Magnetic and Transport Properties ofROs₂Al₁₀(R=Pr, Nd, Sm, and Gd)

Abstract

We report on the synthesis and measurements of the magnetic susceptibility, electrical resistivity, and specific heat of ROs 2 Al 10 (R = Pr, Nd, Sm, and Gd). All compounds are isostructural with a Kondo semiconductor CeOs 2 Al 10 showing an unusual phase transition at T 0 = 28.6 K. For R = Pr, no magnetic transitions were observed down to 0.4 K, whereas compounds with R = Nd, Sm, and Gd undergo antiferromagnetic transitions at T N = 2.2 K, 12.5 K, and 18 K, respectively. Moreover, successive magnetic transitions occur for R = Sm and Gd. The resistivity of the compounds with R = Sm and Gd increases on cooling below T N due to the superzone-gap formation. The fact that T N = 18 K for R = Gd is lower than T 0 for R = Ce indicates that the phase transition in CeOs 2 Al 10 is not originated from the RKKY interaction alone but from the anisotropic hybridization of the 4 f state with conduction bands.KEYWORDS: ROs 2 Al 10 , antiferromagnetic transition, successive magnetic transition, superzone gap Cerium-based intermetallic compounds CeT 2 Al 10 (T = Ru and Os), which crystallize in the orthorhombic YbFe 2 Al 10 -type structure, 1, 2) have been studied extensively because of the occurrence of anomalous phase transition accompanying the formation of an energy gap.3-6) The transition temperature of T 0 = 27 K for T = Ru and 28.6 K for T = Os are exceptionally high for the antiferromagnetic (AFM) transition temperature in the Ce intermetallics. The formation of energy gap is manifested below T 0 by the upturn in the electrical resistivity and thermally activated behaviors in the magnetic susceptibility, specific heat, and spin-lattice relaxation rate of 27 Al-NMR/NQR. 5,7,8) In order to explain these features, charge density wave transition and spin-Peierls one have been expected.9, 10) However, the combined studies of powder neutron diffraction and µ + SR study evidenced the existence of AFM order of Ce 4 f moments whose values are 0.34 µ B /Ce for T = Ru and less than 0.2 µ B /Ce for T = Os.11, 12) However, it is still puzzling why the value of T 0 is so high despite the reduced Ce moments by the strong c-f hybridization effect. Interestingly, the c-f hybridization results in the formation of a pseudogap, which develops at the temperatures above T 0 .13) The fact that T 0 disappears suddenly at the critical pressure P C = 4 GPa for T = Ru and 2.5 GPa for T = Os is unaccountable by the Doniach phase diagram which assumes the competition between the c-f hybridization and RKKY interaction. 5,14) In this paper, we have synthesized and studied the magnetic and transport properties of ROs 2 Al 10 (R = Pr, Nd, Sm, and Gd) in order to estimate the strength of RKKY interaction in CeOs 2 Al 10 .Polycrystalline samples of ROs 2 Al 10 were prepared by arcmelting the stoichiometric amounts of the constituent elements under an Ar atmosphere. The obtained buttons were annealed at 1000• C for 3 days. Powder x-ray diffraction patterns indicated that the compounds ROs 2 Al 10 are isostructural with CeOs 2 Al 10 . The obtained lattice p...

Magneto-Electric Effect in Three-Dimensional Coupled Zigzag Chains

“…Indeed, the magnetic properties of NdFe 2 Al 10 , NdRu 2 Al 10 , GdRu 2 Al 10 , TbRu 2 Al 10 , DyFe 2 Al 10 , HoRu 2 Al 10 , and ErRu 2 Al 10 have been extensively studied. [35][36][37][38][39][40] For instance, J = 9/2 for Nd 3+ ions, J = 6 for Tb 3+ ions, and J = 8 for Ho 3+ ions lead to a large enhancement factor η. Third, for transition-metal ions, e.g.…”

Measurement of Crystal Field Excitations in NdT2Al10 (T = Ru and Os) by Raman Scattering

“…It has been known that the transition temperatures T * of Ce compounds are much higher than those expected from transition of Gd compounds following the de Gennes low. It is found that the transition temperatures of SmOs 2 Al 10 are also high [12]. Such high transition temperatures and successive transitions will suggest the existence of complicated interactions in the family.…”

“…Here, we will show all energy levels of crystal field states of Nd 3+ in NdRu 2 Al 10 and NdOs 2 Al 10 determined by Raman scattering measurements. Although the highest transition temperature is 2.4 K and 2.2 K for NdRu 2 Al 10 and NdOs 2 Al 10 , respectively [12,16], the Raman scattering spectra can be measured even above the transition temperatures.…”

“…Researches of the family have been expanded to other rare-earth compounds [12][13][14][15][16][17][18][19]. They reveal that many rare-earth compounds show successive transitions at low temperatures.…”

Effects of Ga and Si Substitutions for Al in CeRu2Al10 on the Unusual Antiferromagnetic Order in the Kondo Semiconducting State

“…In addition, T N exceeds that of isostructural GdT 2 Al 10 (T N =17.5 K for T=Ru and 18 K for T=Os) [17,18]. The magnetic susceptibility shows highly anisotropic behavior,  a > c > b , which originates from the crystalline electric field (CEF) effect.…”