Magnetism in Metals A Symposium in Memory of Allan Mackintosh Copenhagen, 26–29 August 1996 Invited Review Papers Edited by D.F. McMorrow, J. Jensen and H. M. Rønnow Matematisk-fysiske Meddelelser 45 Det Kongelige DanskeVidenskabernesSelskab The Royal Danish Academy of Sciences and Letters Commissioner: Munksgaard · Copenhagen 1997 (cid:1)cDetKongeligeDanskeVidenskabernesSelskab1997 PrintedinDenmarkbyBiancoLunosBogtrykkeriA/S ISSN0023-3323 ISBN87-7304-287-0 Preface TheSymposiumonMagnetisminMetalstookplaceatTheRoyalDanishAcademy ofSciencesandLettersinCopenhagenon26-29August1996. TheSymposiumwas conceived by Allan Mackintosh with the aim of bringing together a wide group of international experts in the field to discuss and review recent developments and new perspectives in magnetism research. The Programme Committee comprised Allan, Leo Falicov, Jens Als-Nielsen, Ole Krogh Andersen and myself, but Allan steered us skillfully in the choice of invited speakers. 1996 was to be the year of his sixtieth birthday and he was proud that Copenhagen had been chosen as that year’sEuropeanCapitalCityofCulture. Hehadplannedtheprogramme,andhad secured generous financial support for the meeting. Alas,itwasnottobe. WeweregreatlysaddenedbythedeathofLeoFalicovin January 1995. The news of Allan’s sudden death in December 1995 was a further dreadfulshockforusall. WebelievedthatAllanwouldhavewantedustogoahead withthe Symposium,andJetteMackintoshencouragedustodoso. Iwasaskedto takeoverasChairmanoftheOrganisingCommittee: theprogrammewasmodified to include a memorial session on the first day, but otherwise was largely as Allan had planned. The splendid conference room of the Royal Danish Academy was filled with more than 80 participants: the memorial session was a deeply moving occasion with reminiscences and tributes to Allan from his brother Ian and son Poul, and fromsomeofhisclosestcollaboratorsandfriends,HansBjerrumMøller,OleKrogh Andersen, Jens Jensen,Kurt Clausenandmyself. The Symposium continuedwith the review talks, which are published in this volume. There were also a number of contributionspresentedasposters,whicharenotincludedhere. TheseProceedings begin with an obituary of Allan together with a list of his impressive range of scientific achievements and his publications. Allanhadalsoarrangedacomprehensivesocialprogrammefortheparticipants. The highlight of this was the magnificent Conference Banquet in Tivoli’s Nimb Restaurant. We alsotouredthe historic cathedralof Roskildeand the Viking Ship MuseumbeforevisitingRisøNationalLaboratory,ourhostsforanexcellentdinner. The Symposium received generous financial support from the Royal Danish AcademyofSciencesandLetters,theCarlsbergFoundation,theNovoFoundation, theDanishNaturalScienceResearchCouncilandRisøNationalLaboratory,which we gratefully acknowledge. iii The success of the Conference resulted from the collective efforts of many peo- ple. I would like to take this opportunity to thank Kurt Clausen and Ca Thi Studinski,wholookedafterallthefinancialaffairsandtheorganisationofthe par- ticipants,andJensAls-NielsenforthelocalarrangementsattheAcademy. Thanks go also to Des McMorrow, Jens Jensen and Henrik Rønnow for transforming the authors’ manuscripts into this volume as a permanent record of the Symposium dedicated to Allan’s memory. Keith McEwen iv Contents Allan Mackintosh, 1936–1995 ...................................... 1 Introduction: R.J. Elliott Developments in magnetism since the second world war.................................... 13 Rare earths and actinides: R.A. Cowley Magnetic structures of rare earth metals...... 35 and J. Jensen G.H. Lander Magnetism in the actinides................... 55 K.A. McEwen Crystal fields in metallic magnetism.......... 79 Thin films and superlattices: D.F. McMorrow Rare earth superlattices...................... 97 S.S.P. Parkin Magnetotransport in transition metal multi- layered structures............................ 113 R. Wu Recentprogressinfirstprinciplesinvestigations and A.J. Freeman of magnetic surfaces and thin films........... 133 Strongly correlated electrons: Y. Endoh Spin dynamics in strongly correlated electron compounds................................... 149 P. Fulde Routes to heavy fermions .................... 165 B. Johansson Itinerant f-electron systems.................. 185 and H.L. Skriver D.W. Lynch Photoelectron spectroscopy of cuprate super- and C.G. Olson conductors................................... 207 v T.E. Mason Neutron scatterring studies of heavy-fermion and G. Aeppli systems...................................... 231 G.J. McMullan The normal states of magnetic itinerant elec- and G.G. Lonzarich tron systems................................. 247 H.R. Ott Magnetism in heavy-electron metals.......... 259 G. Shirane Magnetism of cuprate oxides................. 281 General: M.S.S. Brooks Conduction electrons in magnetic metals ..... 291 B.R. Coles Dilute magnetic alloys........................ 315 E. Fawcett Spin-density-wave antiferromagnetism in the chromium system I........................... 325 D. Gibbs Two recent examples of x-ray magnetic scat- tering studies................................. 345 H. Ikeda Neutron scattering from disordered and fractal magnets...................................... 359 D. J´erome Magnetism and superconductivity sharing a common border in organic conductors........ 