Obituary: Professor Allan Mackintosh

Allan Mackintosh's work opened up a new era in the understanding of magnetism.

He devoted much of his life to the study of the behaviour of electrons in solids, and made major contributions to our comprehension of the fundamental electrical and magnetic properties of a fascinating group of elements, the rare-earth metals. He will also be remembered for his successful effort in stimulating solid state physics research in Denmark, just as Niels Bohr's efforts half a century earlier had given that country its splendid traditions in atomic and nuclear physics. Many of his former students now occupy leading academic and industrial posts in a variety of countries; his influence on the development of his subject has been both broad and deep.

Mackintosh was born in 1936, in Nottingham. He was educated at Nottingham High School and Peterhouse, Cambridge. His doctoral research was carried out in the Cavendish Laboratory, under Professor Sir Brian Pippard, where he investigated the Fermi surface of metals, a rapidly developing field of solid state physics.

Leaving Cambridge in 1960, he took the established route to the United States, and became Associate Professor of Physics at Iowa State University. This was to shape the direction of his future scientific career. The university's Ames Laboratory had begun to make single crystals of the rare-earth metals. The chemical properties of this group of 17 elements are very similar, and consequently had only recently been separated into pure form. However, their physical properties, particularly their magnetic properties, are very diverse and were, at that time, unexplored territory for the inquisitive physicist. Mackintosh took up the challenge and established himself as a leading expert in this new field.

In 1966, he spent a sabbatical at the Riso National Laboratory in Denmark, where a new research reactor had just become operational. Danish physicists led by Hans Bjerrum Moller were constructing a novel type of neutron spectrometer to measure how atoms vibrate in solids. Mackintosh realised the scientific potential of applying this technique to elucidate the dynamics of the magnetic moments on an atomic scale in the rare-earth metals. He had brought some single crystal specimens from Ames, and made the first measurements of their spin waves. This marked a significant advance in the study of magnetism.

Shortly afterwards, he moved permanently to Denmark. In 1970 he became Professor of Physics at the University of Copenhagen, and a year later was appointed Director of the Riso National Laboratory. Prompted by the oil crisis, Denmark had embarked on a national debate about the development of nuclear power for electricity generation. Mackintosh needed all his diplomatic skills to steer the discussion with factual rather than emotional persuasion.

After 1976, he returned to his Chair in Copenhagen, where he remained until his death. His contributions to the magnetism of the rare earths led to his being awarded, jointly with Moller, the Spedding Prize in 1986. He inspired his colleagues and students, and his careful prose makes his scientific papers a pleasure to read.

The culmination of Mackintosh's research was the publication in 1991, with Jens Jensen, of Rare Earth Magnetism, a superbly written exposition of the subject that has already become a classic text. In the same year he was elected a Fellow of the Royal Society.

Although research was always Mackintosh's priority, his leadership skills were much in demand: from 1971 to 1976 as Director of the Riso Laboratory, and from 1986 to 1989 of Nordita (the Nordic Institute for Theoretical Physics), with its close connections to the Niels Bohr Institute. A strong believer in the need for international collaboration, he was also President of the European Physical Society from 1980 to 1982.

Allan Mackintosh took great pleasure in music, travelling and his comprehensive collection of malt whiskies. He disguised his enjoyment of sport and physical activity behind a facade of feigned mediocrity. On hill-walking holidays, he divided his energies between humorous discourses as to the pointlessness of climbing the next hill, and making certain that he was the first to the top.

In later years, his keen interest in the history of physics led him to investigate the mutual influence of Rutherford and Bohr, two of the founding fathers of modern physics. In one of his last papers, he showed the contribution of the Cambridge physicist Charles Ellis to the discovery of the neutrino. It is symbolic of his interest in the past as well as the future of physics, that he spent the last day of his life (he died after a car crash) selecting experiments to be carried out in 1996 at Riso under an EU- financed programme, and then gave a eloquent seminar on the discovery of the neutrino some 60 years ago.

Allan Roy Mackintosh, physicist: born Nottingham 22 January 1936; Associate Professor, Iowa State University 1960-66; Research Professor, Technical University of Denmark 1966-70; Professor of Physics, University of Copenhagen 1970-95; Director, Riso National Laboratory, Denmark 1971-76; Director, Nordic Institute for Theoretical Physics 1986-89; FRS 1991; married 1958 Jette Stannow (one son, two daughters); died Roskilde, Denmark 20 December 1995.