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 studied at

Leiden University Leiden University (abbreviated as ''LEI''; ) is a Public university, public research university in Leiden, Netherlands. Established in 1575 by William the Silent, William, Prince of Orange as a Protestantism, Protestant institution, it holds the d ...

under the guidance of

Hendrik Antoon Lorentz Hendrik Antoon Lorentz ( ; ; 18 July 1853 – 4 February 1928) was a Dutch theoretical physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for their discovery and theoretical explanation of the Zeeman effect. He derived ...

, obtaining her doctorate in 1919. Her thesis explained why

magnetism Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, ...

is an essentially quantum mechanical effect, a result now referred to as the Bohr–Van Leeuwen theorem. (

Niels Bohr Niels Henrik David Bohr (, ; ; 7 October 1885 – 18 November 1962) was a Danish theoretical physicist who made foundational contributions to understanding atomic structure and old quantum theory, quantum theory, for which he received the No ...

had arrived at the same conclusion a few years earlier.) She continued to investigate magnetic materials at the "Technische Hogeschool Delft" (now called the

Delft University of Technology The Delft University of Technology (TU Delft; ) is the oldest and largest Dutch public university, public Institute of technology, technical university, located in Delft, Netherlands. It specializes in engineering, technology, computing, design, a ...

), first as "assistant" between September 1920 and April 1947, and then she was promoted to " lector in de theoretische en toegepaste natuurkunde" (reader in theoretical and applied physics). Hendrika van Leeuwen was the sister-in-law of Gunnar Nordström, known as the "Einstein of Finland", who studied in Leiden with

Paul Ehrenfest Paul Ehrenfest (; 18 January 1880 – 25 September 1933) was an Austrian Theoretical physics, theoretical physicist who made major contributions to statistical mechanics and its relation to quantum physics, quantum mechanics, including the theory ...

, 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. Van Leeuwen was present at 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. The English translation of the Dutch text reads: ''For us, his pupils, Lorentz was not only the great scientist, but also an example to follow as a friendly, upbeat person with a great sense of duty, admirable simplicity and warm interest for all around him. Many a great physicist enjoyed being one of Lorentz's students for a shorter or longer period of time. There is no better way to honor our great teacher, than to attempt to continue our own work with all our strengths, enthusiasm and care.''

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