Stoner, Edmund Clifton
STONER, EDMUND CLIFTON
(b. East Molesey, Surrey, England, 2 October 1899; d. Leeds, England, 27 December 1968)
Edmund Stoner’s early years were marked by financial insecurity, since his father, Arthur Hallett Stoner, was a cricketer and later a cricket coach— a calling that assured neither regular nor long-term employment. Stoner’s mother, Mary Ann Fleet, encouraged her only child in his studies and was also the principal source of his interest in music. Yet early financial problems were not the only difficulties facing Stoner: throughout his adult life, and particularly during his student days, he suffered from diabetes and related ailments. Despite these disabilities his strong will enabled him to pursue an active career in teaching and research and also to engage in a range of administrative and committee work. He was elected to the Royal Society in 1937 on the strength of his research contributions to atomic theory, the theory of magnetism, and the theory of dense stars. Stoner had mild socialist leanings and was unattached to any religious denomination. He married Jean Heather Crawford in 1951; they had no children.
After attending Bolton Grammar School, Stoner entered Emmanuel College, Cambridge, in 1918 to study for the natural sciences tripos, and three years later he accepted a research studentship at the Cavendish Laboratory under Ernest Rutherford’s supervision. Although the Cavendish was a major center for experimental research and the 1920’s a particularly exciting period in its history, Stoner found experimental research uncongenial and his progress frustratingly slow. Moreover, his project was interrupted by a period in the hospital, and he was also disconcerted by Rutherford’s bullying manner. Partly in reaction to this inimical situation, he took an increasing interest in developments in theoretical physics, reading extensively in atomic physics and participating actively in the Kapitza Club, a select group that met regularly to discuss the latest innovations in theoretical physics. The resolution of his financial and career problems lay in turning from experimental to theoretical physics, and he achieved this transformation dramatically in 1924 when he proposed his hypothesis of the distribution of electrons in the atom. In the same year he secured a lectureship at Leeds University, where he stayed for the rest of his career, becoming professor of theoretical physics in 1939.
The problem in physics that confronted Stoner in 1924 emerged from Niels Bohr’s theory of the atom, in which the elliptical orbits of electrons were described by two quantum numbers, n (indicating the length of the ellipse’s major axis) and k (indicating its eccentricity), such that k could have any of the values 1, 2, . . ., n. In the early 1920’s there was much disagreement about the detailed distribution of electrons and about the physical meaning of the inner quantum number j, which Sommerfeld introduced to classify multiplet spectra (j = k - I, k - 2, -k + 2, -k + 1). Whereas Bohr had contented himself with guessing at the number of electrons in an atom having nk orbits, Stoner tried to discriminate down to nkj, levels, a task made particularly difficult by the uncertain significance of j. Stoner noticed that if the number of nkj electrons is 2j, the number of electrons associated with a given or the length of the nth period in the table of the elements. Stoner supported this distribution by offering evidence drawn from X-ray observations and from chemical, optical, and magnetic experiments.
The publication of his paper (Philosophical Magazine, 48 , 719–736) brought Stoner rapid recognition. His theory, however, was subsequently overshadowed by the exclusion principle of Wolfgang Pauli, who, exploiting Stoner’s insight and applying it to individual electrons, transformed it into a general and powerful analytic tool.
While his paper on electron distribution represents Stoner’s earliest and most spectacular success, he also worked extensively in several other problem areas. Soon after arriving in Leeds, he directed his research principally to the problem of applying quantum-theoretical ideas to explain the magnetic phenomena associated with matter, and was thereby able to adduce these explanations as further, impressive confirmations of quantum theory. Stoner played an important role in opening up this research field, with some three dozen of his papers specifically devoted to the theories of diamagnetism and para-magnetism in ionic salts and ferromagnetism in metals. Two of these papers deserve particular mention. In 1938 Stoner obtained, with Fermi-Dirac statistics based on the exclusion principle, the intrinsic magnetic properties of metals in which the electrons are in an unfilled energy band of standard form (Proceedings of the Royal Society of London, ser. A, 165 , 372–414). Ten years later, in a paper jointly authored by E. P. Wohlfarth, he suggested that the hysteretic properties of ferromagnetics of high coercivity could be accounted for by the existence of magnetically anisotropic single domain “particles” within their matrix (Philosophical Transactions of the Royal Society of London, ser. A, 240 [1948[, 599–642). Magnetism was also the subject of two of Stoner’s books, Magnetism and Atomic Structure (London, 1926) and Magnetism and Matter (London, 1934), the latter reflecting the new quantum mechanics and theory of electron spin. He also published a shorter introductory text. Magnetism (1st ed.. London, 1930; 4th ed., London, 1948), in the Methuen monograph series.
Among Stoner’s other research interests were the theory of specific heats and astrophysics, especially the theory of dense stars. In this and other areas, he made extensive and insightful use of Fermi-Dirac statistics. Stoner’s contributions to theoretical physics are all the more impressive when it is remembered that he received little formal training in mathematical techniques. Although his published work reflects his primary research interest in theoretical physics, he believed that theoretical investigations should be combined with a close acquaintance with experimental procedures and that research should not be divorced from teaching.
The only extensive biography of Stoner is L. F. Bates, “Edmund Clifton Stoner, 1899–1968”, in Biographical Memoirs of Fellows of the Royal Society, 15 (1969), 201–237, which includes a bibliography of Stoner’s publications. Stoner’s papers are preserved in the Brotherton Library, University of Leeds, and have been cataloged by the Contemporary Scientific Archives Centre (CSAC no. 6/73); there is also a handlist (Brotherton no. 62) of additional material. Stoner’s work on the distribution of electrons is discussed in J. L. Heilbron, “The Origins of the Exclusion Principle,” in Historical Studies in the Physical Sciences, 13 (1983), 261–310.