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Jang, Hoyoung,Friemel, G.,Ollivier, J.,Dukhnenko, A. V.,Shitsevalova, N. Yu.,Filipov, V. B.,Keimer, B.,Inosov, D. S. Nature Publishing Group 2014 NATURE MATERIALS Vol.13 No.7
Heavy-fermion metals exhibit a plethora of low-temperature ordering phenomena . Among these are the so-called hidden-order phases that, in contrast to conventional magnetic order, are invisible to standard neutron diffraction experiments. One of the structurally most simple hidden-order compounds, CeB<SUB>6</SUB>, has been intensively studied for an elusive phase that was attributed to the antiferroquadrupolar ordering of cerium-4f moments . As the ground state of CeB<SUB>6</SUB> is characterized by a more conventional antiferromagnetic (AFM) order , the low-temperature physics of this system has generally been assumed to be governed solely by AFM interactions between the dipolar and multipolar Ce moments . Here we overturn this established picture by observing an intense ferromagnetic (FM) low-energy collective mode that dominates the magnetic excitation spectrum of CeB<SUB>6</SUB>. Inelastic neutron-scattering data reveal that the intensity of this FM excitation significantly exceeds that of conventional spin-wave magnons emanating from the AFM wavevectors, thus placing CeB<SUB>6</SUB> much closer to a FM instability than previously anticipated. This propensity for ferromagnetism may account for much of the unexplained behaviour of CeB<SUB>6</SUB>, and should lead to a re-examination of existing theories that have so far largely neglected the role of FM interactions.
Zabolotnyy, V. B.,Fü,rsich, K.,Green, R. J.,Lutz, P.,Treiber, K.,Min, Chul-Hee,Dukhnenko, A. V.,Shitsevalova, N. Y.,Filipov, V. B.,Kang, B. Y.,Cho, B. K.,Sutarto, R.,He, Feizhou,Reinert, F.,Inosov American Physical Society 2018 Physical review. B Vol.97 No.20
<P>Samarium hexaboride (SmB6), a Kondo insulator with mixed valence, has recently attracted much attention as a possible host for correlated topological surface states. Here, we use a combination of x-ray absorption and reflectometry techniques, backed up with a theoretical model for the resonant M-4,M-5 absorption edge of Sm and photoemission data, to establish laterally averaged chemical and valence depth profiles at the surface of SmB6. We show that upon cleaving, the highly polar (001) surface of SmB6 undergoes substantial chemical and valence reconstruction, resulting in boron termination and a Sm3+ dominated subsurface region. Whereas at room temperature, the reconstruction occurs on a timescale of less than 2 h, it takes about 24 h below 50 K. The boron termination is eventually established, irrespective of the initial termination. Our findings reconcile earlier depth resolved photoemission and scanning tunneling spectroscopy studies performed at different temperatures and are important for better control of surface states in this system.</P>