Thermal expansion and magnetovolume effects in the heavy-fermion systemCe2RhIn8

Abstract

We present the results of thermal expansion ␣(T), magnetostriction (H,T), and specific-heat C p (T) measurements made on the heavy-fermion antiferromagnet Ce 2 RhIn 8 . The effects of magnetic order are clearly evident as anomalies in ␣(T) at T N ϭ2.8 K and at T m ϭ1.65 K. C p (T) data indicate that the upper transition corresponds to the onset of long-range antiferromagnetic order while the lower transition involves only a subtle rearrangement of the ordered state. Both C p /T and ␣/T grow with decreasing temperature below 20 K in a manner consistent with Kondo renormalization. Kondo interactions appear to be responsible for the large electronic Grüneisen parameter which extrapolates to ⍀ e Ϸ48 as T→0, while the characteristic Kondo energy is T K Ϸ10 K as determined from the C p /T ratio at T N . Above 20 K ␣(T) is dominated by crystalline-electricfield ͑CEF͒ effects. The data are consistent with a CEF level scheme consisting of excited ⌫ 7(1) and ⌫ 6 doublets lying 71Ϯ6 K and 195Ϯ10 K above a ⌫ 7 (2) ground state. In the paramagnetic state (TϾT N ) the volume magnetostriction follows a simple scaling law, ϰ͓H/(TϩT )͔ 2 . The scaling parameter T ϭ5 K is consistent with the Kondo temperature determined from ␣(T) and C p (T) data. Analysis of (H,T) data also indicates that the magnetic and electronic energy scales associated with the Kondo state in Ce 2 RhIn 8 are equivalent. These thermodynamic data indicate that the physical properties of Ce 2 RhIn 8 result from competition between magnetic exchange, Kondo, and CEF interactions.

Evolution of magnetism in Pd-substituted Ce2RhIn8 single crystals

“…This approach considers the expression (1) which has been applied to the ferromagnetic CeNi x Pt 1-x series in the work of Blanco et al [22]. For Ce 2 RhIn 8 , we have obtained T K ≈ 6 K which is of the same order of magnitude as T K ≈ 10 K reported by Malinowski et al [4]. Further increase of the Kondo temperature of T K ≈ 7.5 K for the Pd concentration x = 0.15 and T K ≈ 12 K for x = 0.30 was observed simultaneously with an increase of the coefficient  and a decrease of the Néel temperature.…”

“…For x = 0, the pronounced peak at T N = 2.85 K reflects the wellknown transition of Ce 2 RhIn 8 to commensurate AF ordering [2]. At lower temperatures, additional anomaly at T LN = 1.45 K is observed which can be ascribed to a transition from the commensurate magnetic order existing between T LN and T N , to the ground-state incommensurate order reported in literature [4]. This order-to-order transition is absent in samples with x  0.1.…”

“…There are several methods of estimating the Kondo temperature and they may lead to different values of T K . However, usually a satisfactory agreement is achieved in general trends of the T K evolution within the series [4,22]. Being aware of these constraints in the present study, the value of T K was derived from the specific heat and from magnetic-susceptibility data.…”

High-magnetic-field thermal expansion and elastic properties ofCeRhIn5

“…9,10,11,12,16,18 Figure 5 shows α c at zero field and 18 T along the caxis in an extended temperature range. As previously observed 12 in Ce 0.6 La 0.4 RhIn 5 , the CEF-related negative peak around 25 K moves towards higher T when the field is increased.…”

“…Being that the spin-lattice coupling is a relevant issue in these Ce-based compounds, 9,12,16 in this work we investigate the magnetic effects on the volume and the elastic properties of CeRhIn 5 single crystals using high field linear thermal-expansion, magnetostriction and elastic constant measurements. Both first and second order transitions are observed in the magnetostriction and thermal-expansion coefficients giving rise to a field vs. temperature phase diagram similar to that obtained from specific heat experiments.…”