I am delighted that the AGU Geomagnetism, Paleomagnetism, and Electromagnetism (GPE) section has chosen Suzanne McEnroe to receive the 2019 William Gilbert Award. In her career, Suzanne has carried out groundbreaking fundamental research on magnetic anomaly sources in the crust, with implications that reach broadly throughout the Earth and planetary sciences. Her interest has been particularly focused on the significant negative, remanence-dominated magnetic anomalies that occur in various locations. Her careful analyses showed in multiple cases that this remanence originated primarily in crystals of the hematite-ilmenite series, containing abundant fine-scale exsolution structures. Although a few earlier studies had also reached this conclusion, they had not been able to explain the combination of very high magnetic stability and high magnetic intensity. The key insight from Suzanne and her collaborators was that the exsolution microstructures do not merely affect the properties of the host minerals, but are themselves the source of the strong and stable remanence, through a previously unknown interfacial ordering mechanism termed lamellar magnetism.
Two principal factors have propelled her continuing studies of these remanence sources to the forefront of mineral magnetic research: first, her comprehensive approach to characterization (using scanning electron microscopy, transmission electron microscopy, magnetic microscopy, Mössbauer spectroscopy, low-temperature high-field magnetometry, and theoretical modeling), and second, her initiative in developing and coordinating collaborations involving talented specialists in each of these techniques. Two brilliant series of papers have comprehensively illuminated the phenomenon of lamellar magnetism in hematite-ilmenite nanocomposites, as well as the complex chemical and magnetic ordering in metastable homogeneous mineral phases over the same range of bulk compositions. These papers collectively represent one of the greatest achievements in mineral and rock magnetism over the past 2 decades.
I am honored to congratulate Suzanne McEnroe, our 2019 William Gilbert Award recipient, for her leadership in research that has transformed our understanding of mineral magnetism, paleomagnetic field records, and geomagnetic field anomalies.
—Michael J. Jackson, University of Minnesota, Twin Cities, Saint Paul
I am honored to receive the William Gilbert Award from the AGU GPE section for my work on magnetic anomalies and mineral magnetism. Working to understand the nature and sources of magnetization from unusual magnetic anomalies at the kilometer scale led to scientific breakthroughs in mineral magnetism at the atomic scale. The anomaly hunt started when I was a postdoc and picked up a discarded paper on oxide mineralogy and anomalies in the Adirondack Mountains by Balsley and Buddington, who noted that the source of the negative anomalies was elusive. Reading this classic paper changed my scientific direction. I went to the Adirondacks, collected samples, and concluded that these magnetic anomalies could not be interpreted using traditional magnetic mineralogy concepts.
Work on remanent anomalies and mineralogy continued in Sweden, Norway, and Australia. To account for the bulk magnetization found in rocks where the source was ilmenite-hematite, a study of the interactions at micro and atomic scales was required. This led to the theory of lamellar magnetism, which required a change in our thinking from a bulk (volume) magnetization to a surface magnetization at interfaces, as in ilmenite-hematite exsolutions. This interface magnetization could result in a large remanent magnetization due to the fine scale of exsolution lamellae (from micrometer to nanometer size), providing an abundant surface magnetization. The next aspect was finding the nature of the coercivity of these mineral intergrowths. Tackling these questions required scientific collaborators from disciplines in mineralogy, physics, chemistry, and crystallography. I have been extraordinarily fortunate to work with highly talented scientists. I am very grateful for access to the Institute for Rock Magnetism, for rock-magnetic measurements, and to the Bayerisches Geoinstitut in Germany for experimental work with Falko Langenhorst, Catherine McCammon, and Nobuyoshi Miyajima, and for my long-term collaborators Laurie Brown, Karl Fabian, Richard Harrison, and especially Peter Robinson. Peter was the giant and the cornerstone of all this research.
—Suzanne A. McEnroe, Institute of Geoscience and Petroleum, Norwegian University of Science and Technology, Trondheim, Norway