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JOHN HASBROUCK VAN VLECK March :13, 1899-October 27, 1980 BY P. W. ANDERSON JOHN HASBROUCK VAN VLECK was the most eminent American theoretical physicist between }. Willard Gibbs and the postwar generation. He has often been characterized as the "father of modern magnetism," but his influence was in fact much wider: He played a vital role in establishing the modern fields of solid-state physics, chemical physics, and quantum electronics. Many generations of students were in- fluence(1 by his unique teaching style, and he made important administrative contributions at a crucial time in the history of Harvard University. FAMILY AND EARLY YEARS The Van VIeck family is of the patrician Dutch stock that has given the nation three presidents, among other eminent citizens. "Van" (as he was always known) was prouc! of his ancestry, which had been tracer! by an aunts to prosperous burghers of Maestricht in the sixteenth century. One of the family, Tielman Van VIeck, was an eminent citizen of the Dutch colony of Nieuw Amsterdam and founded Jersey City. Van's immediate family was very distinguished academi ' More details will be found in The Royal Society memoir by B. Bleaney. 501

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502 BIOGRAPHICAL MEMOIRS cally. His grandfather, John Monroe Van VIeck, was profes- sor of mathematics and astronomy at Wesleyan University in Micictletown, Connecticut, from IS53 to 1904, serving as act- ing president on two occasions. John Monroe's brother, Jo- seph Van VIeck, a successful New Jersey businessman, do- nated an observatory to Wesleyan in his honor. At the dedication ceremony in ~ 9 ~ 6, his son, E. B. Van VIeck, spoke anc! the young I. H. Van VIeck unveilecI the memorial plaque. All of John M. Van VIeck's four children were mathema- ticians, including Van's father Edward Burr Van VIeck (~863-19431. E. B. Van VIeck took a doctorate at Gottingen in IS93, taught for two years at Wisconsin, and then went to Wesleyan ~895-!905~. He marriec! Hester Raymond of MidcIletown in IS93, ant! here John Hasbrouck Van VIeck, his only chilcI, was born on March 13, TS99. From 1905 to 1929 Edward Burr Van VIeck was professor of mathematics at the University of Wisconsin in Madison, Wisconsin, where the mathematics building is named Van VIeck Hall in his honor. He was eminent in his field anct highly respected at Wisconsin. He was a member of NAS, president of the Amer- ican Mathematical Society, and recipient of four honorary degrees. His lectures were notecT for their formal clarity. The E. B. Van VIeck home was a cultivated anc! a pros- perous one, since he inherited a portion of his uncle's for- tune. He built up a notable art collection, especially of Japa- nese woodblock prints but also of other objects of beauty. It is said that a number of the prints were acquired from Frank Lloyd Wright. They were collected (luring the building of the Imperial Hotel and sold to repay debts. Edward Burr and his wife Hester react voraciously and traveler! widely, so that "the galleries, churches, and mountains of Europe were equally familiar." In this atmosphere Van absorbed his inter- est in travel and his deep cultivation very naturally. Except for a few periods spent cluring his father's sabbat

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JOHN HASBROUCK VAN VLECK 503 icals in schools or kindergartens abroad, Van was eclucatect in the Madison public schools and went directly on to the University of Wisconsin. He did not recall any particular par- tiality toward science or mathematics as a boy, nor did his father make a special effort to interest him in advanced topics of mathematics, except for advising him to be sure to take mathematics through calculus in college. Reading his own remarks about this period of his life, one has the impression of a very normal boy with a rather matter-of-fact precocity. His interest in American football began early at Wisconsin, and he claimed that the Wisconsin song"On Wisconsin" was first sung at his first game in 1909 (information on this is containec! in an article of his on the history of football songs). He played in the Wisconsin marching band from 1916 until 1918 ~ his instrument is not recorclecI, but it was probably the flute, which he playocT later as a young assistant professor. His well-known interest in railroads began early: It was when he was about seven that he first spent a period of recupera- tion on one of his parents' European trips learning the rel- evant railroad schedules, and thereafter the family never again hart to consult a timetable. In college, an early interest in French was turner! off by his self-confessed "miserable" accent, anc! in geology by the obtuseness of a professor who "required all triangles to be solved graphically." In fact, until late in his college career, Van seems to have seen himself as a bit of a dilettante. His youthful preference tract been not to go into the academic life, and he recordecI in his reminiscences that "serious young men took engineer- ing rather than math or physics, where most of the students were girls." Just as he rebelled at solving triangles graphically, he evacled the physics senior thesis involving experimental work, including, worst of all possible fates, glassblowing by joining a debating team ant! arguing successfully against the government ownership of railroads. His states! reason (in

