Speaker
Description
We present the status and capabilities of the pulsed magnetic field setup that is currently being comissioned at the Cristallina-Quantum experimental station of the Aramis hard X-ray beamline branch at SwissFEL. The setup is based on a split-pair coil magnet, providing a vertical magnetic field with wide horizontal scattering angle access and compatible with cryogenic sample environments. The ultimate design goals are reaching magnetic fields of up to 40 T and low temperatures down to 1 K. The magnetic field pulses are synchronized to the femtosecond X-ray pulses from SwissFEL, enabling X-ray diffraction under simultaneous high magnetic field and low temperature conditions. The experimental scope is focused on high-field investigations of quantum materials, such as resolving the structural evolution of ordered state through field-driven transitions.
As a demonstration of this capability, we present the results from a study of the multiferroic GdMn$_2$O$_5$, where electric polarization and magnetic order are strongly coupled [1]. The compound exhibits a magnetic field-induced electric polarization with a component along the crystallographic a-axis that persists even after field removal, suggesting a path-dependent ground state [2]. The microscopic mechanism behind this persistent polarization remains unclear and resolving it requires a direct structural probe to follow the lattice response in the presence of high magnetic fields. Using X-ray diffraction under pulsed magnetic fields, we directly track the structural response of the lattice across this field-driven transition. Our measurements are guided by density functional theory simulations covering scenarios ranging from simple atomic displacements of the magnetic Gd ions to lattice relaxation driven by changes of the magnetic order. These models predict intensity variations of specific lattice Bragg peaks, providing a direct experimental benchmark for the structural origin of the magnetic field-induced electric polarization.
[1] G. Yahia et al. Recognition of exchange striction as the origin of magnetoelectric coupling in multiferroics. Phys. Rev. B 95, 184112 (2017).
[2] V. Balédent et al. Electronic ground-state hysteresis under magnetic field in GdMn${_2}$O${_5}$. Phys. Rev. B 108, 104419 (2023).