Microwave Absorption by 1D, 2D and 3D Random Magnets
Abstract
The goal of this project is to investigate the microwave absorption of 1D (wires), 2D (foils) and 3D (particles and bulk materials) ceramic and nanometallic systems with properties of random magnets. Ferromagnets with long-range order possess propagating spin waves. Excitation of spin waves contributes to their microwave properties. In random magnets, spin waves are believed to be localized and their contribution to microwave absorption remains unclear. Despite its fundamental value, this problem was scarcely addressed in the past. Theoretical progress in this area has been recently achieved (under the support of an AFOSR grant) by the group of Prof. Chudnovsky at the City University of New York (Physical Review B-2021,2022). Our goal is to test theoretical predictions experimentally. Among the most interesting predictions is localization of magnetic excitations induced by the microwaves inside resonant Imry-Ma domains in amorphous ferromagnets. We will also test the predicted broadband absorption due to the broad distribution of resonances, and differences caused by the dimensionality, by working with systems composed of microscopic magnetic wires, foils and particles. The long-standing fundamental question about the nature of the short-range ordering in random magnets, freezing due to energy barriers vs a spin-glass transition, will be investigated with the help of dc and ac measurements of the temperature dependence of the magnetization. The planned research will capitalize on recent observations by the proposer’s group of the record (in excess of -60dB in the 10-GHz frequency range) microwave absorption by a random magnet composed of magnetic nanoparticles densely packed in a dielectric medium. The absorption scenarios suggested by theorists, such as localization of spin excitations in magnetically ordered nanoscale domains and dissipation of the microwave energy due the motion of domain walls, will be tested in experiments.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 20, 2023
- Source ID
- FA86552217049
Entities
People
- Javier Tejada Palacios
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Barcelona