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504 BIOGRAPHICAL MEMOIRS "Reminiscences of the First Decade of Quantum Mechanics," 1971) for taking physics was the otherwise light course load and the iclea that mathematics would involve him in his fa- ther's courses, which would not be "cricket." He click, however, make Phi Beta Kappa in his junior year, so one is permitted a great deal of skepticism about the rather frivolous motiva- tions he gives for his choice of careers. ~ note also the inclu- sion of an "unlisted reacting course in Moliere" in the accel- eratec! program he finally completed-surely not a common . ,% 1 (J ~ ~ ' interest tor a young scientist in the Middle West. EARLY CAREER IN PHYSICS Van's consciousness of physics seems to have been first raised by the experience of a course on kinetic theory taken from L. R. Ingersoll in his third year at Wisconsin. He was not well prepared because he had put oR the calculus to this same year, but he sat near Warren Weaver who was taking the course (though on the junior faculty, and was a very vocal critic of the textbook used. This stimulates! Van's interest enormously. In the next year he took a course from Professor March on dynamics that was his introduction to genuine theoretical physics and showed him very clearly the course of his future career. A fortunate accident took him to Harvard for the last semester of the 1919-20 college year: His father was spencl- ing a sabbatical there, anti urged him to finish up at Wiscon- sin in three-anct-a-half years and come take courses at Har- vard. He started out with three courses in math and physics and one in railroad administration. This latter convincer] him that he "would not get on very fast in the railroact business." The courses that influenced him positively were by Bridgman anct Kemble. He felt Bridgman's operational philosophy, while not explicitly stated, was very much implicit in the at- titucle to physics that he acquired, while Kemble was one of

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JOHN HASBROUCK VAN VLECK 505 two or three teachers in the Unitecl States concerned about quantum theory. He was influenced negatively as well by a formal mathematical course in differential equations, a re- placement for his father's course, which he had been unwill- ing to take; this acIdecI to his lifelong distaste for empty for- malism. Thus, almost without conscious decision, he found him- self a full-fledged Ph.D. student at Harvard. He quickly com- pleted the requirements for an M.A. (1921) and finisher] a Ph.D. thesis uncler Kemble (19221. He stayer] on as instructor with Kemble for one more year, leaving for Minnesota in 1923. EARLY DAYS OF THE QUANTUM THEORY: HARVARD (1920 - 23) AND MINNESOTA (1923-28) His thesis topic attacked one of the truly knotty problems of the old quantum theory: the attempt to come up with a method of quantization that wouIcl give reasonable results for the helium atom. Once the hydrogen atom was more or less dealt with, anti simple harmonic motion unclerstoocI with De- oye's anti Planck's laws, the next stage was clearly more com- plex atoms. At about the same time, several European phys- icists were attempting the problem, anti Van's paper was essentially equivalent to results of Bohr, Kramers, and Kronig. In short orcler there followed a sequence of papers on various aspects of spectroscopy using the old quantum theory, and then a book, Quantum Principles and Line Spectra, finished in late 1925. During the Harvard years, Van was in constant touch with John Slater, who finished a mostly experimental thesis with Bridgman at about the same time, and then left for Copen- hagen to work for a year with Bohr. I think it is fair to say that this little American group kept in remarkably close touch with the enormous activity centered in Central Europe that

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506 BIOGRAPHICAL MEMOIRS was to leac! to the new quantum mechanics, and it contrib- uted at least two papers of real significance, one of which was Van's paper of 1924 on the correspondence principle for ab- sorption. This paper comes tantalizingly close to the kind of considerations that led to Heisenberg's matrix mechanics; it was one of the few papers to attack the intensity question that was the key failure of oIc! quantum theory. Van maintained close contact with European physics, and was fortunate enough to accompany his parents to Europe in 1923; during the trip he made time to visit Bohr and hack extended dis- cussions with Kramers in Holland. The University of Minnesota invited both Van ant! Greg- ory Breit to come as assistant professors in 1923. This was a unique opportunity. Only graduate teaching was requirecl, and he would have someone to talk with, because Breit's in- terests were very close to Van's, so he left the annual instruc- torship available to him at Harvard with no apparent reluc- tance. (Slater got the only permanent faculty job!) He was at Minnesota for five years, rising to associate professor in 1926 and full professor in 1927. On Tune 10, 1927, he married Abigail Pearson of Minneapolis. Of his courtship he re- marked that they both loved dancing and that her ignorance of his work assured him that she would never interfere in it. He jokocl later that he made up his mine! when, at a dance, she introducer! him as the professor of chemistry. His first book was published as a Bulletin of the National Research Council. At that time NRC committees were occa- sionally former! with the express purpose of informing American scientists about important developments, and this book was a report of the Committee on Optical Spectra, with Paul Foote as chairman. It was well received, but by the time it was issued in early 1926 much of it had been supersecled by the enormous explosion of results from the new quantum mechanics. The exercise, however, was of considerable value