375 O. V. Lounasmaa Nuclear magnetism in copper, silver and rhodium...................................... 401 vi 0 MfM 45 1 Allan Roy Mackintosh, 1936–1995 AllanRoyMackintosh,whodiedon20December 1995asaresultofacaraccident in Denmark, devoted much of his life to the study of the behaviour of electrons in solids. He made major contributions to our understanding of the fundamental electrical and magnetic properties of the rare earth metals. In Denmark, where splendid traditions had been established in astronomy, atomic, nuclear and par- ticle physics half a century earlier, Allan Mackintosh will be remembered for his successful efforts in developing modern solidstate physics. Throughthe European PhysicalSociety and,morerecently, withinthe contextofthe EuropeanUnion, he strove to improve the quality and efficiency of physics research through interna- tional collaboration. BorninNottinghamon22January1936,he waseducatedatNottinghamHigh School and Peterhouse, Cambridge. His doctoral research was carried out in the CavendishLaboratory,underthesupervisionofSirBrianPippard,whereheinves- tigated the Fermi surface of metals, using ultrasonic attenuation methods. It was also in Cambridge that he met Jette, his Danish wife. On leaving Cambridge in 1960, he became Associate Professor of Physics at IowaState University. This movewastoshape the directionofhis future scientific career. The University’s Ames Laboratory had begun to make single crystals of the rare earth metals. The chemical properties of these elements are very similar, and consequently they had only recently been separated into pure form. However, their physical properties, particularly their magnetic behaviour, are very diverse and were, at that time, unexplored territory for the inquisitive physicist. Allan Mackintoshtookupthischallengeandsoonestablishedhimselfasaleadingexpert in this new field. His major contributions included the discovery (together with his student Dan Gustafson), by an elegant positron annihilation experiment, that the number of 4f electrons in cerium does not change significantly at the α–γ transition. ShowingthatCeisa4f bandmetaldisprovedthethenwidelyaccepted promotional model, and was an early contribution to heavy-fermion physics. In 1963, he spent a sabbatical at the Risø National Laboratory, in Denmark, 2 H. Bjerrum Møller et al. MfM 45 where a new research reactor had just become operational. Danish physicists led by Hans Bjerrum Møller were constructing a triple-axis neutron spectrometer to measure phonons in solids. Allan Mackintosh quickly realised the scientific poten- tialofapplyingthistechniquetomeasurespinwavesintherareearthmetals. This was the beginning of a most fruitful collaborationthat was to contribute substan- tially to our understanding of rare earth magnetism, and which lasted until the last hours of Allan’s life. In 1966, Allan Mackintosh moved permanently to Denmark and became Re- search Professor at the Technical University, Lyngby, where he remained until 1970. He brought with him from Ames not only precious rare earth crystals but also T. L. Loucks’ relativistic APW programs for performing electronic structure calculations. Allan used them to demonstrate the relevance of computing Fermi surfaces to describe magnetic ordering. He soon taught Danish students how to perform such calculations and asked them to compute the Fermi surfaces of the transition metals, whose complicated d-band sheets were currently being mapped out by the de Haas–van Alphen technique. It had been known only since 1964 that, unlike the localized 4f-electrons in the rare earth metals, the magnetic elec- trons in the 3d-transition metals contribute to the Fermi surface; the role of the Coulomb correlation between them was a much discussed topic. Allan had a deep understanding of the behaviour of electrons in metals, and a profound scepticism towards oversimplified theories. Leo Falicov was his life-long discussion partner and close friend. Allan’s work not only helped to establish the boundaries of the usefulness of density-functional calculations for d- and f-bands systems, but also inspired his students to develop new computational methods. In 1970 Allan became Professor of Experimental Solid State Physics at the University of Copenhagen. Soon afterwards, at the age of 35, he was appointed Director of the Risø National Laboratory. Prompted by the oil crisis, Denmark had embarked on a national debate about the development of nuclear power for electricity generation. In this frequently heated debate, Allan Mackintosh needed all his diplomatic skills to steer the discussion with factual rather than emotional persuasion. After1976,hereturnedtohisChairinCopenhagen,whereheremaineduntilhis death. He made many more important contributions to the understanding of the magnetism of the rare earths, which led to him being awarded (jointly with Hans BjerrumMøller)theprestigiousSpeddingPrizein1986. Heinspiredandmotivated all his collaborators and students, and his scientific papers, with their carefully constructed prose, are a pleasure to read. The culmination of his research was the publication (with Jens Jensen) of Rare Earth Magnetism, a superbly written exposition of the subject that has alreadybecome a classic text. His achievements were further recognised by his election in 1991 to Fellowship of the Royal Society