# Simultaneous Multi-Property Probing During Magneto-Structural Phase Transitions: An Element-Specific and Macroscopic Hysteresis Characterization at ID12 of the ESRF

Alex Aubert, Konstantin Skokov, Gabriel Gomez, Alisa Chirkova, Iliya Radulov, Fabrice Wilhelm, Andrei Rogalev, Heiko Wende, Oliver Gutfleisch,

Katharina Ollefs

► To cite this version:

Alex Aubert, Konstantin Skokov, Gabriel Gomez, Alisa Chirkova, Iliya Radulov, et al. Simultaneous Multi-Property Probing During Magneto-Structural Phase Transitions: An Element-Specific and Macroscopic Hysteresis Characterization at ID12 of the ESRF. IEEE Transactions on Instrumentation and Measurement, 2022, 71, pp.1–9. 10.1109/TIM.2022.3157001. hal-05074750

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https://cnrs.hal.science/hal-05074750v1

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# Simultaneous Multi-Property Probing During Magneto-Structural Phase Transitions: An Element-Specific and Macroscopic Hysteresis Characterization at ID12 of the ESRF

Alex Aubert<sup>ID</sup>, Konstantin Skokov<sup>ID</sup>, Gabriel Gomez<sup>ID</sup>, Alisa Chirkova<sup>ID</sup>, Iliya Radulov<sup>ID</sup>, Fabrice Wilhelm<sup>ID</sup>,
Andrei Rogalev<sup>ID</sup>, Heiko Wende<sup>ID</sup>, Oliver Gutfleisch<sup>ID</sup>, Fellow, IEEE, and Katharina Ollefs<sup>ID</sup>

**Abstract**— We present a new instrument for advanced magnetic studies based on the high field X-ray magnetic circular dichroism (XMCD) end-station developed at the beamline ID12 of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). It offers a unique possibility to measure simultaneously element-specific and macroscopic properties related to magnetic, electronic, and structural degrees of freedom of magnetic materials. Under strictly the same experimental conditions, one can measure the XMCD response, macroscopic magnetization, volume changes, and caloric properties of a magnetic material as a function of magnetic field (up to 17 T) and temperature (5–325 K). To illustrate the performance of this new instrument, we present a case study of an equiatomic FeRh alloy across the first-order magneto-structural transition. This development is the first step toward a new fully dedicated end-station based on a 7 T split-coil superconducting magnet with an additional capability to perform X-ray diffraction experiments.

**Index Terms**— Magnetism, magnetometry, phase transition, simultaneous probing, X-ray magnetic circular dichroism (XMCD).

## I. INTRODUCTION

WITH the increasing demand for new high technology and energy-efficient devices, multi-stimuli functional materials with strong interplay between their structural, magnetic, and electronic subsystems appear at the forefront of research in material science [1], [2]. They form a new family of promising materials for applications in different technological areas, like heat-assisted magnetic recording (HAMR),

thermal energy storage, novel spintronic devices, magnetic refrigeration, etc. In a first-order phase transition (FOPT) material [3], the changes caused by an external stimulus in one subsystem of the solid (e.g., change of magnetization induced by a magnetic field) also give rise to significant transformations occurring in other subsystems (e.g., expansion of the crystal lattice, change in electrical resistivity, heating of the sample, and so on). However, the contributions of the different subsystems are usually characterized independently and in different samples, environment, or even laboratories. This creates difficulties in assembling scattered pieces of a puzzle into one coherent picture, and this is probably one of the reasons why the coupling mechanisms of a magneto-structural transition remain till now poorly understood. Therefore, it would be highly appealing to develop a novel experimental approach which combines element-specific and macroscopic measurements performed under strictly the same conditions (e.g., temperature and magnetic field) on a single sample.

The use of an element-specific technique is fundamental to discern the contribution of each atomic species to the macroscopic behavior of the sample, which is possible by X-ray magnetic circular dichroism (XMCD). The XMCD signal is defined as the difference in the X-ray absorption spectra recorded with left and right circularly polarized photons while the sample magnetization is kept fixed. XMCD is inherently element selective since it originates from transitions of a core electron of an absorbing atom into the empty states given by electric dipolar and quadrupolar selection rules. Furthermore, derivation of magneto-optical sum rules [2], [3] has greatly strengthened the analysis of XMCD data, offering a unique capability of quantitative determination of the orbital and spin contributions to the total magnetic moment carried by the absorbing atom. It is important to underline that XMCD is a vectorial probe of magnetism, i.e., the signal depends on relative alignment of the X-ray helicity (photon propagation direction given by X-ray wavevector **k**) and the quantization axis given by an applied magnetic field, $\vec{k} \cdot \vec{B}$. In contrast to X-ray emission spectroscopy or nuclear resonance X-ray scattering (Mössbauer) spectroscopy, XMCD is averaged to zero when local atomic moments are oriented randomly with respect to the incident X-ray wavevector as in paramagnetic materials. In addition, XMCD is silent for antiferromagnetic (AFM) materials where no net magnetization is present and is also

Manuscript received November 21, 2021; revised January 26, 2022; accepted February 8, 2022. Date of publication March 15, 2022; date of current version March 29, 2022. This work was supported in part by the European Synchrotron Radiation Facility (ESRF) under Grant MA-4551, and in part by the German Federal Ministry of Education and Research (BMBF) under Grant BMBF-Projekt05K2019, and in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), under Project 405553726-TRR 270. The Associate Editor coordinating the review process was Hamed Hamzehbahmani. (Corresponding author: Alex Aubert.)