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JOHN HASBROUCK VAN VLECK 507 to the author; his remarkably clear writing style had been formed, with the acknowledger! help of his father, and his very physical unclerstanding of classical dynamics and of the workings of the correspondence principle, which were to serve him well in his later career, hac! been developed. Van learned with great excitement of the new quantum mechanics through correspondence and the early published papers of Heisenberg on the matrix mechanics, which re- mainec! for a number of years his preferred form (in this, as in many other things, his style was unique). He sent in his first paper using it in early 1926, showing that the classical symmetry factor i/3 in the magnetic susceptibility is restored in the new theory. Nature asked him to shorten the piece, which slowed him down to what he called a "quadruple tie" in publication. He sailed for a visit to Copenhagen that sum- mer and completed another paper on the boat calculating mean values of inverse powers of r by matrix mechanics- only to learn that he had been beaten by practitioners of Schrodinger's wave mechanics. Nevertheless he wrote no less than four papers that year on the new mechanics, and for several years he continued to write papers discussing its na- ture and interpretation (such as tied. The little note in Nature fI0] was to set the theme for much of the rest of his career: the use of the new quantum mechanics to elucidate electromagnetic properties of matter. This had been an interest of his since an early seminar on the Weiss theory of ferromagnetism, and it was implicit in his correspondence principle paper; but from now on his inter- est led to a stream of fundamental papers, and it became clear that he hacI chosen this as his particular portion of the great work of verifying and using the new quantum theory. Bohr remarked, with characteristic insight, that while the spectroscopic successes of the quantum theory were more spectacular, the macroscopic ones such as Van worked on

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508 BIOGRAPHICAL MEMOIRS were in some ways "more satisfying ant! more fundamental." The most funclamental immediate results were his demon stration of the general formula (which he always carefully called "Langevin-Debye") for the susceptibility (papers Ll0], ~ ~ i], ~ ~ 5] in the accompanying bibliography) and the detailed application to O2 and NO FI21. But at this time, he had al- ready begun the work on molecular ant! other spectra in the new mechanics that was a second major theme in his life with a paper with Hill on rotational distortion tI61. He was asked by the chemists to review the new quantum mechanics Ll7], and in general was an important teacher and proselytizer of the new knowledge in the American context. His worldwide reputation was assured by the series of remarkable experi- mental verifications of his results on O2 and NO in Leyclen, MIT, ant! Zurich. WISCONSIN ( 1928 - 34) AND PREWAR HARVARD: MAGNETISM, MOLECULES, CRYSTAL FIELDS, AND THE ORIGIN OF MAGNETIC RELAXATION Although Minnesota was, as he later said, very congenial, with Breit as a coworker, Tate and other experimentalists encouraging him, and a number of bright auditors interested in his lectures (fate himself, Bleakney, Brattain, and others), physics was more active at Wisconsin. Van accepted an over of a professorship at the University of Wisconsin in 192S, remaining there until 1934. This gave him the pleasure of overlapping for one year with his father and renewing several old associations. It was at Wisconsin that he conceived and finished his book, Theory of Electric and Magnetic Susceptibilities, although much of it was written on a European trip in the summer of 1930. His stay in Zurich was particularly produc- tive; arriving in vacation time, he worked until Pauli returned and, with characteristic rudeness, said: "_ don't republish my papers into a book!" In fact, the book, aside from being ar

