Exchange and crystal field effects in the ESR spectra ofEu2+inLaB6

Abstract

Electron spin resonance of Eu 2+ ͑4f 7 , S =7/2͒ in a La hexaboride ͑LaB 6 ͒ single crystal shows a single anisotropic Dysonian resonance. From the observed negative g shift of the resonance, it is inferred that the Eu 2+ ions are covalent exchange coupled to the B 2p-like host conduction electrons. From the anisotropy of the spectra ͑linewidth and field for resonance͒, we found that the S ground state of Eu 2+ ions experience a cubic crystal field of a negative fourth order crystal field parameter ͑CFP͒, b 4 = −11.5͑2.0͒ Oe, in agreement with the negative fourth order CFP, A 4 , found for the non-S ground state R hexaborides. These results support covalency as the dominant contribution to the fourth order CFP for the whole R hexaboride family.

Tuning of exchange by band filling in low-carrier-density magnet Eu(Gd)B6

“…Increasing of temperature in the paramagnetic phase of Eu 1− x Gd x B 6 results in a steep evolution of the g ‐factor to its high temperature value (Fig. a), which becomes closer to the Eu 2+ free ion value g = 1.993 with increasing of Gd content . At the same time, two linear temperature dependencies can be clearly identified for the Δ H ( T ) datasets (Fig.…”

“…a and 3b. The different signs of the g ‐shift relative to the free ion value are specific for dilute Gd 3+ (Δ g ≈ +0.018 ) and Eu 2+ (Δ g ≈ −0.009 ) ions in the metallic environment of LaB 6 . However, the change of the g ‐shift in Eu 1− x Gd x B 6 at 2 K, which evolves from Δ g ≈ −0.066 for x = 0.007 to Δ g ≈ +0.182 for x = 0.039 (Fig.…”

“…However, the change of the g ‐shift in Eu 1− x Gd x B 6 at 2 K, which evolves from Δ g ≈ −0.066 for x = 0.007 to Δ g ≈ +0.182 for x = 0.039 (Fig. a), is unexpectedly large for the dense matrix of the Eu 2+ ions and may reflect the strong modulation of internal FM and AFM fields under Gd doping . It is more surprising that there are no appreciable changes of the g ‐factor at the onset of magnetic order (Fig.…”

Slow crystalline electric field fluctuations in the Kondo lattice SmB$_{6}$

“…The absorption response with exchange narrowing effects due to the exchange interaction between the Gd 3+ local moment and the ce, is obtained by calculating the transverse dynamic susceptibility χ + (ω). Assuming no bottleneck relaxation effects, χ + (ω) can be approximated by [31][32][33][34]:…”

“…Experimentally, it is verified that most insulating materials present negative b 4 while conductors present positive ones. [34,50] To the best of our knowledge, SmB 6 is the first compound where negative and positive values of b 4 may coexist at a nanometer scale, with temperature playing the role of the control parameter. For the Kondo insulator SmB 6 , positive and negative values of the b 4 may indicate the presence of a heterogeneous phase where metallic and insulating regions coexist in this T -range as a consequence of a local loss of coherence between the hybridized d-ce and Sm-4f electrons due to the CEF fluctuations.…”