Why the Co-based 115 compounds are different: The case study of GdMIn5 (M=Co,Rh,Ir)

J.I. FACIO; D. BETANCOURTH; P. PEDRAZZINI; V.F. CORREA; V. L. VILDOSOLA; D.J. GARCÍA; PABLO S. CORNAGLIA

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

APS

Año: 2015 p. 144091 - 144097

0163-1829

The discovery in 2001 of superconductivity in some heavy fermion compounds of the RMIn 5 (R = 4f or5f elements; M = Co, Rh, Ir) family, has triggered an enormous amount of research into understanding thephysical origin of superconductivity and its relation with magnetism. Although many properties have beenclarified, there are still crucial questions that remain unanswered. One of these questions is the particular roleof the transition metal in determining the value of critical superconducting temperature (T C ). In this work, weanalyze an interesting regularity that is experimentally observed in this family of compounds, where the lowestN ́eel temperatures are obtained in the Co-based materials. We focus our analysis on the GdMIn 5 compoundsand perform density-functional-theory-based total-energy calculations to obtain the parameters for the exchangecoupling interactions between the magnetic moments located at the Gd 3+ ions. Our calculations indicate thatthe ground state of the three compounds is a C-type antiferromagnet determined by the competition betweenthe first- and second-neighbor exchange couplings inside GdIn 3 planes and stabilized by the couplings acrossMIn 2 planes. We then solve a model with these magnetic interactions using a mean-field approximation andquantum Monte Carlo simulations. The results obtained for the calculated N ́eel 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 muchsmaller than in the Rh and Ir analogs which leads to a more two-dimensional magnetic behavior in the former.This result explains the observed lower N ́eel temperature in Co-115 systems and may shed light on the fact thatthe Co-based 115 superconductors present the highest T C .