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JOHN HASBROUCK VAN VLECK 509 guably the first book in the modern field of solid-state phys- ics, contained-as Van defensively remarked much new material aside from the contents of the several papers on Langevin-Debye, "Van Vleck paramagnetism" (the second- order contribution of what he called "high-frequency matrix elements"), and the magnetism of the rare earth and iron group ions in salts (with Miss Frank (231), which had already appeared. There were new discussions of the averaging pro- cess for obtaining the fields ~ ~ ~ - ~ . 1 ~ fit in materials, of Heisenberg's tneory ot terromagnet~sm, ot aspects of ctielectric local fields and of dielectric theory in general, of Landau diamagnetism and its relationship to the classical theory, and the like. It is marked perhaps even slightly marred, as a modern text for physicists poorly trained in classical mechanics by careful discussion of the ways in which quantum mechanics, the old quantum theory, and classical physics differ. It just missed a number of very important developments, notably Van's own crystal field theory work and Neel and Landau's concept of antiferromagnetism, but in one sense it is not dated in the slightest: All results quoted in the book are, to my knowledge, correct to this day, needing no revision, only expansion. It was an enormously influential book and set a standard and a style for American solid-state physics that greatly influenced its development during decades to come for the better. We have, incidentally, R. H. Fowler's suggestion that Van write for the Oxford University Press to thank for the book's ex- istence. During the same Guggenheim fellowship trip that took Van to Zurich in 1930, he was invited to be the only American at the Solvay Congress. In Holland, he spent a number of days talking and walking with his friend Kramers, who pointed out to him Bethe's recent work on group theory. This led to a lifelong interest in group theory, which he still taught in inimitable style and from Wigner in the original Ger

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510 BIOGRAPHICAL MEMOIRS man-when ~ was at Harvard in 1948. It also led to a series of applications that Van seemed to fee} were among his best work: to the spectroscopy and susceptibilities of magnetic ions in solids (papers t25], t36], t43l, t45l, t53], L54], t60], t611; and papers by his students M. H. Hebb, R. SchIapp, and W. Penney, later Baron Penney, on most of which his name, characteristically, (lid not appear). In these papers he intro- duced the "crystal fielct" concept in which a magnetic ion is envisaged as behaving more or less like a free ion perturbed by the anisotropic potential of the surrounding ions and at- oms. The orbital angular momentum in most iron group ions in solicls is "quenched" (a typical Van concept) by such fields, because of the weakness of spin-orbit coupling relative to the crystal field splittings, while rare earth ions retain free ion character but responc! to the local symmetry by the appro- priate splittings of the energy levels. This concept correlates enormous masses of spectroscopic, magnetic, and even chem- ical data on these compounds (the chemical energetics were clevelopec! by Penney anct by Orge} and BalIhausen, much later). It provides an absolutely essential starting point for the understanding of all the technically important insulating magnetic materials, such as ferrites, garnets, ruby, and the like. Van initiated both of the main branches of the theory of crystal fielcis, the naive electrostatic version anct the "ligand field" theory (now more generally accepted) in which the em- phasis is on semicovalent bonding to the neighboring "li- gand" ions or groups; ant] with his characteristic flexibility he demonstrated (paper t434) that both led to essentially the same experimental results. In the chemistry and spectros- copy of these ions, Van's (or SchIapp and Penney's) name for the field strength parameter, "Dq," is still used. Of the crystal field theory it has been said by Moffitt ant! BalIhausen (per- haps a bit extravagantly, but Van likoct to quote this state- ment): "It will be a long time before a method is developed to surpass fit] in simplicity, elegance and power."

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JOHN HASBROUCK VAN VLECK 531 L43] Valence strength and the magnetism of complex salts. }. Chem. Phys., 3:807-13. 1936 [44] Nonorthogonality and ferromagnetism. Phys. Rev., 49:232 40. 1937 L45] The puzzle of rare-earth spectra in solids. }. Phys. Chem., 41 :67-80. L461 With R. L. Joseph. The influence of dipole-dipole coupling on the specific heat and susceptibility of a paramagnetic salt. J. Chem. Phys., 5:320-37; errata 32~1960~:1573. t471 On the role of dipole-dipole coupling in dielectric media. J. Chem. Phys., 5:556-68. t481 Revised calculation of the translational fluctuation effect in gaseous dielectrics. l. Chem. Phys., 5:991. t49] On the anisotropy of cubic ferromagnetic crystals. Phys. Rev., 52: 1178-98. 1938 L52] L501 On the adiabatic demagnetization of cesium titanium alum. J. Chem. Phys., 6:81-86. L511 Note on the second or Gaussian approximation in the Hei- senberg theory of ferromagnetism when S > /. l. Chem. Phys., 6:105-6. On the isotope corrections in molecular spectra. }. Chem. Phys., 4:327-38. 1939 F531 On the magnetic behavior chrome alum. }. Chem. Phys., 7:61-71. Of vanadium, titanium and t541 The Jahn-Teller effect and crystalline stark splitting for clus- ters of the form XY6. }. Chem. Phys., 7:72-84. With T. Bardeen. Expressions for the current in the Bloch approximation of "tight binding" for metallic electrons. Proc. Natl. Acad. Sci. USA, 25:82-86. t561 With G. W. King. Dipole-dipole resonance forces. Phys. Rev., 55:1165-72. F57] With G. W. King. Relative intensities of singlet-singlet and singlet-triplet transitions. Phys. Rev., 56:464 - 65.