Alex Aubert, Konstantin Skokov, Alisa Chirkova, Iliya Radulov, Fabrice Wilhelm, and Oliver Gutfleisch are with the Functional Materials Group, TU Darmstadt, 64295 Darmstadt, Germany (e-mail: alex.aubert@tu-darmstadt.de; rogalev@esrf.fr).

Gabriel Gomez is with the Faculty of Physics, University of Duisburg-Essen, 47057 Duisburg, Germany, and also with European Synchrotron Radiation Facility, 38043 Grenoble, France.

Fabrice Wilhelm and Andrei Rogalev are with European Synchrotron Radiation Facility, 38043 Grenoble, France.

Heiko Wende and Katharina Ollefs are with the Faculty of Physics, University of Duisburg-Essen, 47057 Duisburg, Germany.

Digital Object Identifier 10.1109/TIM.2022.3157001
null when a ferro- or a ferrimagnetic ordering results in a domain structure with a random orientation of magnetic domains as it occurs in the absence of an applied magnetic field. The requirement of element-specific net magnetization implies the use of an external magnetic field and quite often low-temperature capabilities for XMCD measurements.

Regarding macroscopic measurements, typical properties involved in FOPT are related to changes in magnetization, volume, temperature, and resistivity. Recently, a setup called “MaRS” has been built in the Functional Materials Group at TU Darmstadt, showing its capability to measure simultaneously various macroscopic properties of magnetocaloric materials (i.e., magnetometry, dilatometry, and thermometry) [4]. This setup has been used to better understand the multistimuli-response of the FOPT La(Fe, Si)₁₃ system.

Based on the “MaRS” concept, we have developed a new instrument aiming at measuring on the same sample and under the same experimental conditions the element-specific magnetic properties with XMCD technique and the macroscopic properties using magnetometry, dilatometry, and calorimetry. The new instrument has been implemented at the high field XMCD end-station at the beamline ID12 of the ESRF, and greatly enhanced its capability to study magnetic materials featuring FOPT. The detailed description of the instrument is presented here. XMCD is measured using total fluorescence yield detection mode in backscattering geometry. As the standard VSM approach for measuring magnetization is not compatible with XMCD measurements, we adopted instead the Hall probe magnetometry method [5]. The performances of our new instrument are illustrated with the preliminary results obtained on a quasi-equiatomic FeRh alloy. FeRh is a well-known magnetocaloric material which exhibits an FOPT from the AFM to the ferromagnetic (FM) state upon heating [6], [7]. The magnetostructural transition is accompanied by changes in physical properties, in particular, magnetocaloric (MCE) effects and magnetostriction [8], [9]. Among materials with an AFM-FM transition near room temperature, FeRh represents a benchmark system for research on solid state refrigeration [10]–[13], and was thus chosen here for a proof-of-principle study. The XMCD signal was measured as a function of the magnetic field, at the $L_{2,3}$ edges of Rh and the K-edge of Fe, simultaneously with the stray magnetic field of the sample, magnetostriction and magnetocaloric effect by means of two strain gauges and a thermometer glued to the sample. This instrument is being developed in the framework of the “ULMAG—Ultimate MAGnetic characterization” collaboration and serves as a prototype for a future fully dedicated end-station. This new setup will also be implemented at the beamline ID12 of the ESRF and is expected to become a versatile experimental tool in magnetism research.

## II. SAMPLE PREPARATION AND PRE-CHARACTERIZATION

In this study, two samples were used to calibrate and test our device. First, pure nickel rod was commercially purchased (≥99.99%) from Sigma-Aldrich. The rod was cut to get different nickel disks of 6.35 mm diameter with various

thicknesses (0.5, 0.75, 1.5, and 3 mm). These Ni samples were mainly used to calibrate and demonstrate the viability of the magnetic sensor (the Hall probe) to measure the magnetization.

In addition, a quasi-equiatomic FeRh sample was initially induction melted to ensure a homogeneous sample using high purity elements (>99.9%), and then suction cast in a copper mold using arc melting. The sample was subsequently annealed at 1000 °C for 72 h, then quenched in water. The X-ray diffraction (XRD) pattern of the sample was obtained via a Bruker D2 diffractometer (with Cu-Kα₁ and Cu-Kα₂ wavelengths) at room temperature, and is shown in Fig. 1(a). The XRD analysis confirms that the sample has the cubic B2-FeRh phase (space group *Pm-3m*), with a lattice parameter of 2.993 Å. No other phases were observed with XRD. Fig. 1(b) shows the thermomagnetic curve of the sample for an applied field of 0.2 T, measured by vibrating sample magnetometer (VSM). Upon cooling, the sample shows AFM coupling below 250 K, whereas a temperature of 315 K is necessary to ensure the FM state of the sample on heating. During the transition (290–315 K upon heating and 290–250 K upon cooling), both AFM and FM phases coexist together [14].

