Disentangeling subsystems during 1st order magnetic phase transitions with ULMAG
Katharina Ollefs , University of Duisburg-Essen, Germany
Multi-stimuli responsive functional materials with strong interplay between their structural, magnetic, and electronic degrees of freedom appear at the forefront of research in material science [1]. In such materials, exhibiting for example a first-order phase transition, the changes caused by external impact in one subsystem of the solid (e.g. change of magnetization induced by a magnetic field), immediately gives rise to significant transformations occurring in other subsystems (e.g. expansion of the crystal lattice, change in electrical resistivity, heating of the sample, etc.) [2].
Therefore, it is vitally important to know in detail, which system triggers the phase transition, how different subsystems of the solid interplay, and how this mutual entanglement can be responsible for the resulting effect [3]. To study this mutually interrelated effects occurring during the phase transition the measurements of
magnetization M, magnetostriction λ, resistivity ρ and thermal responses ΔT and ΔS have to be performed simultaneously (or at least under strictly the same experimental conditions) [4]. To exploit element-specific characterization by X-ray absorption spectroscopy (XAS) and magnetic X-ray Magnetic Circular Dichroism (XMCD) that offers the possibility to determine separately the spin and orbital magnetic moments in an element selective manner, we constructed a novel measurement setup called “ULMAG” (that was funded by the BMBF), which allows to measure the macroscopic properties named above together with x-ray absorption spectroscopy (and diffraction) at beamline ID12 [7, 8].
To demonstrate the capability of our technique, I will present several examples of measurements of FeRh, La(Fe,Si)13 and the laves phases HoCo2 and DyCo2. With these measurements, we show the magnetic field dependence of X-ray Magnetic Circular Dichroism (XMCD), stray field, longitudinal and transversal strain and sample temperature. Furthermore we demonstrate the capability to measure XAS/XMCD and diffraction on a single grain inside this material.
We acknowledge financial support from DFG through CRC/TRR 270 HoMMage, the BMBF through project ULMAG and the ESRF by beamtime allocation.
References
[1] O. Gutfleisch et al. , Adv Mater, 23, 821 (2011)
[2] T. Gottschall et al. Nat Mater, 17, 929 (2018)
[3] F. Scheibel et al. Energy Technology, 6, 1397 (2018)
[4] K. P. Skokov et al., Appl. Phys. Rev. 10, 031408 (2023)
[5] A. Aubert et al., IEEE Trans. on Inst. Meas., 71, 1-9 (2022)