Photon Factory Activity Report 2022 #40 (2023)

BL-3A/2020G665

Distorted helix in Eu-based magnetic semimetal EuZnGe
Takashi Kurumaji1,* and Taka-hisa Arima1,2

1 Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561,

Japan

2 RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan

1 Introduction
The search for new magnetic quantum materials
with emergent electrodynamic responses is essential
for future applications in spintronic technologies.
Europium-based semimetals are a group of materials
attracting growing interest due to the strong interplaybetween the conduction electrons and the underlying
magnetic moments of Eu2+. Recent material searches
along these lines have led to a rich series ofdiscoveries
highlightedbythegiant
magnetoresistance in a Zintl-compound Eu5In2Sb6 [1],and anomalous transport properties due to possible
topological electronic bands in EuCd2Pn2 (Pn = As,Sb) [2].
In this study, we first report the magnetic properties
of Eu-based semimetal EuZnGe, and clarify adistorted spiral spin structure [3].
2 Experiment
We performed the resonant x-ray scatteringexperiment of EuZnGe using a single crystal grownby Eu-Zn flux. The measurement was carried out at
BL-3A by using the horizontally polarized x-ray inresonance with Eu L2 absorption edge (7.615 keV).
The scattering plane was set to be (H, 0, L). The
samplewasloadedintoa
vertical-field
superconducting magnet with the b axis parallel to thefield direction.
3 Results and Discussion
We observe magnetic Bragg scattering in the (0, 0,L) scan as shown in Fig. 1(a). The scattering showsup around L = 7.5 – 7.6 with a double-peak feature
indicating unconventional incommensurate spin
structure. We find that the magnetic scattering showsa resonant feature in the energy dependence of theintensity (Fig. 1(b)), and disappears above themagnetic transition temperature.
The simple helical spin modulation with themodulation wavenumber q would show a single peakat (0, 0, 2n±q), where n is integers. The double-peakfeature with diffuse intensity in-between suggests thatthe random mixture of the distorted spin
configurations for q = 0.5 and 0.4. To clarify thepossible spin structure in EuZnGe, we simulate thediffraction intensity profile by the 5- and 4-sublatticespin configurations as shown in Fig. 2(a). We
successfully reproduce the intensity profile (Fig. 2(b)).

We measure the magnetic field dependence of thescattering
intensity
profile,andobserved
nonmonotonic q-change at the spin-flop-likemagnetic transition. This is hard to be reconciled withthe multidomain scenario for the nearly degenerate
two spin configurations, and support our mixed model.
Underlying mechanism to stabilize such an
unconventional spin structure is unclear at themoment. Possible candidate would be a competition
between the RKKY interaction and the hexagonal inplane anisotropy. Recently, related spin structures
have been reported in several Eu-based materials [45]. The future study is necessary to deepen theunderstanding of the unusual spin spiral structure in
Eu-based magnetic semimetals.

Fig. 1: (a) Intensity profile along (0, 0, L). (b) Energy
dependence of magnetic Bragg scatterings (cyan andyellow) and fluorescence (red).

Fig. 2: (a) Model of spin configuration for 5 and 4sublattice structures. (b) Simulated and observed
intensity profiles for the distorted spiral spin structurein EuZnGe.
Acknowledgement
We thank Hironori Nakao and Hajime Sagayama
for their collaboration of this study.
References[1] P. Rosa et al., npj Quantum Mater. 5, 52 (2020).
[2] Y. Xu et al., Phys. Rev. Lett. 126, 076602 (2021).

Photon Factory Activity Report 2022 #40 (2023)[3] T. Kurumaji et al., Phys. Rev. Mater 6, 094410(2022).
[4] S. X. M. Riberolles et al., Nat. Commun. 12, 999(2021).
[5] H. Takahashi et al., Phys. Rev. B 102, 174425(2020).
* kurumaji@edu.k.u-tokyo.ac.jp