## III. DESCRIPTION OF THE INSTRUMENT

### A. General Concept

A schematic of the prototype installed and developed at the ID12 beamline of the ESRF is shown in Fig. 2. The sample is fixed to an Al sample holder, which is screwed to a cold finger of a Helium constant flow cryostat. The incident circularly polarized X-rays are passing through an oblong hole of Si photodiode acting and hit the sample at normal incidence. X-ray fluorescence photons emitted by the sample are detected in backscattering geometry with the Si photodiode, which is mounted directly on the liquid nitrogen shield of the superconducting solenoid generating magnetic field up to 17 T. The macroscopic properties (magnetization, dilatometry, and thermometry) are measured by means of sensors directly attached to the sample. Photographs of the sample with the attached sensors are shown in Fig. 3. The sensors are connected to external instruments controlled via GPIB interface. One of the surfaces of the sample remains free and is used for the X-ray absorption spectroscopy (XAS) and XMCD measurement. Thus, with the current setup, we can probe under the same conditions and simultaneously the: (i) magnetization; (ii) magneto-volumetric; (iii) magnetocaloric changes; and (iv) XAS/XMCD as a function of the magnetic field (up to 17 T) and temperature (5-325 K). Each component of the setup is described in Sections III-B–III-E.

A similar prototype was built in our home laboratory in TU Darmstadt to test simultaneous measurement of macroscopic properties without X-ray beam, based on the same external devices. The latter was built based on the commercial resistivity option of the quantum design-physical property measurement System (QD-PPMS) with the external instruments controlled by the MultiVu software implemented in the QD-PPMS.
<figure><img src="image_2.png" /><figcaption>Fig. 1. (a) X-ray diffraction pattern of the FeRh sample and (b) magnetothermal curve of the FeRh sample for an applied field of 0.2 T measured by VSM (red line) and Hall probe (blue line).</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Fig. 2. Schematic of the prototype for simultaneous measurements of: (i) magnetic stray field using Hall probe; (ii) magnetovolume change; (iii) sample's temperature change; and (iv) XMCD signal, implemented at the beamline ID12 of the ESRF.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 3. Photographs of the FeRh sample on the aluminum holder with the different sensors attached to it.</figcaption></figure>

### B. XAS and XMCD at ID12 (ESRF)

Circularly polarized X-rays are generated by one of three helical undulators installed at the ID12 straight section of the ESRF storage ring, and covering the energy range from 2 to 15 keV. The beamline ID12 is equipped with fixed exit

Si (111) double crystal monochromator and is optimized for XMCD measurements at the K-edges of 3d transition metals, L₂,₃-edges of the 4d/5d transition metals and rare-earths, as well as at the M₄,₅ edges of actinides. The high field XMCD experimental station is based on a high vacuum 52 mm
cold-bore solenoid producing a magnetic field up to 17 T [15]. The magnet is equipped with two access ports along the field axis, one for the incoming X-ray beam (and detector insert) and another one for the sample cryostat. The coil is powered by a 15 V, 150 A high-resolution (20-bit) four-quadrant power supply with an integrated low-current option. This power supply is specifically designed to ensure a fast sweep ramping of 2 T/min. What is important for XMCD measurements is that the relative difference in the absolute values of the field for two opposite directions does not exceed ±5 × 10⁻⁵. This experimental station is also equipped with helium continuous flow cryostat that was built in-house. The cryostat was designed to be “amagnetic,” i.e., the absolute value of magnetic susceptibility of parts exposed to the magnetic field exceeding 1 T is of the order of 10⁻⁵ or less. The temperature of the sample can be set in the range 5–325 K with a stability of the order of 0.1%. The incident flux of the monochromatic X-rays at the sample is about 10¹² photons/sec. The spectra are measured using total fluorescence yield detection mode. This setup is a unique experimental platform for basic research in magnetism and the workhorse of the XMCD measurements at the ESRF beamline ID12 [16].

### C. Magnetic Stray Field

As our experiments imply the use of X-rays and a cold finger (see above), it limits the use of the standard VSM technique for magnetic measurements because the sample remains static. Thus, the magnetic properties are measured by means of a commercially available GaAs Hall probe (HP) positioned as close as possible to the surface of the sample (see Fig. 2). This permits to probe the stray-field produced by the sample, mirroring the magnetization of the sample at the surface. A current source (Keithley 6221) is used to generate an ac current of 1 mA at 970 Hz. The amplitude (1 mA) and frequency (970 Hz) are chosen to ensure the optimum measurement conditions in the full magnetic field range (0–17 T). The Hall voltage is measured using a lock-in amplifier (SR830 from Stanford Research Systems).

The Hall probe's dimension is 1 × 1 × 0.6 mm³ and its active area is 0.5 × 0.15 mm². The probe has a theoretical sensitivity of approx. 50 mV/T (@0.1 T and 100 mA) in a wide temperature range (1.5–373 K). The HP is embedded in the center of an aluminum sample holder using Stycast glue maintaining its surface as close as possible to the surface of the sample, as shown in Fig. 2. This configuration permits to measure the stray field in the same direction of the applied magnetic field and the X-ray propagation vector, without influencing the XMCD measurement (see Fig. 2).

