Nuclear Magnetic Resonance on Rare-Earth Nuclei in Re-Fe 2 Intermetallic Ccmpounds
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NUCLEAR MAGNETIC RESONANCE ON RARE-EARITH NJCLEI IN RE-Fe2 ITEPýPAILIC CCMPOUNDS Y. BERITIIER laboratoire de Spectrcanmtrie Physique, BP 53X, Grenoble C~dex, France R.A.B. DEVINE Physics Department, P.O. Box 248046, University of Miami, Coral Gables, Florida 33124 R.A. BUTERA Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 ABSTRACT NMR results in RE-Fe
2
internmtallic compounds at low
temperatures are reported. Using a spin-echo spectrometer in the U.H.F. range, hyperfine field parameters have been measured on 1 6 7 Er, 163Dy, 1 6 9 Tn and 159Tb at 1.4K. These cctnpounds have high Curie temperatures and the magnetic moment of the rare-earth, gJBi is nearly saturated. The value of the iron moment is also known from Mossbauer measurements and accurate data for the hyperfine field at the rare-earth site obtained from NM enables us to extract the internal field due to conduction electrons. INTRODUCTION Nuclear magnetic resonance (NMR) is a technique which enables us to proble macroscopically into the local environments in which nuclei find themselves. We have applied the technique to the study of rareearth/metallic intermetallic compounds in the ordered phase and it is primarily these measurements we shall discuss and with particular reference to the RE-Fe 2 laves phase compounds. Let us first consider the resonance phenomena in these coqpounds and look at the magnetic field seen by a rare-earth nucleus. In an ordered magnetic compound such as the RE-Fe 2 a RE nucleus sees a combination of magnetic fields. Let us call the total field seen by a rare-earth nucleus, HT.
A RE
ion has 4f electrons in an unfilled shell and as seen by the nucleus, these electrons will create a magnetic field. If the 4f shell is half filled (Gd 3+) a "spin only" type field is observed [1] typically of the order of -300 kOe. The negative sign arises because this field is created by a core polarisation term [1]. For RE ions having less than or more than half filled 4f shell there will be an orbital field produced. This field is in general large and may be several megagauss. This is by far the largest field seen by the RE nucleus and we call it H4 f.
450 There are two other fields we must consider. A magnetic ion immersed in a "sea" of conduction electrons interacts with the electrons via the exchange interaction [2]. In the case of the RE-Fe 2 ' s both the Fe and RE moments will polarise the conduction band electrons. Let us concentrate on a given RE nucleus and study the influence of the polarisation of the conduction bands. Firstly, all of the other RE ions and Fe ions will polarise the bands around them and via some form of spacially extended interaction (e.g. the RKKY [3] oscillations) this polarisation will be felt by the conduction electrons in the vicinity of the nucleus under study. Via the hyperfine interaction [4] a "transferred" field, HNN, will be seen. The ion whose nucleus is under study will also polarise the conduction electrons in its near vicinity and create a self-polarisation fiel
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