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532 BIOGRAPHICAL MEMOIRS On the theory of the forward scattering of neutrons by par- amagnetic media. Phys. Rev., 55:924-30. 1940 F59] Paramagnetic relaxation times for titanium and chrome alum. Phys. Rev., 57:426-47, 1052. L60] Note on the Zeeman effect of chrome alum. i. Chem. Phys., 8:787-89. F61] With R. Finkelstein. On the energy levels of chrome alum. }. Chem. Phys., 8:790-97. F621 Electronic conduction and the equilibrium of lattice oscil- lators. Rev. Univ. Nac. Tucuman, Ser. A, 1:81-86. 1941 F631 On the theory of antiferromagnetism. J. Chem. Phys.,9:85- 90. L641 The influence of dipole-dipole coupling on the dielectric constants of liquids and solids. Ann. N.Y. Acad. Sci.,40:293- 313. L65] Note on Liouville's theorem and the Heisenberg uncertainty principle. Philos. Sci., 8:275-79. t661 Paramagnetic relaxation and the equilibrium of lattice oscil- lators. Phys. Rev., 59:724-29. F671 Calculation of energy exchange between lattice oscillators. Phys. Rev., 59:730-36. L681 Nuclear physics and inter-atomic arrangement. Univ. Pa. Bi- centennial Conf. :51- 68. 1945 L691 A survey of the theory of ferromagnetism. Rev. Mod. Phys., 17:27-47. L701 With V. F. Weisskopf. On the shape of collision-broadened lines. Rev. Mod. Phys., 17:227-36. 1946 t711 With B. P. Dailey, R. L. Kyhl, M. W. P. Strandberg, and E. B. Wilson, in The hyperfine structure of the microwave spec- trum of ammonia and the existence of a quadrupole mo- ment in N'4. Phys. Rev., 70:984.

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JOHN HASBROUCK VAN VLECK 533 F721 With D. Middleton. A theoretical comparison of the visual, aural and meter reception of pulsed signals in the presence of noise. J. Appl. Phys., 17 :940-71. 1947 F73] With F. Bloch and M. Hamermesh. Theory of radar reflec- tion from wires or thin metallic strips. ]. Appl. Phys., 18:274-94. F74] The absorption of microwaves by oxygen. Phys. Rev., 71 :413-24. The absorption of microwaves by uncondensed water vapor. Phys. Rev., 71:425-33. L76] With C. T. Gorter. The role of exchange interaction in par- amagnetic absorption. Phys. Rev., 72: 1128-29. L77] Quelques aspects de la theorie du magnetisme. Ann. Inst. Henri Poincare, 10: 57-187. 1948 L781 With R. S. Henderson. Coupling of electron spins in rotating polyatomic molecules. Phys. Rev., 74: 106 -7. t79] The dipolar broadening of magnetic resonance lines in crys- tals. Phys. Rev., 74:1168-83. 1949 L801 With L. H. Aller and C. W. Ufford. Multiplet intensities for the nebular lines 4S-2D of O. Astrophys. I., 109:42-52. F81 ~ The present status of the theory of ferromagnetism. Physica, 15: 197-206. F82] With Henry Margenau. Collision theories of pressure broad- ening of spectral lines. Phys. Rev., 76: 1211-14. 1950 L831 Concerning the theory of ferromagnetic resonance absorp- tion. Phys. Rev., 78:266-74. L841 With T. S. Kuhn. A simplified method of computing the cohesive energies of monovalent metals. Phys. Rev.,79:382- 88. t851 Landmarks in the theory of magnetism. Am. i. Phys., 13:495 -509.