### D. Magnetovolume Change

The relative length change of the sample is measured by means of two Vishay Micromeasurement strain gauges (model SK-06-031CF-350). The gauges are connected to a high precision multimeter (Keithley 2002) used in the four-terminal sensing mode to measure their resistance. Two strain gauges (1.5 × 1.5 mm²) are glued to the surface of the bulk sample. One permits to measure the length changes along

the direction of the applied magnetic field (δL/L∥) and the second one is used to measure the changes in the perpendicular direction (δL/L⊥).

### E. Magnetocaloric Change

The magnetocaloric effect is measured by a Cernox resistance thermometer (model CX-1050-BC) soldered directly on the surface of the sample. The resistance is measured with a high precision multimeter (Keithley 2002) in the four-wire resistivity mode. We can thus measure the variation of the sample's temperature (δT/T).

## IV. RESULTS AND DISCUSSION

### A. Magnetic Measurement in Stationary Sample

One of the main challenges is to accurately probe the magnetization of the sample without VSM, as the sample must remain static in the cryostat. For that, we have used an approach based on a Hall probe positioned as close as possible to the surface of the sample. The HP measures the magnetic stray field at its spatial position. Thus, it will measure the sum of two contributions, coming from: (i) the applied magnetic field $H_{app}$ and (ii) the dipolar field of the sample $H_{dip}$. To obtain the sample's contribution only, one must calibrate the Hall probe in order to properly subtract the linear contribution of the applied magnetic field from the total stray field measured by the Hall probe

$$ \mu_0 H_{dip} = \mu_0 H_{probe} - \mu_0 H_{app}. \quad (1) $$

An example of the calibration and corrected curves are shown in Fig. 4 for a nickel sample.

The HP does not measure the magnetization of the whole sample as in VSM, but rather the magnetic stray-field produced by the magnetized sample at the position of the HP. Therefore, the HP measurements are highly sensitive to the shape of the sample and position of the sensor, which makes difficult to recover the net magnetization of the sample for non-common shapes.

To demonstrate the difference between two techniques, we have measured the stray field produced by nickel disks with different thickness by using the HP and compared them with VSM measurements on the same sample, as shown in Fig. 5. Measurements are performed by applying the magnetic field along the axial direction of the disks. The saturated magnetic moment measured by VSM has a dependence on the volume (i.e., mass) of the sample. This is highlighted by the multiplication factor (displayed with an arrow) between two subsequent saturation magnetization values which are correlated with the increase in mass of the sample (shown in brackets). On the other hand, the saturation value of the dipolar field [see Fig. 5(b)] is not linear with the mass of the sample. In this case, the saturation value depends also on the geometrical aspect ratio thickness/diameter of the sample. In both techniques, we observed the increase in the slope at low applied field, due to the diminished effect of the demagnetizing field when increasing the thickness of the sample. In any case, the Hall probe measurements demonstrate
<figure><img src="image_5.png" /><figcaption>Fig. 4. Stray magnetic field measured by the Hall probe with (in red) and without (in blue) nickel sample and the corrected curve (in green).</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 5. (a) Magnetic moment of nickel disks with different thickness measured by VSM and (b) stray magnetic field measured for the same disks using the Hall probe. Measurements are performed by applying the magnetic field along the axial direction of the disks.</figcaption></figure>

an excellent capability to probe the magnetic state of samples
as thin as 500 µm.

In addition, the thermomagnetic curve of the FeRh sample
was measured by the HP technique to highlight its viability to
probe structural transition [see Fig. 1(b)]. The HP and VSM
techniques show similar behavior, which validates the accuracy
of the HP technique for such purpose.

B. *Simultaneous Measurement at Beamline ID12 of the ESRF*

The described instrument has been thoroughly tested and
the concept has been validated by investigating the FOPT
in FeRh alloy. The general schematic of the measurement
system is depicted in Fig. 2. With this setup, we are able
to study the transition either by varying the temperature or
by sweeping the applied magnetic field. In the present study,
we choose the second option, i.e., the sample is kept at a fixed
temperature and the FOPT is induced by applying a magnetic
field. Two main reasons explain this choice. Firstly, ramping
the magnetic field is faster than a temperature scan and this
is not a negligible advantage regarding use of the beamtime.
Secondly, the sweep rate at the high field XMCD end station is
as high as 33 mT/s and this is compatible with measurements
of the temperature change of the sample, i.e., magnetocaloric
effect. In case of a temperature sweep, the transition is slower

and the heat dissipated by the sample would be measured
less accurately. The measurements are performed at 245 K
to ensure the sample to be in AFM state no matter its
magnetic and caloric history. At this temperature, it exhibits an
AFM (low-temperature) to FM (high-temperature) transition at
around 5.5 T.

