title: Negative dissipation gradients in hysteretic materials.
abstract: Measuring energy dissipation on the nanoscale is of great interest not only for nanomechanics but also to understand important energy transformation and loss mechanisms that determine the efficiency of energy of data storage devices. Fully understanding the magnetic dynamics and dissipation processes in nanomagnets is of major relevance for a number of basic and applied issues from magnetic recording to spin-based sensor devices to biomedical magnetic-based hyperthermia treatments. Here we present experimental evidence for a counter-intuitive monotonical reduction of energy dissipation as the interaction between two nanomagnets is enhanced. This behavior, which takes place when spins are parallel, can be understood in terms of hysteresis phenomena involved in the reorientation of these spins. The measured magnetic losses of about a few femtowatts are in agreement with quasi-static micromagnetic numerical simulations.
authors.affiliation: Instituto de Ciencia de Materiales de Madrid-CSIC, 28049 Madrid, Spain. aasenjo@icmm.csic.es.
authors.forename: Miriam
authors.initials: M
authors.lastname: Jaafar
authors.affiliation: Instituto de Ciencia de Materiales de Madrid-CSIC, 28049 Madrid, Spain. aasenjo@icmm.csic.es and Department of Physics, McGill University, Montreal, H3A 2T8, Canada.
authors.forename: Óscar
authors.identifier: http://orcid.org/0000-0002-2112-4219
authors.initials: Ó
authors.lastname: Iglesias-Freire
authors.affiliation: Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: García-Mochales
authors.affiliation: Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián, Spain. juanjo.saenz@dipc.org and IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain.
authors.forename: Juan José
authors.identifier: http://orcid.org/0000-0002-1411-5648
authors.initials: JJ
authors.lastname: Sáenz
authors.affiliation: Instituto de Ciencia de Materiales de Madrid-CSIC, 28049 Madrid, Spain. aasenjo@icmm.csic.es.
authors.forename: Agustina
authors.identifier: http://orcid.org/0000-0001-6524-9702
authors.initials: A
authors.lastname: Asenjo