Field-dependent ordered phases and Kondo phenomena in the filled skutterudite compound PrOs₄As₁₂

Abstract

Electrical resistivity, specific heat, and magnetization measurements to temperatures as low as 80 mK and magnetic fields up to 16 T were made on the filled skutterudite compound PrOs4As12. The measurements reveal the presence of two ordered phases at temperatures below approximately 2.3 K and in fields below approximately 3 T. Neutron-scattering experiments in zero field establish an antiferromagnetic ground state <2.28 K. In the antiferromagnetically ordered state, the electronic-specific heat coefficient ␥ Ϸ 1 J͞mol⅐K 2 below 1.6 K and 0 < H < 1.25 T. The temperature and magnetic-field dependence of the electrical resistivity and specific heat in the paramagnetic state are consistent with single-ion Kondo behavior with a low Kondo temperature on the order of 1 K. The electronic-specific heat in the paramagnetic state can be described by the resonance-level model with a large zero-temperature electronic-specific heat coefficient that decreases with increasing magnetic field from approximately 1 J͞mol⅐K 2 at 3 T to approximately 0.2 J͞mol⅐K 2 at 16 T.heavy fermion ͉ Kondo effect ͉ antiferromagnetism T he compound PrOs 4 As 12 belongs to the family of filled skutterudites, which have the formula AT 4 X 12 , where A ϭ alkali metal, alkaline earth, lanthanide, or actinide, T ϭ Fe, Os, or Ir, and X ϭ P, As, or Sb. Because the ions reside in an atomic cage with a large number of X nearest neighbors, the hybridization between the lanthanide filler ion localized 4f states and the conduction-electron states is appreciable, often resulting in strongly correlated electron phenomena. In a recent article (1), we reported a study of the physical properties of single crystals of the filled skutterudite compound PrOs 4 As 12 between approximately 0.4 and 300 K by means of magnetization M, specific heat C, and electrical resistivity measurements. The previous study revealed that the compound exhibits two (possibly three) ordered phases below approximately 2.5 K in zero field and approximately 3 T at zero temperature from kinks in M as a function of magnetic field H and temperature T. Features in the (T) and C(T) data in zero field can be identified with transitions into the two ordered phases below 2.5 K. The magnetic susceptibility conforms to a Curie-Weiss law below approximately 20 K with an effective magnetic moment eff ϭ 2.77 B ͞formula unit consistent with a ⌫ 5 ground state in a cubic crystalline electric field and a cusp at approximately 2.5 K, indicative of antiferromagnetic (AFM) order. These results provide another example of the wide range of correlated electron ground states that are found in the Pr-based filled skutterudites, which include conventional (Bardeen, Cooper, Schrieffer) superconductivity (e.g., PrRu 4 Sb 12 ) (2), unconventional superconductivity (e.g., PrOs 4 Sb 12 ) (3, 4), heavy fermion behavior (e.g., PrFe 4 P 12 , PrOs 4 Sb 12 ) (5-8), antiferroquadrupolar order (e.g., PrFe 4 P 12 , PrOs 4 Sb 12 ), and magnetic order (e.g., PrFe 4 Sb 12 ) (9, 10). In this article, we report measurements of the te...

Strongly correlated electron phenomena in Pr-based filled skutterudite compounds

“…This striking difference in the response of the HFOP to Ru and Nd substitutions may reflect the tendency of Ru substitution to increase the CEF splitting between the Pr 3þ G 1 ground state and the G 5 first excited state, in contrast to Nd substitution, which dilutes the Pr ions but preserves the configuration of ions around the Pr site and does not affect the CEF splitting between the G 1 and G 5 states. compound PrOs 4 As 12 to temperatures of 80 mK and in magnetic fields up to 16 T [44,45]. Features in these measurements reveal the presence of two ordered phases for temperatures below 2:3 K and in applied fields below 3 T, which can be seen in the H-T phase diagram displayed in Fig.…”

“…7, which tabulates the type of behavior and temperature at which it occurs for each compound. The phenomena include heavy fermion behavior, magnetic order, quadrupolar order, BCS superconductivity, unconventional superconductivity, metalinsulator transitions, and unordered [5,44,45,[47][48][49][51][52][53][54]. The graphic illustrates the sensitivity of the ground state of the Pr-based filled skutterudite compounds to the transition metal and pnictogen atoms out of which each compound is composed.…”

Crystal structure, 139La NMR and transport properties of the As-based filled skutterudites LaOs4As12 and PrOs4As12

“…3 shows the temperature dependencies of the thermoelectric power measured along the [1 0 0] direction for LaOs 4 As 12 and PrOs 4 As 12 . A sharp peak at T = 2.15 K in the S(T) data for PrOs 4 As 12 (for more detail, see the upper inset) reflects the AFM transition observed in our previous experiments [1,2]. Furthermore, there are two pronounced anomalies in the paramagnetic state: a negative low-T minimum at about 16 K and a positive high-T maximum at ∼82 K. Such behaviour in S(T) is often found in Ce-based intermetallic systems (see, e.g., Ref.…”

“…The upper and lower insets show the low-temperature data for PrOs 4 As 12 and LaOs 4 As 12 , respectively. dence for PrOs 4 As 12 has a similar origin, since its χ dc (T) results reveal the presence of CEF effects [1,2]. For instance, the analyses of the χ dc (T) data in terms of a Pr 3+ ion in cubic O h symmetry yield a splitting as low as 15 K between a Γ 5 triplet ground state and Γ 1 singlet first excited state [1].…”

“…Very recently, we reported that PrOs 4 As 12 displays two ordered phases below ∼2.3 K for magnetic fields less than 3 T. Neutron-scattering experiments in zero field established an antiferromagnetic (AFM) ground state at T < 2.28 K [1,2]. The temperature and magnetic field dependence of the electrical resistivity and the specific heat in the paramagnetic state are consistent with a single-ion Kondo behaviour with a characteristic temperature of the order of ∼1 K. For better understanding the influence of 4f electrons on the physical properties of PrOs 4 As 12 , we have performed studies of its non-4f electron homologue LaOs 4 As 12 by means of the X-ray diffraction, 139 La NMR, dc magnetic susceptibility and thermoelectric power.…”