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534 BIOGRAPHICAL MEMOIRS 1951 L861 Recent developments in the theory of antiferromagnetism. Phys, 12: 262-74. Ferromagnetic resonance. Physica, 17: 234-52. L871 L881 With I. Ollom. On the splitting of the ground state of Ni+ + in NiSiF~6H JO. Physica, 17:205 -8. F891 The coupling of angular momentum vectors in molecules. Rev. Mod. Phys., 23:213-27. 1952 L90] The significance of the results of microwave spectroscopy to the theory of magnetism. Ann. N.Y. Acad. Sci., 55:928-42. 1953 L91] Models of exchange coupling in ferromagnetic media. Rev. Mod. Phys., 25:220-27. L921 Two barrier phenomena. (Retiring address as president of the American Physical Society.) Phys. Today, 6:5-11. L93] With A. Abragam. Theory of the microwave Zeeman effect in atomic oxygen. Phys. Rev., 92:1448-55. 1954 L94] With G. R. Gunther-Mohr and C. H. Townes. Hyperfine structure in the spectrum of Ni4H3, II. Theoretical discus- sion. Phys. Rev., 94: 1191-1203. L951 With K. Kambe. Improved theory of the Zeeman effect of atomic oxygen. Phys. Rev., 96:66-71. L96] The cohesive energies of alkali metals. Proc. Int. Conf. Theor. Phys., Kyoto and Tokyo, pp. 640-49. 1955 L971 The role of Boltzmann factors in the impact model. Proc. Conf. Broadening of Spectral Lines. Pittsburgh: University of Pittsburgh. 1956 t981 Fundamental theory of ferro- and ferri-magnetism. Proc. IRE, 44:1248-58. t99] The theory of ferromagnetic anisotropy. AIEE Special Pub- lication T-91, Conference on Magnetism and Magnetic Ma- terials, October 16 -18.

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JOHN HASBROUCK VAN VLECK 535 [100] Blurred borders of physics and engineering. J. Eng. Educ., 46:366-73. 1957 t1011 Dangerous gulfs: Some reflections on the social implications of computing machines. In: The Computing Laboratory in the University, ed. Preston C. Hammer, pp. 223-32. Madison: The University of Wisconsin Press. F1021 With H. Meyer and Mary C. AI. O'Brien. The magnetic sus- ceptibility of oxygen in a clathrate compound, II. Proc. R. Soc. London, Ser. A, 243:414-21. 1031 Magnetic properties of metals. Nuovo Cimento, Suppl., 6:857-86. 1041 Line-breadths and the theory of magnetism. Nuovo Ci- mento, Suppl., 6:993-1014. F1051 The concept of temperature in magnetism. Nuovo Cimento, Suppl., 6: 1081-1100. 1958 1061 With }. Van Kranendonk. Spin waves. Rev. Mod. Phys., 30: 1-23. L107] The physical meaning of adiabatic magnetic susceptibilities. Z. Phys. Chem., 16:358-67. t1081 The magnetic behaviour of regular and inverted crystalline energy levels. Faraday Discuss. Chem. Soc., 26:96-102. 1959 L1091 Some recent progress in the theory of magnetism for non- migratory models. i. Phys., 20:124-35. F1101 Fundamental questions in magnetism. In: Magnetic Properties of Metals and Alloys, pp. 1-17. Metals Park, Ohio: American Society for Metals. 1960 F1111 The puzzle of spin-lattice relaxation at low temperatures. In: Quantum Electronics, a Symposium, ed. C. H. Townes, pp. 392- 409. New York; Columbia University Press. ~112] With C. Kittel. Theory of the temperature dependence of the magnetoelastic constants of cubic crystals. Phys. Rev., 118:1231-32.

