Showing papers by "John B Ketterson published in 2021"

Ferromagnetic resonance in single vertices and 2D lattices macro-dipoles of elongated nanoelements: measurements and simulations.

Abstract: We report broadband ferromagnetic resonance measurements of the in-plane magnetic field response of three- and four-fold symmetric vertices formed by non-contacting permalloy nano-ellipses together with extended lattices constructed from them. Complementing the experimental data with simulations, we are able to show that, as far as the most intense FMR responses are concerned, the spectra of vertices and lattices can largely be interpreted in terms of a superposition of the underlying hysteretic responses of the individual ellipses, as elemental building blocks of the system. This property suggest that it is possible to understand the orientation of the individual magnetic dipole moments in a dipole network in terms of dynamic measurements alone, thereby offering a powerful tool to analyze the alignment statistics in frustrated systems that are exposed to various magnetic histories.

Amorphous to Crystal Phase Change Memory Effect with Two-Fold Bandgap Difference in Semiconducting K2Bi8Se13.

Abstract: Chalcogenide-based phase change memory (PCM) is a key enabling technology for optical data storage and electrical nonvolatile memory. Here, we report a new phase change chalcogenide consisting of a...

Magnetic Field Sensor Based on a Single Josephson Junction With a Multilayer Ferromagnet/Normal Metal Barrier

Abstract: We report experimental studies of quantum-matter heterostructures based on a ferromagnet/normal metal multilayer proximitized by Nb superconducting electrodes to form a novel Josephson weak-link device that is highly sensitive to magnetic fields. The device is a single Josephson junction containing Al/Ni or Al/Py (Py: Ni80Fe20) multilayer structures, which manifests quasi-sinusoidal critical current oscillations resembling the response of a dc Superconducting Quantum Interference Device (SQUID). Our analysis shows that the field sensitivity of this novel device, as measured by the magnetic field needed to form one period of the oscillations, is about twice that reported for recent micro- or nano-SQUIDs. We present an analysis of the temperature dependence of the period of the oscillations and the Josephson critical current, as well as the background current. We believe that our devices are promising candidates for a new generation of magnetic field nanosensors.

Ferromagnetic resonance modes in the exchange dominated limit in cylinders of finite length

Abstract: We analyze the magnetic mode structure of axially-magnetized, finite-length, nanoscopic cylinders in a regime where the exchange interaction dominates, along with simulations of the mode frequencies of the ferrimagnet yttrium iron garnet. For the bulk modes we find that the frequencies can be represented by an expression given by Herring and Kittel by using wavevector components obtained by fitting the mode patterns emerging from these simulations. In addition to the axial, radial, and azimuthal modes that are present in an infinite cylinder, we find localized "cap modes" that are "trapped" at the top and bottom cylinder faces by the inhomogeneous dipole field emerging from the ends. Semi-quantitative explanations are given for some of the modes in terms of a one-dimensional Schrodinger equation which is valid in the exchange dominant case. The assignment of the azimuthal mode number is carefully discussed and the frequency splitting of a few pairs of nearly degenerate modes is determined through the beat pattern emerging from them.