The X-ray-absorption near-edge structure (XANES) and XMCD spectra of the FeRh alloy, at the Rh L₂,₃ absorption edges and at the Fe K-edge, in FM state were measured at 245 K and under an applied field of 12 Tesla. All spectra are recorded using total fluorescence yield detection mode and reproduced on Fig. 6 as measured. For the experiments at the L-edges of Rh, we have used the first harmonic of the helical undulator HELIOS-II, whereas, for the experiments at the Fe K-edge, the second harmonic was preferred. High degree of circular polarization (ca. 95%) of the undulator beam was preserved downstream of the Si (111) double-crystal monochromator for the experiments at the Fe K-edge, but not for the experiments at the Rh L-edges. At this photon energy range between 3.0 and 3.2 keV, the Bragg angle of the monochromator is very close to 45°, resulting in a dramatic reduction of the circular polarization rate to only 11% and 5% at the Rh L₂ and Rh L₃-edges, respectively. Despite this fact, the XMCD signals at the Rh L-edges, probing
<figure><img src="image_7.png" /><figcaption>Fig. 6. X-ray fluorescence intensity and XMCD signal as function of photon energy at (a) Fe K-edge and (b) Rh L$_{2,3}$-edges.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 7. Field dependence of the stray field at the surface of the FeRh sample, with (a) its temperature and magnetostriction data measured simultaneously and (b) with XMCD(H) curves either at the Fe K-edge (scaled by a factor of 2.52) or at the Rh L$_{2}$-edge. These measurements are performed at 245 K. For the sake of clarity, the stray field detected by the Hall probes are shown on both panels.</figcaption></figure>

directly magnetic polarization of the Rh 4d states, are found bigger than the signal at the K-edge of Fe, which is due to polarization of the 4p states of Fe. The 4p magnetic moment is induced by a strong 3d-4p intra-atomic exchange and therefore XMCD at the Fe K-edge is, in fact, proportional to the total magnetic moment carried by Fe atoms. The negative (positive) sign of the XMCD signals at the L$_{3}$(L$_{2}$) absorption edge reveals the Rh 4d magnetic moment to be parallel to an applied magnetic field and, therefore, to the Fe magnetic moment. The same FM coupling of the Rh and Fe moments was found in the previous XMCD works on FeRh systems [17]–[19]. Full analysis of the element selective magnetic properties deduced from XMCD measurements will be given in a forthcoming paper.

The macroscopic measurements at 245 K of µ$_{0}$H$_{dip}$, δL/L, δT/T, and XMCD as function of magnetic field performed simultaneously at the ID12 beamline are shown in Fig. 7

(displayed in two separate graphs for better readability purpose). The macroscopic properties are shown in Fig. 7(a) whereas in Fig. 7(b) the stray field of the sample is plotted together with the XMCD signal acquired at the Fe K-edge and Rh L$_{2}$-edge. The XMCD signals are obtained at fixed photon energy, chosen at the maximum value of the corresponding XMCD spectra as indicated by the arrows in Fig. 6. For the Fe K-edge, the photon energy was fixed to 7121 eV whereas, for the Rh L$_{2}$-edge, it was fixed at 3146 eV. The AFM to FM transition is clearly seen from any of the properties measured, assessing the unique feature of our setup to investigate magnetostructural phase transitions simultaneously in the element selective manner (with XMCD) and macroscopically. This is the first proof of concept in the framework of the ULMAG collaboration, which is unique worldwide.

From a fundamental point of view, our findings permit to make a step further in the understanding of the FOPT in
FeRh, but also raise new questions. Regarding the macroscopic properties [see Fig. 7(a)], one can note that the change in length in the perpendicular direction (δL/L⊥) is delayed compared to: (i) the dipolar field and (ii) the change in length in the parallel direction (δL/L∥) of the sample. This feature has been observed in different FeRh samples and is tentatively attributed to the microstructural characteristics of the sample (texture, stresses, etc.) and is not considered as a measurement artifact. From the element-specific behavior [see Fig. 7(b)], the Fe K-edge and Rh L-edge display similar relative changes and behavior. In addition, one can note from Fig. 7(b) that the saturation of the XMCD signals is achieved at higher applied magnetic field than for the macroscopic stray field. Two hypotheses are currently investigated to understand the origin of such behavior. First, the X-rays are probing the near-surface layer of the sample, which could saturate at higher field than the overall bulk magnetization. However, it is not likely since the X-ray attenuation length [20] is fairly different at the Rh L-edges (≈1 µm) and at the Fe K-edge (≈5 µm) but the XMCD(H) curves are very similar. Second, it seems that the XMCD signals follow the perpendicular strain gauges behavior rather than parallel one. Further measurements are currently ongoing to understand these observations and all these fundamental questions will be addressed in a forthcoming paper.

V. PERSPECTIVES

In the near future, we aim at developing a more advanced
setup, “ULMAG–Ultimate MAGnetic characterization.” It will
also be implemented at the ESRF beamline ID12 with the
objective of measuring simultaneously and under strictly iden-
tical experimental conditions the following properties.

* Magnetization both macroscopically (with magnetometry) and in the element-specific manner (with XMCD).

* Changes occurring in the crystal lattice (X-ray diffraction) and in the sample as a whole (dilatometry).

* Thermal response of the material (magnetocaloric).

• Changes in resistivity.

Simultaneous measurements of micro/macroscopic properties
will be performed in a fully dedicated end-station based
on a 7 T superconducting split-coil magnet with variable
temperature insert allowing the temperature of the sample to be
varied between 5 and 400 K. Admittedly, the split-coil magnet
has a lower maximum field but has the advantage to allow the
insertion of a X-ray detector for X-ray powder diffraction mea-
surements. This will make a step further in the experimental
investigations of various subsystems in functional magnetic
materials.