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536 BIOGRAPHICAL MEMOIRS [113] With W. P. Wolf. Magnetism of europium garnet. Phys. Rev., 118: 1490-92. With R. M. Bozorth. Magnetic susceptibility of metallic eu- ropium. Phys. Rev., 118: 1493 -98. Frontiers of physical science in the Netherlands and the United States. Inaugural address as Lorentz Professor at the University of Leiden, March 4. Leiden: Leiden University Press. t1161 Note on the gyromagnetic ratio of Co++ and on the ~ahn- Teller effect in Fe+ +. Physica, 26:544-52. 1961 L1171 Relaxation mechanisms in nuclear magnetic resonance. Ned. Tijdschr. Natuurk., 27: 1-21. F1181 With I. A. White. Sign of Knight shift in samarium inter- metallic compounds. Phys. Rev. Lett., 6:412-13. L1191 Primitive theory of ferrimagnetic resonance frequencies in rare-earth iron garnets. Phys. Rev., 123:58-62. L120] Theory of the magnetic susceptibility of the nitric oxide clathrate. }. Phys. Chem. Solids, 20:241-54. L1211 With B. T. Matthias and R. M. Bozorth. Ferromagnetic in- teraction in EuO. Phys. Rev. Lett., 7:160-61. F122] Recent developments in spin-lattice relaxation. In: Advances in Quantum Electronics, ed. I. R. Singer, pp. 388 - 98. New York: Columbia University Press. 1962 F1231 Exchange fields in rare earth iron garnets. J. Phys. Soc. Tpn., Suppl. B-I, 17:352-57. (Also in: Proc. Int. Conf. Magn. Crys- tallogr. 1961, vol. I.) 1 24] The so-called age of science. In: Cherwell-Simon Memorial Lec- tures, 1961-62, pp. 25-50. Edinburgh: Oliver and Boyd. L125] Note on the interactions between the spins of magnetic ions or nuclei in metals. Rev. Mod. Phys., 34:681-86. F1261 Note on the use of the Dirac vector model in magnetic ma- terials. Rev. Univ. Nac. Tucuman, Ser. A, 14:189-96. F1271 The magnetism of some rare-earth compounds. In: Physical Sciences: Some Recent Advances in France and the United States, ed. H. P. Kallmann, S. A. Korff, and S. G. Roth, pp. 113- 28. New York: New York University Press.

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JOHN HASBROUCK VAN VLECK 1963 537 L1281 With R. Orbach. Ferrimagnetic resonance of dilute rare- earth doped iron garnets. Phys. Rev. Lett., 11 :65-67. L129] The theory of paramagnetic relaxation. In: Magnetic and Electric Resonance and Relaxation, Proceedings of the 11th Colloque Ampere, Eindhoven 1962, ed. J. Smidt, pp. 1-13. Amsterdam: North-Holland Publishing Co. L130] With W. H. Brumage and C. C. Lin. Magnetic susceptibility and crystalline field levels of ytterbium gallium garnet. Phys. Rev., 132:608-10. L1311 With R. C. LeCraw, W. G. Nilsen, and i. P. Remeika. Ferrom- agnetic relaxation in europium iron garnet. Phys. Rev. Lett., 11 :490-93. 1964 F1321 Ferrimagnetic resonance of rare-earth-doped iron garnets. Ferromagnetic resonance and relaxation. i. Appl. Phys., 35:882-88. L133] American physics comes of age (Michelson Prize Address). Phys. Today ~ June) :21-26. F1341 Theory of the relaxation of rare-earth iron garnets. In: Pro- ceedings, Magnetism Conference, Nottingham, pp. 401-3. 1966 F1351 With D. L. Huber. The role of Boltzmann factors in line shape. Rev. Mod. Phys., 38:187-204. 1361 With David Middleton. The spectrum of clipped noise. Proc. IEEE, 54: 2 - 19. F1371 The magnetic history of the rare earths. In: Proceedings of the Fourth Rare Earth Conference, Phoenix, April 1964, pp. 3-17. New York: Gordon and Breach. F1381 With M. M. Schieber and C. C. Lin. The magnetic behavior of thulium garnets in a cubic field. }. Phys. Chem. Solids, 27: 1041-45. L1391 Note on the crystal field parameters of rare earth garnets. t. Phys. Chem. Solids, 27:1047-51. F140] The molecular field model of exchange coupling in rare earth materials. In: Progress in the Science and Technology of the Rare Earths, vol. 2, pp. 1-22. New York: Pergamon Press.

