Low temperature magnetism of the metallic pyrochlore oxide Pr_2+xIr_2−xO_7+δ

Abstract

Abstract. Pr 2 Ir 2 O 7 is a metallic pyrochlore compound which has been revealed to form a spin liquid phase by recent studies. Here we report results of magnetic and electrical transport properties of a newly synthesized polycrystalline sample of Pr 2+x Ir 2x O 7+ with excess Pr. A clear anomaly in the temperature dependence of the electrical resistivity is observed at 0.8 K, suggesting a phase transition into some sort of ordered state. IntroductionIt has been widely recognized that geometrical frustration due to certain lattice symmetries based on triangle motifs can be a source stabilizing novel states of matter [1,2]. Particularly, physics of spins residing on a three dimensional pyrochlore lattice consisting of a corner sharing network of tetrahedra has been extensively studied experimentally and theoretically [3,4]. A well-known example is a pyrochlore compound with the general formula A 2 B 2 O 7 (Fd-3m space group), in which both A and B sites individually form a pyrochlore lattice [5] Much attention has been currently devoted to pyrochlore Pr 2 Ir 2 O 7 , a rare example of a metallic frustrated spin system [9][10][11][12]. In this compound, Pr 3+ and Ir 4+ ions carry the localized frustrated magnetism and conduction electrons, respectively, providing a unique opportunity to investigate the correlation between frustrated magnetism and mobile electrons. Indeed, a single crystal study revealed that despite relatively high Weiss temperature of  20 K, the system exhibits no long-range order and instead forms spin liquid state at least down to T f = 110 mK, where a partial spin freezing was found. Besides, the Kondo effect is observed, indicating that the frustrated magnetism correlates with conduction electrons through the Kondo coupling [10]. Furthermore, a spontaneous Hall effect in the absence of uniform magnetization has been discovered in the spin-liquid phase [12]. This observation suggests that Pr 2 Ir 2 O 7 is the first example of a chiral spin liquid where time reversal symmetry is macroscopically broken without magnetic dipole order.In frustrated spin systems, an external perturbation such as magnetic field and chemical disorder often destabilizes a spin liquid state, and, as a result, a novel ordered phase might emerge. Here, we have investigated magnetic and electrical transport properties of a newly synthesized polycrystalline sample of Pr 2+x Ir 2x O 7+ with an off-stoichiometric composition, x = 0.4(3), and found a possible phase transition into some sort of ordered phase. An origin of the phase transition will be discussed.

Metal-Insulator Transition in Pyrochlore Oxide (Nd1−xPrx)2Ir2O7 (0.7 ≤ x ≤ 1)

“…For x = 0.95, a slight drop in electrical resistivity is observed at T O = 0.67 K. Interestingly, for x = 0.90, two anomalies are observed at 1.3 and 0.5 K. Next, we will discuss these transitions at x = 0.90 Figure 3 shows the reciprocal magnetic susceptibilities of (Nd 0.10 Pr 0.90 ) 2 Ir 2 O 7 in a magnetic field of 1 kOe. The effective magnetic moment of (Nd 0.10 Pr 0.90 ) 2 Ir 2 O 7 is estimated to be 2.55 µ B by Curie-Weiss fitting for data below 14 K. This value is in good agreement with 2.73 µ B for Ln = Nd and 2.68 µ B for Ln = Pr [16,19]. This results in the similar characteristics of the CEF ground state in both compounds.…”

“…For x = 1, a slight drop in electrical resistivity is observed at T O = 0.8 K, suggesting a long ranged order (LRO). It is reported that a polycrystalline sample of Pr 2 Ir 2 O 7 shows an anomaly at 0.8 K although the single crystalline sample shows spin liquid behavior without LRO [18,19]. However, the origin of anomaly at 0.8 K is not still clearly understood.…”

Comparative study of low-temperature x-ray diffraction experiments onR2Ir2O7(R=NdTakatsu1, Watanabe2, Goto3 et al. 2014Phys. Rev. B448200View full textAdd to dashboardCite

“…It is known that frustrated magnets often exhibit strong sample dependence due to the frustration among spin interactions and many-body effects. This tendency has also been found in pyrochlore oxides A 2 B 2 O 7 (A = rare earth ions, B = transition metal ions) [8][9][10][11]44,[47][48][49][50] , including NIO 8,10 and EIO 8,10,11 , as well as PIO 8,10,44 , where the distribution of nonstoichiometric concentrations such as x and y of A 2+x B 2−x O 7+y is thought to induce sample dependent physical properties 11,44,[47][48][49][50] . Even in our samples, we also observed a slight discrepancy in EIO for the previous results.…”

“…The prepared samples exhibit qualitatively the same behaviors of M/H, C P , and ρ as those of the previous reports (Figs. 2 and 3) [9][10][11]44,46 . We confirmed that the second-order phase transition of the MIT appear at T MIT = 34 K for NIO and at T MIT = 120 K for EIO (Fig.…”

“…Polycrystalline samples of NIO, EIO and PIO were prepared by a standard solid-state reaction 9,10,44 . The appropriate amounts of Nd 2 O 3 (99.99%, Rare Metallic Co., Ltd.), Eu 2 O 3 (99.99%, Rare Metallic Co., Ltd.) or Pr 6 O 11 (99.99%, Rare Metallic Co., Ltd.) and IrO 2 (> 99.9%, Tanaka Kikinzoku Kogyo K. K.) were mixed for 30-60 minutes and pressed into pellets.…”