Why the Co-based 115 compounds are different: The case study ofGdMIn5(M=Co,Rh,Ir

Abstract

The discovery in 2001 of superconductivity in some heavy fermion compounds of the RMIn5 (R=4f or 5f elements, M=Co, Rh, Ir) family, has triggered enormous amount of research pointing to understand the physical origin of superconductivity and its relation with magnetism. Although many properties have been clarified, there are still crutial questions that remain unanswered. One of these questions is the particular role of the transition metal in determining the value of critical superconducting temperature (Tc). In this work, we analyse an interesting regularity that is experimentally observed in this family of compounds, where the lowest Néel temperatures are obtained in the Co-based materials. We focus our analysis on the GdMIn5 compounds and perform density-functional-theory based total-energy calculations to obtain the parameters for the exchange coupling interactions between the magnetic moments located at the Gd 3+ ions. Our calculations indicate that the ground state of the three compounds is a C-type antiferromagnet determined by the competition between the first-and second-neighbor exchange couplings inside GdIn3 planes and stabilized by the couplings across MIn2 planes. We then solve a model with these magnetic interactions using a mean-field approximation and Quantum Monte Carlo simulations. The results obtained for the calculated Néel and Curie-Weiss temperatures, the specific heat and the magnetic susceptibility are in very good agreement with the existent experimental data. Remarkably, we show that the first neighbor interplane exchange coupling in the Co-based material is much smaller than in the Rh and Ir analogues due to a more two dimensional behaviour in the former. This result explains the observed lower Néel temperature in Co-115 systems and may shed light on the fact that the Co-based 115 superconductors present the highest Tc. I. INTRODUCTIONThe family of compounds RMIn 5 (M=Co, Rh, Ir), where R is a rare earth, presents a rich variety of electronic and magnetic properties ranging from heavy fermion behavior and anomalous superconductivity to complex magnetic states. These properties are closely related to the strong correlations on the R 4f electrons and to the quasi two-dimensionality of the Fermi surface. These materials crystallize in a tetragonal structure that can be viewed as alternating MIn 2 and RIn 3 planes stacked along the c-axis (see Fig. 1), where the role of the transition metal M connecting the RIn 3 planes is central to determine the stability of the low temperature phase.The most puzzling features occur in the Ce-based compounds which present heavy fermion behavior at T 20 K. Correlation effects induce an enhancement of the electronic specific heat coefficient up to 1000mJ/mol K 2 for CeCoIn 5 which is an ambient pressure superconductor below T C = 2.3K.1 CeIrIn 5 has its superconducting transition at T C = 0.4K while CeRhIn 5 is an antiferromagnet at ambient pressure with a Néel temperature T N = 3.8K.2 For P > P cr = 1.77GP a the antiferromagnetic state of CeRhIn 5 is rep...

Dilution effects in spin 7/2 systems. The case of the antiferromagnet GdRhIn5

“…This coupling represents the average of the J 0 , J 1 and J 2 terms. For GdRhIn 5 , J = 1.83 K, as determined by first principle calculations [26]. To fit the experimental data, here we used a slightly smaller J = 1.7 K, similar to what has been done in ref.…”

“…To fit the experimental data, here we used a slightly smaller J = 1.7 K, similar to what has been done in ref. [26].…”

Lattice specific heat for the RMIn5 (R=Gd, La, Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction

“…In the high temperature range T 150K the specific heat surpasses the value expected from the Dulong-Petit law (DP) value expected at high temperatures. The excess from the DP value cannot be explained by magnetic fluctuations [11] nor by the electronic contribution as the γ value in these materials does not exceed 7mJ/K 2 . We used Eq.…”

“…This makes them a good starting point to study the low temperature electronic and magnetic properties of the 115 series, and get insights about its more complex compounds. Interestingly, GdCoIn 5 has a more two-dimensional magnetic behavior than its Rh and Ir counterparts which leads to a lower Néel temperature [11]. This may explain the lower Néel temperatures observed for the Co based compounds across the 4f series, and help understand the higher superconducting critical temperature in the Co based Ce and Pu 115 compounds.…”

“…In order to properly describe the specific heat of these compounds, at least three contributions must be considered [12,11]: i) the lattice dynamics, ii) the electronic bandstructure, and iii) the magnetic interactions. We perform totalenergy ab initio calculations and obtain the phonon spectra and specific heat of magnetic and non-magnetic compounds of the 115 family.…”