This setup can be used to study any type of magnetic
transition where interplay between magnetic, structural, and
electronic subsystems of the solid is significant (spin-flop and
spin-flip transitions, itinerant electron metamagnetic transition,
first-order magneto-structural transition, and so on). In the
future, we also aim at expanding the material classes to be
investigated with the device (e.g., superconductors, multifer-
roics, topological materials, and so on). One should consider
that it is a unique way to study the relation between atomistic

features and macroscopic ones. At the moment, the samples
tested are in bulk form with typical geometry of 2 × 2 ×
4 mm³ as enough space should be available to attach all
the sensors. However, in the future, we do not exclude the
possibility to work with smaller samples and extend these
measurements to thin/thick films.

VI. CONCLUSION

We have developed a new instrument for advanced magnetic
studies based on the high field XMCD end-station installed
at the ID12 beamline of the European Synchrotron Radiation
Facility (ESRF). It offers a unique possibility to measure
under strictly the same conditions various properties, among
which are the magnetic stray field produced by the sample, the
parallel and perpendicular magnetostriction, the temperature
of the sample, and the XMCD signal, as function of field
(up to 17 T) and temperature (5–325 K). The advantage of
using Hall probes to sense magnetic properties is disclosed and
compared with the established VSM technique. In addition,
the capability of the device is demonstrated by investigating a
FOPT in a quasi-equiatomic FeRh sample. We showed that the
field-induced changes observed in dilatometry or in the XMCD
signal do not necessarily follow that of the magnetization.
These results can lead to a better fundamental understand-
ing of the first-order transition mechanism involving various
subsystems (magnetic, thermal, and so on). The setup can be
employed to investigate magnetic transitions and will serve as
a versatile tool to make a step further into the understanding
of different classes of magnetic materials.

ACKNOWLEDGMENT

The authors acknowledge the assistance of
Dr. Olga Shuleshova (IFW Dresden) in the sample preparation
and Dr. Neven Ukrainczyk in the XRD measurement.

REFERENCES

[1] O. Gutfleisch, M. A. Willard, E. Brück, C. H. Chen, S. G. Sankar, and J. P. Liu, “Magnetic materials and devices for the 21st century: Stronger, lighter, and more energy efficient,” *Adv. Mater.*, vol. 23, no. 7, pp. 821–842, 2011.

[2] O. Gutfleisch et al., “Mastering hysteresis in magnetocaloric materials,” *Phil. Trans. Roy. Soc. A, Math., Phys. Eng. Sci.*, vol. 374, no. 2074, Aug. 2016, Art. no. 20150308.

[3] J. Y. Law et al., “A quantitative criterion for determining the order of magnetic phase transitions using the magnetocaloric effect,” *Nature Commun.*, vol. 9, no. 1, pp. 1–9, Dec. 2018.

[4] D. Y. Karpenkov et al., “Pressure dependence of magnetic properties in La(Fe,Si)13 : Multistimulus responsiveness of caloric effects by modeling and experiment,” *Phys. Rev. A, Gen. Phys.*, vol. 13, no. 3, Mar. 2020, Art. no. 034014.

[5] F. Fiorillo, *Measurement and Characterization of Magnetic Materials*. Amsterdam, The Netherlands: Academic, 2004.

[6] C. J. Schinkel, R. Hartog, and F. H. A. M. Hochstenbach, “On the magnetic and electrical properties of nearly equiatomic ordered FeRh alloys,” *J. Phys. F, Metal Phys.*, vol. 4, no. 9, pp. 1412–1422, Sep. 1974.

[7] N. V. Baranov and E. A. Barabanova, “Electrical resistivity and magnetic phase transitions in modified FeRh compounds,” *J. Alloys Compound*, vol. 219, nos. 1–2, pp. 139–148, 1995.

[8] S. A. Nikitin, G. Myalikgulyev, A. M. Tishin, M. P. Annaorazov, K. A. Asatryan, and A. L. Tyurin, “The magnetocaloric effect in Fe49Rh51 compound,” *Phys. Lett. A*, vol. 148, nos. 6–7, pp. 363–366, Aug. 1990.

[9] M. R. Ibarra and P. A. Algarabel, “Giant volume magnetostriction in the FeRh alloy,” *Phys. Rev. B*, vol. 50, no. 6, pp. 4196–4199, Aug. 1994.
[10] M. Annaorazov, “COP of cooling cycles around the AF–F transition in FeRh based on experimental data,” *J. Alloys Compounds*, vol. 397, no. 1, pp. 26–30, 2005.

[11] A. Chirkova, K. P. Skokov, L. Schultz, N. V. Baranov, O. Gutfleisch, and T. G. Woodcock, “Giant adiabatic temperature change in FeRh alloys evidenced by direct measurements under cyclic conditions,” *Acta Mater.*, vol. 106, pp. 15–21, Mar. 2016.

[12] Y. Liu, L. C. Phillips, R. Mattana, M. Bibes, A. Barthélémy, and B. Dkhil, “Large reversible caloric effect in FeRh thin films via a dual-stimulus multicaloric cycle,” *Nature Commun.*, vol. 7, no. 1, Sep. 2016, Art. no. 11614.

[13] A. Chirkova et al., “The effect of the microstructure on the antiferromagnetic to ferromagnetic transition in FeRh alloys,” *Acta Mater.*, vol. 131, pp. 31–38, Jun. 2017.

[14] V. I. Zverev et al., “Peculiarities of the phase transformation dynamics in bulk FeRh based alloys from magnetic and structural measurements,” *J. Magn. Magn. Mater.*, vol. 522, Mar. 2021, Art. no. 167560.

