Electron spin resonance ofGd3+andNd3+inLuInA4 (A=Cu,Ni)

Abstract

PHYSICAL REVIEW B VOLUME 60, NUMBER 19 15 NOVEMBER 1999-I Electron spin resonance of Gd 3ⴙ and Nd 3ⴙ in LuInA 4 „AⴝCu,Ni… P. G. Pagliuso and C. Rettori Instituto de Fi´sica ‘‘Gleb Wataghin,’’ UNICAMP, 13083-970, Campinas-SP, Brazil J. L. Sarrao, A. Cornelius, and M. F. Hundley Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Z. Fisk National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 S. B. Oseroff San Diego State University, San Diego, California 92182 共Received 6 January 1999; revised manuscript received 3 May 1999兲 Low-temperature (1.6 KⱗTⱗ60 K) data of electron spin resonance for Gd 3⫹ and Nd 3⫹ diluted in LuInA 4 (A⫽Cu,Ni) compounds are presented. The results are interpreted in terms of a density of states at the Fermi level built up of a single s band for the Cu-based system and a multiple (s and d) bands for the Ni-based system. The susceptibility and specific heat data show negligible electron-electron exchange enhancement for both compounds. For the Cu-based system the exchange interaction between the rare-earth (Gd 3⫹ and Nd 3⫹ ) local moment and the conduction electrons depends on the conduction-electron wave vector. 关S0163-1829共99兲02939-2兴 I. INTRODUCTION Electron spin resonance 共ESR兲 of rare-earths 共RE兲 impu- rities in metallic hosts has been widely used to study 共i兲 the exchange interaction between the impurity localized mag- netic moment and the conduction electrons, 共ii兲 band- structures effects of the host metal, 共iii兲 crystal-field effects, 共iv兲 hyperfine interactions, 共v兲 highly correlated electron sys- tems, and 共vi兲 superconductivity of the host metal. 1 The exchange interaction experienced by a RE ion impurity in transition metals 2,3 and intermetallic compounds 1,4 varies in sign and magnitude depending on the transition-metal ion. 1 Because of the stability of the Gd 3⫹ and Nd 3⫹ ions 4 f shell, the negative exchange integral is not associated with a covalent mixing mechanism. 5 It has been suggested that a negative effective exchange for RE impuri- ties in some d-band compounds is due to the lack of orthogo- nality between the 4 f and d-orbitals of the neighbor sites. 5,6 The purpose of this paper is to show that ESR of Gd 3⫹ and Nd 3⫹ in the LuInA 4 (A⫽Cu,Ni) compounds can provide a means to probe the band structure of these systems. We showed that the ESR data of Gd 3⫹ in LuInCu 4 共Ref. 7兲 and YInCu 4 共Ref. 8兲 could be explained in terms of a single s electronic-band contribution to the density of states at the Fermi level. Alternatively, we will show here that the ESR data of Gd 3⫹ and Nd 3⫹ in LuInNi 4 cannot be explained with a single band. We propose that the contribution of s and d electronic bands to the density of states at the Fermi level is required to explain the data. II. EXPERIMENT Single crystals of Lu 1⫺x RE x InA 4 (RE⫽Gd,Nd; A ⫽Cu,Ni; 0.0005⭐x⭐0.005 nominal) of cubic AuBe 5 PRB 60 共C15b, F43m兲-type structure 9 were grown from a flux of ex- cess InCu by the method described elsewhere. 10 The crystals were of cubiclike shape with typical sizes of 4⫻3⫻1 mm 3 . The ESR experiments were carried out in a Varian E line and a Bruker ELEXSYS X-band spectrometers, using a liquid-helium tail dewar 共1.6–4.15 K兲 and a helium gas flux 共4–60 K兲 adapted to a room-temperature TE 102 cav- ity. Dysonian lineshapes 11 with A/B⬇2.2(2) were always observed. These line shapes are characteristic of localized magnetic moments in a metallic host with a skin depth smaller than the size of the samples. In order to increase the ESR signal to noise ratio, powdered crystals were used in most of the ESR measurements. Experiments conducted in single crystals did not show any anisotropy that could be attributed to crystal-field effects. Susceptibility measure- ments were made in a Quantum Design dc superconducting quantum interference device 共SQUID兲 magnetometer. Spe- cific heat measurements were performed in a small-mass calorimeter system that employs a quasiadiabatic thermal re- laxation technique. 12 Samples used here ranged from 50 to 150 mg. III. EXPERIMENTAL RESULTS Figure 1 shows the specific heat for the LuInNi 4 com- pound in the temperature range of 2 KⱗTⱗ20 K. In the low temperature region, C/T increases linearly with T 2 as seen in the inset of Fig. 1. The fitting parameters, ␥ and ␤ , obtained from these data are given in Table I. The Debye temperature, ␪ D , is given in Table II. Figure 2 gives the magnetic susceptibility data for some of the Lu 1⫺x RE x InNi 4 (RE⫽Gd,Nd) crystals used in ESR experiments, corrected for the compound core diamagnetism. Using the effective magnetic moments, ␮ e f f ⫽7.94 ␮ B and ©1999 The American Physical Society