Interdisciplinary Team Reports Extremely High Resonant Frequency in Cobalt-Palladium Multilayers

Finding Has Significant Technological Applications

Scientists at the University of Minnesota have reported direct observation of magnon-phonon coupling in time and frequency domains under femtosecond laser excitation. Based on their observations, the team have also proposed a theoretical model explaining the physical mechanism underlying this strain-spin interaction. The results of their work are reported in “High-frequency magnetoacoustic resonance through strain-spin coupling in perpendicular magnetic multilayers,” published in Science Advances. The work is significant for the impact it could have on applications in cloud storage, and spintronic devices.

The research was conducted by an interdisciplinary team of researchers working in close collaboration over the past three years. Dr. Delin Zhang and Distinguished McKnight University Professor of Electrical and Computer Engineering Jian-Ping Wang designed and synthesized the samples and carried out the magnetic measurements.

Dr. Zhang is excited about the potential impact of the team’s work: “I am very glad to complete this exciting piece of work together with our team, which has taken about three years starting from the CSPIN time. It is very exciting to know that spintronic materials prepared in our labs could be useful one day for the semiconductor industry ”.

Dr. Jie Zhang, Dr. Dustin Lattery, an alumnus of the Dept. of Mechanical Engineering, and Prof. Xiaojia Wang led the ultra fast magnetic dynamic measurement and characterization using an ultra fast laser setup. Dr. Tao Qu, an alumnus of the School of Physics and Astronomy, and Prof. Randall Victora carried out the theoretical calculations and predictions. The work has been supported by the CSPIN center, one of the SRC-DARPA STARnet centers.

Commenting on the interdisciplinary nature of the study, Prof. Xiaojia Wang says, “It is fun to be part of this interdisciplinary team. I am happy that the ultra fast laser-based metrology plays a critical role in this work. It can capture the extremely high resonance frequency between the spin and acoustic strain, which could not be done with other approaches”

SIGNIFICANCE OF THE STUDY

Most studies on magnon-phonon coupling have been conducted on materials that are unsuitable for spintronic applications. And there have not been experimental demonstrations of either magnon-phonon coupling, or ultra high frequency magnetoacoustic resonance in materials with perpendicular magnetic anisotropy (PMA). The present research addresses this by using Cobalt-Palladium multilayers as these materials have high perpendicular magnetic anisotropy (PMA), and a relatively large magnetostriction coefficient. These characteristics make them potentially valuable for technological applications, and serve as an ideal platform for investigating the magnon-phonon coupling.

Coupling of Magnons and Phonons in Both Time and Frequency Domains upon Femtosecond Laser Excitation

The study authors have reported an extremely high frequency (EHF) magnetoacoustic resonance up to 60 GHz in the Cobalt-Palladium multilayer from the strong magnon-phonon coupling that resulted from excitation by femtosecond laser pulses. The present research holds twofold significance: it opens up a potential pathway to enabling an EHF magnetoacoustic resonance through the magnon-phonon coupling, and suggests the possibility of ultra high-speed strain-assisted magnetization switching in a technologically relevant magnetic system. Additionally, the team have developed a theoretical model that explains the physical mechanism of magnetoacoustic resonance that follows the strain-spin interaction within an energy viewpoint.

Study author Prof. Victora, drawing attention to the innovative nature of the work, says: “The theoretical work by my postdoctoral researcher Tao Qu provided a consistent and quantitative explanation of the experimentally observed data, lending credence to our predictions that the magneto-acoustical interaction can yield rapid switching of magnetization and thus very high data rate storage.”

Taking the results of their research to the realm of application, the demonstration offers an approach to meeting future technological needs of high speed and highly compact memory. The work is significant for the impact it could have on applications in cloud storage, advanced spin memory, logic, and other spintronic devices.

Learn more about Prof. Jian-Ping Wang’s research

Learn more about Prof. Randall Victora’s research

Learn more about Prof. Xiaojia Wang’s research