[15] A. Rogalev and F. Wilhelm, “X-ray magnetic circular dichroism under high magnetic field,” *Synchrotron Radiat. News*, vol. 26, no. 6, pp. 33–36, Nov. 2013.

[16] A. Rogalev and F. Wilhelm, “Magnetic circular dichroism in the hard X-ray range,” *Phys. Met. Metallography*, vol. 116, no. 13, pp. 1285–1336, Dec. 2015.

[17] J. Chaboy et al., “X-ray magnetic circular dichroism probe of the rh magnetic moment instability in Fe1-xRhx alloys near the equiatomic concentration,” *Phys. Rev. B, Condens. Matter*, vol. 59, no. 5, pp. 3306–3309, Feb. 1999.

[18] A. Smekhova et al., “X-ray magnetic circular dichroism studies of FeRh nanoparticles,” *IEEE Trans. Magn.*, vol. 44, no. 11, pp. 2776–2779, Nov. 2008.

[19] V. M. T. S. Barthem et al., “Spin fluctuations of paramagnetic Rh clusters revealed by X-ray magnetic circular dichroism,” *Phys. Rev. Lett.*, vol. 109, no. 19, Nov. 2012, Art. no. 197204.

[20] B. L. Henke, E. M. Gullikson, and J. C. Davis, “X-ray interactions: Photoabsorption, scattering, transmission, and reflection at E=50-30,000 eV, Z=1-92,” *At. Data Nucl. Data Tables*, vol. 54, no. 2, pp. 181–342, Jul. 1993.

<figure><img src="image_9.png" /></figure>

**Gabriel Gomez** received the B.Sc. degree in physics from the National University of Colombia, Bogotá, Colombia, in 2007, and the M.Sc. and Ph.D. degrees in physics from the Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, in 2010 and 2014, respectively.

From 2015 to 2019, he worked as Post-Doctoral Researcher at the Neel Institute, Grenoble, France. During this time, he focused on the study of high-performance permanent magnet materials and contributed to the development of a high throughput production and characterization of compositionally graded films for magnetic applications. Since 2020, he has been a Post-Doctoral Researcher at the University of Duisburg-Essen, Duisburg, Germany, and a Visitor Scientist at the European Synchrotron Radiation Facility (ESRF), Grenoble. He received a scholarship from the National Council for Scientific and Technological Development (CNPq) of Brazil for his M.Sc. and Ph.D. degrees. His focus is on the development of a simultaneous X-ray magnetic circular dichroism (XMCD) and bulk properties dedicated device at the ID12 beamline of the ESRF, in collaboration with the Technical University of Darmstadt, Darmstadt, Germany.

<figure><img src="image_10.png" /></figure>

**Alisa Chirkova** received the B.Sc. and M.Sc. degrees in physics from Ural Federal University, Yekaterinburg, Russia, in 2007 and 2009, respectively, and the Ph.D. degree from TU Dresden, Dresden, Germany, in 2018.

She carried out Ph.D. studies on FeRh alloys at IFW Dresden, Dresden. From 2018 to 2021, she worked as a Post-Doctoral Fellow with the Functional Materials Group, TU Darmstadt, Darmstadt, Germany. Her current research interests comprise relationship of magnetic properties and microstructure in materials, as well as understanding of nucleation and growth processes during magnetic phase transformations.

<figure><img src="image_11.png" /></figure>

**Alex Aubert** received the Dipl.Ing. degree in electrical engineering from ESME Sudria, Paris, France, in 2015, the M.Sc. degree in physics and engineering of energy from ENS Paris-Saclay, Cachan, France, and the Ph.D. degree from the SATIE CNRS Laboratory, Department of Magnetic Materials for the Energies, Cachan.

After the Ph.D., he joined BCMaterial, Leioa, Spain, in 2018, as a Post-Doctoral Fellow to work on new permanent magnets in the European H2020 NOVAMAG Project. Since 2019, he has been a Post-Doctoral Fellow with the Functional Materials Group of Prof. Gutfleisch at the Technical University of Darmstadt, Darmstadt, Germany. His current research interest includes rare-earth free and rare-earth lean permanent magnets, correlation between material processing and magnetic properties, and design of novel experimental setup to characterize magnetic materials.

<figure><img src="image_12.png" /></figure>

**Iliya Radulov** received the M.S. degree from Sofia University, Sofia, Bulgaria, in 1998, and the Ph.D. degree from the Institute of Solid State Physics, Bulgarian Academy of Science, Sofia, in 2008.

From 2009 to 2011, he worked as a Post-Doctoral Fellow with the Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), Heraklion, Greece. From 2012 to 2021, he was with the Functional Materials Group, Technical University of Darmstadt, Darmstadt, Germany, and since 2021, he has been with the Magnetic Materials Group, Fraunhofer Research Institution for Materials Recycling and Resource Strategies, Hanau, Germany. His research interests include synthesis and characterization of new functional material system, as well as development of goal-specific apparatus for fulfilling this task.

