resonance (FMR), for investigating magnetization dynamics.

• XMCD: The spin and orbital magnetic moment can separately be quantified by measuring the x-ray absorption at specific absorption edges. Since different elements exhibit energy separated absorption edges in the soft x-ray regime, this technique offers element selective measurements of the magnetization.
• FMR: The magnetic field of microwaves will induce oscillations of the spins in magnetic materials. At certain material specific frequencies, resonances are observed, that exhibit large amplitude oscillations. The frequency dependence of the resonance provides information about effective magnetization, damping, and spin transport.

The combination of XMCD and FMR provides the means to investigate the phase and amplitude of element selective magnetization in complex materials or structures.

These studies are performed at synchrotrons (such as Bessy in Berlin or ALS in Berkley), since they can provide intense circularly polarized soft x-rays with variable energies. The x-ray pulses are synchronized with the microwaves such that the magnetization of each element can be studied at any set phase of the microwave excitation. This is highlighted in the top figure where phase between the top and bottom magnetic layers show an π/2 phase shift due to an antiferromagnetic exchange interaction between the layers. As illustrated by this example, the method provides information about static and dynamic exchange interactions between magnetic elements.

People:

• Somnath Jana (postdoc)
• Yevgen Pogoryelov (Researcher)
• Olof Karis(Professor)
• Ronny Knut(Researcher)
• Rameez Saeed Malik (PhD student)
• Dario Arena (visiting professor)

Papers:

Detection of microwave phase variation in nanometre-scale magnetic heterostructures,
Nature Communications 4, 2025 (2013)

Exploring the accessible frequency range of phase-resolved ferromagnetic resonance detected with x-rays,
J. Applied Physics 113, 033904 (2013)