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538 BIOGRAPHICAL MEMOIRS t1411 Some elementary thoughts on the Slater intra-atomic ex- change model for ferromagnetism. In: Quantum Theory of Atoms, Molecules, and the Solid State, pp. 475-84. New York: Academic Press. 1967 L1421 The evolution of crystal field parameters for rare earth salts. In: Interaction of Radiation with Solids, pp. 649-62, New York: Plenum Press. L1431 Thirty years of microwave spectroscopy (Fourth Annual A1- pheus W. Smith Lecture). Columbus: Ohio State University. 1441 Non-mathematical theoretical physics. Sci. Light (Tokyo), 16:43-49. 1968 [145] Magnetic case history of the Eu3 - ion. J. Appl. Phys., 39:365-72. do. ~ 1461 The widening world of magnetism. Phys. Bull., 19: 167-75. L1471 With N. L. Huang. Strong orbital anisotropy in the exchange interaction in Fe3+Eu:GaG. Solid State Commun., 6:557-59. 148] With Sidney Coleman. Origin of "hidden momentum forces" on magnets. Phys. Rev., 1 7 1 (51: 1 370-75. 1491 My Swiss visits of 1906, 1926, and 1930. Helv. Phys. Acta, 41:1234-35. 1969 F1501 With N. L. Huang. Isotropic coupling caused by anisotropic exchange in Eu=?O3. In: Polarization, Matiere et Rayonnement, volume jubliaire en lthonneur d'Alfred Kastler, pp. 507-21. Paris: Presses Universitaires de France. t1511 With N. L. Huang. Note on the Dirac electron and hidden momentum forces. Phys. Lett., 28A:768-69. L1521 With N. L. Huang. Effect of the anisotropic exchange and the crystalline field on the magnetic susceptibility of Eu~O~. J. Appl. Phys., 40: 1144 -46. L1531 With N. L. Huang. Magnetic susceptibility of nitric oxide molecules absorbed on silica gel. }. Chem. Phys., 50:2932- 35.

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JOHN HASBROUCK VAN VLECK 539 1970 [154] A third of a century of paramagnetic relaxation and reso- nance. In: Magnetic Resonance (a symposium held in Mel- bourne, 1969), pp. 1-10. New York: Plenum Press. L155] Spin, the great indicator of valence behavior. Pure Appl. Chem., 24:235-55. L1561 Group theory for permutation degeneracy in four electrons, and the Pauli exclusion principle. Bull. Polytech. Inst. Jassy, Rumania, 16~20~:3-4. L1571 A lyrical account of magnetism, prelude to a new journal. Int. }. Magn., 1:1-9. 1971 F1581 Reminiscences of the first decade of quantum mechanics. Int. I. Quantum Chem., 5:3-20. 1972 L1591 With R. M. Bozorth and A. E. Clark. Magnetic crystal ani- sotropies of holmium-erbium alloys. Int. I. Magn., 2: 19-31. L1601 On the theory of the dielectric constant of dilute solutions of polar molecules in non-polar solvents. Mol. Phys.,24:341- 48. L1611 Travels with Dirac in the Rockies. In: Aspects of Quantum Theory, ed. A. Salam and E. P. Wigner, pp. 7-16. Cambridge: Cambridge University Press. 1973 F1621 Central fields in two vis-a-vis three dimensions: An historical divertissement. In: Wave Mechanics, pp. 26-37. London: Butterworths. F1631 X = C/(T + 1~), The most overworked formula in the history of paramagnetism. Physica, 69: 177-92. 1974 F1641 With M. E. Foglio. Theory of the magnetic anisotropy and nuclear magnetic resonance of europium iron garnet. Proc. R. Soc. London, Ser. A, 336:115-40. 1651 Koninklijke Nederlandse Akademie van Wetenschappen. Bijzondere Bijeenkomst der Afdeling Natuurkunde op za

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540 BIOGRAPHICAL MEMOIRS terdag 28 September 1974, des namiddags te 3.30 our, voor de plechtige uitreiking van de Lorentz-medaille aan Prof. Dr. }. H. Van Vleck. Cambridge: Harvard University, 13 pp. 1975 L1661 With M. E. Foglio and R. F. Sekerka. Theory of the width of the ferromagnetic resonance line of europium iron garnet. Proc. R. Soc. London, Ser. A, 344:21-50. 1977 F1671 With D. L. Huber. Absorption, emission, and linebreadths: A semihistorical perspective. Rev. Mod. Phys., 49:939-49. 1978 L1681 Quantum mechanics: The key to understanding magnetism. Science, 201: 113-20. 1980 t169] Reminiscences of my scientific rapport with R. S. Mulliken. i. Phys. Chem., 84:2091-95. BOOKS 1926 Quantum Principles and Line Spectra. Washington, D.C. search Council Bull. 54. 316 pp. 1932 : National Re The Theory of Electric and Magnetic Susceptibilities. Oxford: Oxford University Press. 384 pp.

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