<figure><img src="image_13.png" /></figure>

**Konstantin Skokov** received the Ph.D. degree in physics from Tver State University, Tver, Russia, in 1998.

He has been a Senior Researcher with the Functional Materials Group, Technical University of Darmstadt, Darmstadt, Germany, since 2012. He worked as an Assistant Professor with Tver State University from 1999 to 2008. From 2008 to 2012, he was a Scientist at the Leibniz Institute IFW Dresden, Dresden, Germany. His research interests are focused on the study of novel materials for permanent magnets and magnetocaloric application, as well as the development of unique scientific instrument for advanced characterization of magnetic materials.

<figure><img src="image_14.png" /></figure>

**Fabrice Wilhelm** received the Ph.D. degree from the Institute of Experimental Physics, Freie Universität Berlin, Berlin, Germany, in 2000.

His Ph.D. focused on the magnetic properties of ultrathin thin films, coupled trilayers, and 3d/5d multilayers studied by X-ray magnetic circular dichroism was awarded the Ernst-Eckhard-Koch prize. He joined the ID12 beamline team at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, in 2001. As a Beamline Scientist, his major scientific interests focus on the development and use of X-ray magnetic circular dichroism to study magnetic materials under multiple extreme conditions of high magnetic field, low temperatures, and high pressure.
<figure><img src="image_15.png" /></figure>

**Andrei Rogalev** received the M.S. and Ph.D. degrees from the Physics Department, Moscow State University, Moscow, Russia, in 1987 and 1992, respectively.

Since 1993, he has been working at the European Synchrotron Radiation Facility (ESRF)-The European Synchrotron, Grenoble, France, and became a Scientist in charge of beamline ID12 in 1998. His current research interests include synchrotron radiation instrumentation and applications of polarization-dependent X-ray spectroscopy in

studies of magnetism and its interplay with chirality.

**Oliver Gutfleisch** (Fellow, IEEE) is a Full Professor of the Technical University of Darmstadt, Darmstadt, Germany, a Scientific Consultant at Fraunhofer IWKS Hanau Materials Recycling and Resource Strategies, Hanau, Germany, and is running the external Max-Planck Research Group De Magnete at MPI, Düsseldorf, Germany, for Iron Research Düsseldorf. He has published more than 460 articles. His scientific interests span from permanent magnets for power applications to solid-state energy-efficient caloric cooling, ferromagnetic shape memory alloys, magnetic nanoparticles for biomedicine, with emphasis on tailoring structural and chemical properties on the nanoscale.

Dr. Gutfleisch was awarded an European Union European Research Council (EU ERC) Advanced Grant (Cool Innov) and is the speaker of the Deutsche Forschungsgemeinschaft (DFG) Cooperate Research Center 270 Hysteresis Design of Magnetic Materials for Efficient Energy Conversion.

<figure><img src="image_16.png" /></figure>

**Heiko Wende** received the Diploma degree in physics from the Free University of Berlin, Berlin, Germany, in 1995, the Ph.D. degree in element-specific studies at the synchrotron radiation source BESSY II, Berlin, in 1999. For his Ph.D. thesis, he was awarded the Ernst-Eckhard-Koch-Prize (Helmholtz-Zentrum Berlin).

His studies were supported by a scholarship of the Studienstiftung des deutschen Volkes. Already during his Ph.D. and subsequent habilitation, several research stays at the Brookhaven National

Laboratory, Upton, NY, USA, in collaboration with Prof. Y. U. Idzerda and at the University of Washington, Seattle, WA, USA, in collaboration with Prof. J. J. Rehr took place. Supported by a Heisenberg Fellowship from the Deutsche Forschungsgemeinschaft, he worked in the Group of Prof. O. Eriksson at the Uppsala University, Uppsala, Sweden, on the understanding of magnetic molecules. He accepted the call to the Faculty of Physics at the University of Duisburg-Essen, Duisburg, Germany, in 2007. He has been the Scientific Director of the Center for Nanointegration Duisburg-Essen (CENIDE), Duisburg, since 2018. He has led several projects funded by the European Union (Seventh Framework Program) as well as the Deutsche Forschungsgemeinschaft (DFG), such as projects in Collaborative Research Centers. He is currently project leader in the CRC 1242 "Non-Equilibrium Dynamics of Condensed Matter in the Time Domain," the CRC/TRR 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" as well as in the newly established CRC/TRR 270 "Hysteresis Design of Magnetic Materials for Efficient Energy Conversion." His research interests include magnetic hybrid systems, which he investigates using element-specific methods such as X-ray absorption spectroscopy at synchrotron radiation sources and free-electron lasers and Mössbauer spectroscopy. He works closely with research groups in theory, which use density functional theory to study electronic and geometric structures of hybrid systems.

<figure><img src="image_17.png" /></figure>

**Katharina Ollefs** received the Ph.D. degree in physics from the University of Duisburg-Essen, Duisburg, Germany, in 2012, building a new setup of X-ray detected ferromagnetic resonance.

She held a post-doctoral position at beamline ID12 at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, together with Andrei Rogalev. Since her undergraduate studies, she is exploiting X-ray absorption spectroscopy and imaging at various synchrotron radiation facilities and free electron lasers to study different solid-state

systems from dilute magnetic semiconductors to magneto-caloric materials. She is currently the Project Leader of the CRC 1242 "Non-Equilibrium Dynamics of Condensed Matter in the Time Domain" and CRC/TRR 270 "Hysteresis Design of Magnetic Materials for Efficient Energy Conversion."