Elsevier

Physica B: Condensed Matter

Volume 404, Issue 17, 1 September 2009, Pages 2539-2542
Physica B: Condensed Matter

Effects of Co doping on antiferromagnetic structure in CeRhIn5

https://doi.org/10.1016/j.physb.2009.06.014Get rights and content

Abstract

We performed the elastic neutron scattering experiments on the mixed compounds CeRh1-xCoxIn5, and found that doping Co into CeRhIn5 dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of qh=(12,12,0.3) observed in pure CeRhIn5 is suppressed with increasing x, and new AF states with an incommensurate q1=(12,12,0.4) and a commensurate qc=(12,12,12) modulations simultaneously develop near the AF quantum critical point: xc0.8. These results suggest that the AF correlations with the qc and q1 modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above x0.4.

Introduction

The Ce-based heavy-fermion compounds CeMIn5 (M=Rh and Co: HoCoGa5-type tetragonal structure) are intensively studied for a rich variety of low-temperature properties ascribed to the interplay between antiferromagnetism (AF) and superconductivity (SC). CeCoIn5 shows an unconventional d-wave SC below the transition temperature Tc=2.3K [1], [2], [3]. It is revealed that applying magnetic field breaks the SC state via a first-order phase transition at the upper critical field Hc2 below 0.7 K, suggesting that the Pauli paramagnetic effect strongly affects the SC state [2], [4]. In addition, above Hc2 the non-Fermi-liquid behavior is observed in the temperature variations of the specific heat and the resistivity, which is considered to be due to a quantum fluctuation induced in the vicinity of an AF quantum critical point (QCP) [5], [6]. On the other hand, both the AF and SC phases are observed in CeRhIn5 by tuning pressure p. At p=0 an incommensurate (IC) AF order appears below the Néel temperature TN=3.8K, whose structure is proposed to be helical with a propagation vector of qh=(12,12,0.297) [7], [8], [9]. The AF phase is weakly suppressed by increasing p, and then the SC order develops above p=11.5GPa [10], [11], [12], [13]. It is found that Tc merges with TN at p1.9GPa, and the Fermi-surface properties change at p2.35GPa [14], suggesting an existence of the AF QCP in this p range.

The characteristics of the AF and SC states in the mixed compounds CeRh1-xCoxIn5 have been investigated by means of specific heat, magnetization, resistivity measurements [15], [16]. It is revealed that TN is reduced with increasing x, and then approaches zero at the QCP: xc0.8. The SC phase evolves above x0.4, suggesting the coexistence of these two states for 0.4x0.8. Recent elastic neutron scattering (ENS) experiments revealed that a commensurate (C) AF state with the wave vector of qc=(12,12,12) emerges in the intermediate x range [17], [18]. This implies that the nature of the magnetic correlation is changed by doping Co, and it may significantly affect the evolution of SC order. It is therefore interesting to investigate the AF structure in the wide x range. In this paper, we report on the ENS experiments for CeRh1-xCoxIn5 with the entire x range, performed using both the unpolarized and polarized neutron sources.

Section snippets

Experiment details

Single crystals of CeRh1-xCoxIn5 were grown by the In-flux method. To minimize the effect of the neutron absorptions by Rh and In, we prepared the rod-shaped samples along the tetragonal [11¯0] direction (with a typical size of 1.6×1.6×15mm3) for the neutron scattering experiments. The Co/Rh concentration x and its distribution in the sample were checked by means of the electron probe microanalysis (EPMA) measurements. We used the samples with the homogeneous distribution of x being achieved

Results and discussion

Fig. 1 shows the unpolarized ENS patterns at 1.5 K for x=0.05, 0.23, 0.43, 0.53, and 0.7 measured at Q=(12,12,1+ζ) (0ζ1), where instrumental backgrounds were subtracted using the data at 5 K (>TN). A set of satellite Bragg peaks due to the IC-AF order with a modulation of qh=(12,12,δ) was observed at x=0.05 and 0.23. δ are estimated to be 0.295(3) and 0.297(3), respectively, which are the same as the value (0.297) of pure CeRhIn5 [8]. At x=0.43 and 0.53, new Bragg peaks ascribed to the C qc=(12,

Summary

Our ENS experiments for CeRh1-xCoxIn5 revealed that the IC-AF state with the qh structure is suppressed upon doping with Co, and the C qc and IC q1 AF states simultaneously emerge in the intermediate Co concentrations. These results suggest that the AF correlations with the C qc and its neighbor q1 modulations are significantly enhanced near the QCP: xc0.8, and they may be tightly coupled with the evolution of the SC phase above x0.4. It is also found that the H dependence of the AF structure

Acknowledgments

We are grateful to M. Matsuura, K. Hirota, T.J. Sato, and H. Yoshizawa for the technical supports on the ENS experiments. M.Y. thanks N. Aso for the informative discussions. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

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