PHYSICAL REVIEW B 94, 014418 (2016) Exploring the complex magnetic phase diagram of Ce 2 PdGe 3 : A neutron powder diffraction and μSR study A. Bhattacharyya, 1, 2, * C. Ritter, 3, † D. T. Adroja, 1, 2 F. C. Coomer, 1 and A. M. Strydom 2, 4 1 ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon OX11 0QX, United Kingdom 2 Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa 3 Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble, France 4 Max Planck Institute CPfS, N¨ othnitzerstrasse 40, 01187 Dresden, Germany (Received 4 December 2015; revised manuscript received 28 June 2016; published 15 July 2016) The magnetic state of the tetragonal compound Ce 2 PdGe 3 , which crystallizes in the space group P 4 2 /mmc, a derivative of the α-ThSi 2 structure, has been investigated by magnetic susceptibility, heat capacity, muon spin relaxation (μSR), and neutron diffraction measurements. Heat capacity data indicate two separate magnetic phase transitions at T N 1 = 10.7 K and T N 2 = 2.3 K. The presence of bulk long-range magnetic order is confirmed by our μSR study below 11 K, where a drop of nearly 2/3 in the muon initial asymmetry and a sharp increase in the muon depolarization rate were observed. Neutron powder diffraction reveals that only one out of two Ce sites becomes magnetically ordered with magnetic propagation vector κ = (0) at T N 1 , adopting an antiferromagnetic arrangement of magnetic moments μ Ce 3+ = 1.78(1)μ B along the c axis. At T N 2 the second Ce site orders similarly, following the same magnetic propagation vector κ = (0), showing, however, at the same time a significant ferromagnetic component within the tetragonal basal plane. A second propagation vector, κ = ( 1 2 ,0, 1 2 ), appears concomitantly at T N 2 . DOI: 10.1103/PhysRevB.94.014418 I. INTRODUCTION The search for unusual physical phenomena in cerium, yt- terbium, and uranium intermetallic compounds [1–6] features in the broader dome of strongly correlated electron systems for both experimentalists and theoreticians, as they provide an ultimate ground for exploring and testing new models to un- derstand the complex phenomena such as spin glass behavior [7,8], Kondo effect [9], heavy fermions [10], unconventional superconductivity [11], intermediate valence state [12], and novel magnetism [13–15] shown by these systems. Numerous ground states were realized due to the competition between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and the Kondo interaction. Their study is important in order to understand the interplay between various order parameters involving spin and charge degrees of freedom, and their role in stabilizing new quantum phases of matter [16–20]. Novel ternary rare-earth intermetallic [21] compounds R 2 TX 3 (R = rare-earth element, Ce, U; T = transition-metal element, Cr, Mn, Fe, Co, Ni, Cu, Rh, Pd, Pt, and Au; X = Si, Ge, Ga, In) represent a remarkable branch of this research field due to their complex and intriguing magnetic structures and physical properties, as, for example, multiple magnetic transi- tions, disordered magnetism, Kondo effect, and heavy fermion behavior. Most of the R 2 TX 3 compounds crystallize in AlB 2 - type or derived AlB 2 -type structures, which is the important unit of numerous prototypical strongly correlated electron systems, which include CaBe 2 Ge 2 , ThCr 2 Si 2 , and BaNiSn 2 [22,23]. In R 2 TX 3 the random sharing of crystallographic sites by T and X atoms produces a varying environment around the R ions and causes an alteration in the RKKY mediated * amitava.bhattacharyya@stfc.ac.uk † ritter@ill.fr exchange interaction, which will enable the formation of a spin glass. Ce 2 NiGe 3 is a Kondo lattice system below room temperature where the electrical resistivity is attributable to the scattering from localized, unpaired cerium 4 f electrons, i.e., magnetic resistivity increases as the temperature is lowered, instead of steadily decreasing, as is expected from the thermal scattering of conduction electrons by lattice vibrations [24]. Among the R 2 TX 3 systems, there are many families catego- rized as R 2 NiGe 3 [25], R 2 PdSi 3 [26], R 2 RhSi 3 [27], R 2 AgIn 3 [28], and R 2 CuIn 3 [29]. Each family typically presents various magnetic ground states with complicated magnetic structures originating from distinctive crystal structures. Mentioned here can be, e.g., the uranium-based compounds U 2 MSi 3 [30], which show numerous unusual magnetic properties strongly related to the crystal structure of the sample where, e.g., for M = Pd, Pt, Au, Ir, and Rh, spin glass or cluster glass behavior is found [30]. Recently, Baumbach et al. [31] suggested that Ce 2 PdGe 3 exhibits a Kondo-driven hybridization between the f -electrons and the conduction electron states. Their band structure calculations reveal a substantial f -electron weight close to the Fermi energy and the Sommerfeld coefficient of the heat capacity (γ ≈ 50 mJ/mol Ce K 2 ) supports this point of view. Ce 2 PdGe 3 forms in a tetragonal structure with space group P 4 2 /mmc, which is a derivative of the α-ThSi 2 type structure [22,23]. In this structure, cerium occupies two different sites (2c,2f ) which have different local coordinations by Ge (4g) and Ge/Pd occupying the 4i site (Table I). The local symmetry of the Ce1 site ( 1 2 , 1 2 ,0) is “mmm” and Ce2 site ( 1 2 , 1 4 , 1 4 ) is “−4m2.” The symmetry is lower than cubic and hence the Ce 3+ J = 5/2 ground multiplet will split into three doublets for both of the Ce sites. In this paper we contribute a careful magnetic structure analysis in response to the need for this important information expressed in a previous work [31]. Our investigation on Ce 2 PdGe 3 includes dc susceptibility [χ (T )], 2469-9950/2016/94(1)/014418(7) 014418-1 ©2016 American Physical Society