Evidence of ferromagnetism collapse and valence instability in EuB₆ at high pressures

Rare earth hexaborides host several complex physical systems ranging from low temperature super conductors up to Kondo systems with proposed non-trivial topology. Among them all EuB₆ is singled out for ordering in a ferromagnetic manner with well reported puzzling properties such as a two-step magnetic transition below 15 K ^[1], large negative magnetoresistance^[2] and magnetic polarons up to 40 K ^[3]. Most recently it was shown that EuB₆ may host Weyl points nearby its Fermi level rendering new possibilities for non-trivial electronic behavior with proposed links to magnetization properties^[4]. In this work we structurally compressed EuB₆ crystals utilizing hydrostatic pressures up to 30 GPa and probed magnetic and electronic properties utilizing X-ray spectroscopy techniques such as X-ray Absorption Near Edge Spectroscopy (XANES), X-ray magnetic Circular Dichroism (XMCD) and Synchrotron Mossbauer Spesctroscopy (SMS). Our findings show evidences for ferromagnetic collapse above 20 GPa with accompanying mean valency increase within applied pressure range and no sign for structural phase transitions shown by X-ray diffraction. This opens possibilities for fine tuning topological properties utilizing external adjusting parameters in this compound.

¹ S. Sullow, I. Prasad, M. C. Aronson J. L. Sarrao, Z. Fisk D. Hristova, A. H. Lacerda, M. F. Hundley A. Vigliante and D. Gibbs PHYSICAL REVIEW B VOLUME 57, NUMBER 10 (1998).

² Manna, Rudra Sekhar, et al. "Lattice strain accompanying the colossal magnetoresistance effect in EuB 6." Physical review letters 113.6 (2014): 067202.

³ Merlin Pohlit, Sahana Rößler, Yuzo Ohno, Hideo Ohno, Stephan von Molnár, Zachary Fisk, Jens Müller, and Steffen Wirth. PHYSICAL REVIEW LETTERS 120, 257201 (2018)

⁴ Yuan, Jian, et al. "Magnetization tunable Weyl states in EuB6." Physical Review B 106.5 (2022): 054411.