Possible 4 f ⁷ 5 d ¹ Ground State of Gd Impurities in the Mixed-Valence Compound SmB ₆ , Observed with Electron Spin Resonance

Abstract

In SmB6 single crystals we observe a very anomalous ESR spectrum of Gd below 5 K. As far as we know, this is the first Gd spectrum, which cannot be explained by the electronic configuration Gd3+ 4f7. We discuss the appearance of the anomalous spectrum below 5 K by a trapped conduction electron, forming a formal divalent Gd 4f7 5d1 ground state. Above 6 K, where the conduction band of SmB6 becomes populated, we observe the usual Gd3+ Dysonian resonance as in conventional metals. The Hamiltonian of the 4f7 5d1 configuration, including a dynamic Jahn-Teller effect of the 5d electron, describes the complicated Gd spectrum reasonably well. The question, why SmB6, until now, seems to be the only host in which Gd3+ attracts a further electron, remains open.

NMR relaxation in the topological Kondo insulatorSmB6

“…Earlier measurements of Gd impurities in SmB 6 have been presented in Ref. 57. Due to the intermediate valence of SmB 6 the Sm ions in the bulk are not expected to resonate.…”

Spin-Glass Freezing and RKKY Interactions near the Metal-Insulator Transition in Amorphous Gd-Si Alloys

“…This is perhaps not surprising since the conduction electrons originate from s and d electrons of the Gd atom and are localized (or nearly localized) in part due to an exchange interaction with the 4f core electrons. There is only one reported case of Gd in a nontrivalent state, where an altered value for p is expected; in SmB 6 , Gd was reported to be in a divalent 4f 7 5d 1 state, with S 4 and reduced g value [15].…”

Revisiting the Possible 4f7 5d1 Ground State of Gd Impurities in SmB6 by Electron Spin Resonance

“…Aware of the G. Wiese et al reports [7,8], in this work we have measured ESR in Al-flux grown Sm 1−x Gd x B 6 samples in the range of 0.0002 ≤ x ≤ 0.004. We were capable of reproducing the X-band measurements at low temperatures reported previously [8] with the external magnetic field applied along the [100] direction.…”

“…G. Wiese, H. Schäffer and B. Elschner reported an electron spin resonance (ESR) study [7] in which a Hamiltonian including a 4f 7 5d 1 ground state and a dynamic Jahn-Teller effect was employed. This was investigated in great detail within a Diploma thesis [8], in which ESR measurements at 9.25 GHz (X-band) and various theoretical models were also reported.…”