Hendrika Johanna van Leeuwen
Hendrika Johanna van Leeuwen (July 3, 1887 – February 26, 1974) was a Dutch physicist known for her early contributions to the theory of magnetism. She demonstrated that magnetism in matter can only be explained using quantum mechanics. She was one of the first women to study physics at a university level in the Netherlands.[1] CareerVan Leeuwen was born in 1887. Her parents enrolled her and her sister in the Hague boys' school when it began accepting female students in 1901, although it still required applying for a special ministerial permit. Her parents also allowed her to take the examination in Greek and Latin, a prerequisite for university studies.[1] She studied at Leiden University under the guidance of Hendrik Antoon Lorentz, beginning her doctoral work in 1914 and obtaining her doctorate in 1919. She was not Lorentz's first female doctoral student; three other women had earned their doctorates with him earlier.[1] Her thesis[2][3] explained why magnetism in solids is an fundamentally a quantum mechanical effect.[4] Her starting point was Lorentz's classical electron theory and his observation that classical free-moving electrons in a metal do not generate a net magnetic moment. She examined a range of other systems and concluded that any classical system in a magnetic field and in thermal equilibrium has no magnetic dipole moment. In other words, classical physics cannot produce any kind of magnetism.[1] Niels Bohr independently discovered the principle in his 1911 doctoral thesis, but his work was not widely known because it was written in Danish and he was not yet a prominent figure. The result became well known after Van Leeuwen published an article based on her doctoral thesis in 1921. In his 1932 book, John Van Vleck named the discovery "Miss van Leeuwen's theorem", highlighting her more comprehensive analysis compared to Bohr's. By 1977 the credit had shifted: In his Nobel lecture, Van Vleck emphasized Bohr's contribution, and van Leeuwen's name was relegated to a footnote.[1] The discovery is now usually referred to as the Bohr–Van Leeuwen theorem, acknowledging both contributions.[5] She continued to investigate magnetic materials at the "Technische Hogeschool Delft" (now called the Delft University of Technology). She was appointed as an assistant in September 1920, a role she held for nearly thirty years. In this position, she supervised laboratory courses in electrical engineering. Her teaching was appreciated by her students, but it left her with little time for research.[1][5] In April 1947, at the age of 59, she was promoted to "lector in de theoretische en toegepaste natuurkunde" (reader in theoretical and applied physics) which entitled her to teach her own courses.[6][7][5] This appointment was considered long overdue by her contemporaries, and came too late for her to build a career in research.[1] Personal lifeHendrika van Leeuwen was the sister-in-law of Gunnar Nordström, known as the "Einstein of Finland", who studied in Leiden with Paul Ehrenfest, the successor of Lorentz. Her sister Cornelia (Nel) also started a PhD in Leiden, under Willem Hendrik Keesom, but stopped when she married Nordström and moved with him to Helsinki.[7]  Van Leeuwen remained close with her doctoral advisor Lorentz until his death in 1928.[5] She attended the celebration of the golden anniversary of the doctorate of Lorentz, on 11 December 1925, and on that occasion reported on the role of Lorentz as scientist and teacher.[8] Selected works
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