Effects of Co doping on antiferromagnetic structure in
Introduction
The Ce-based heavy-fermion compounds ( and Co: -type tetragonal structure) are intensively studied for a rich variety of low-temperature properties ascribed to the interplay between antiferromagnetism (AF) and superconductivity (SC). shows an unconventional d-wave SC below the transition temperature [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 below 0.7 K, suggesting that the Pauli paramagnetic effect strongly affects the SC state [2], [4]. In addition, above 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 by tuning pressure p. At an incommensurate (IC) AF order appears below the Néel temperature , whose structure is proposed to be helical with a propagation vector of [7], [8], [9]. The AF phase is weakly suppressed by increasing p, and then the SC order develops above [10], [11], [12], [13]. It is found that merges with at , and the Fermi-surface properties change at [14], suggesting an existence of the AF QCP in this p range.
The characteristics of the AF and SC states in the mixed compounds have been investigated by means of specific heat, magnetization, resistivity measurements [15], [16]. It is revealed that is reduced with increasing x, and then approaches zero at the QCP: . The SC phase evolves above , suggesting the coexistence of these two states for . Recent elastic neutron scattering (ENS) experiments revealed that a commensurate (C) AF state with the wave vector of 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 with the entire x range, performed using both the unpolarized and polarized neutron sources.
Section snippets
Experiment details
Single crystals of 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 direction (with a typical size of ) 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 , 0.23, 0.43, 0.53, and 0.7 measured at (), where instrumental backgrounds were subtracted using the data at 5 K (). A set of satellite Bragg peaks due to the IC-AF order with a modulation of was observed at and 0.23. are estimated to be 0.295(3) and 0.297(3), respectively, which are the same as the value (0.297) of pure [8]. At and , new Bragg peaks ascribed to the C
Summary
Our ENS experiments for revealed that the IC-AF state with the structure is suppressed upon doping with Co, and the C and IC AF states simultaneously emerge in the intermediate Co concentrations. These results suggest that the AF correlations with the C and its neighbor modulations are significantly enhanced near the QCP: , and they may be tightly coupled with the evolution of the SC phase above . 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.
References (31)
Physica C
(1997)J. Phys. Condens. Matter
(2001)Phys. Rev. Lett.
(2001)J. Phys. Condens. Matter
(2004)Phys. Rev. B
(2002)Phys. Rev. Lett.
(2003)Phys. Rev. B
(2005)Phys. Rev. Lett.
(2000)Phys. Rev. B
(2000)Phys. Rev. B
(2003)