Anomalous Kondo Effect and Ordered State in Heavy Fermion System SmOs₄Sb₁₂: Resistivity, Sb-NQR, and Magnetization Measurements under High Pressure

Abstract

We report resistivity, nuclear quadrupole resonance (NQR), and magnetization measurements under high pressures in a novel heavy fermion compounds SmOs4Sb12. The resistivity and nuclear spin-lattice relaxation rate 1/T1 show the coherent behavior below a characteristic temperature T * = 20 − 25 K at ambient pressure. Nuclear spin-spin relaxation rate 1/T2 was found to show a peak of electrical origin around T * . Some charge fluctuation is considered to play an important role in the Kondo effect of SmOs4Sb12. On the other hand, the magnetization at low temperature does not increase under pressures, although the transition temperature increases. The NQR signals are strongly suppressed around the transition temperature and vanishes at low temperatures. These suggest that the ordered state in SmOs4Sb12 is not simple ferromagnetism.

Magnetic-Field-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12

“…The double UDs so far only have been observed in NdOs 4 Sb 12 (4 f 3 ) and SmOs 4 Sb 12 (4 f 4 ), while LaOs 4 Sb 12 (4 f 0 ) and PrOs 4 Sb 12 (4 f 2 ) show single UD. It has been pointed out that the observations of double UDs are comparable to the 123 Sb-NQR measurements on ROs 4 Sb 12 (R = La-Sm), which show double or triple peaks in the temperature dependence of 1/T 2 for R = Pr-Sm due to some local charge fluctuation with a correlation time of ∼ 10 −6 sec, while LaOs 4 Sb 12 shows only a single peak 27).…”

Heat Capacity and ac-Susceptibility Measurements of SmOs4Sb12under High Pressure

“…The previous result of magnetization measurement up to 2.0 GPa showed similar tendency. 6) Existence of maximum at 0.8 GPa is suggestive in relation to the NFL behavior in the temperature dependence of resistivity observed in this pressure range.…”

“…creasing with increasing pressure further, indicating that the field-insensitive HF state is robust against pressure. 5,6) The increase of T C and the enhancement of heat-capacity jump at T C indicates that the application of pressure stabilizes the ordered state. On the other hand, the drastic reduction of χ max above 0.8 GPa suggests that the ordered state is not simple FM state.…”

“…In order to investigate the nature of the ordered state, we already reported the temperature dependence of magnetization under high pressure. 6) However, this measurement was less-precise unfortunately since the subtraction of background signal contributed from the pressure cell is difficult due to the small magnetization of SmOs 4 Sb 12 .…”

“…This feature is consistent with decrease of the coherence temperature T * , obtained from the resistivity and Sb-NQR measurements. 6) Though the residual γ value at the lowest temperature seems to increase slightly with increasing pressure, the careful measurement and the analysis are required for the judgment. In the previous resistivity measurement, the coefficient A in ρ = ρ 0 + AT 2 shows a broad peak around 1 GPa and de-…”