title: Insulating Nanomagnets Driven by Spin Torque.
abstract: Magnetic insulators, such as yttrium iron garnet (Y3Fe5O12), are ideal materials for ultralow power spintronics applications due to their low energy dissipation and efficient spin current generation and transmission. Recently, it has been realized that spin dynamics can be driven very effectively in micrometer-sized Y3Fe5O12/Pt heterostructures by spin-Hall effects. We demonstrate here the excitation and detection of spin dynamics in Y3Fe5O12/Pt nanowires by spin-torque ferromagnetic resonance. The nanowires defined via electron-beam lithography are fabricated by conventional room temperature sputtering deposition on Gd3Ga5O12substrates and lift-off. We observe field-like and antidamping-like torques acting on the magnetization precession, which are due to simultaneous excitation by Oersted fields and spin-Hall torques. The Y3Fe5O12/Pt nanowires are thoroughly examined over a wide frequency and power range. We observe a large change in the resonance field at high microwave powers, which is attributed to a decreasing effective magnetization due to microwave absorption. These heating effects are much more pronounced in the investigated nanostructures than in comparable micron-sized samples. By comparing different nanowire widths, the importance of geometrical confinements for magnetization dynamics becomes evident: quantized spin-wave modes across the width of the wires are observed in the spectra. Our results are the first stepping stones toward the realization of integrated magnonic logic devices based on insulators, where nanomagnets play an essential role.
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Matthias B
authors.initials: MB
authors.lastname: Jungfleisch
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Junjia
authors.initials: J
authors.lastname: Ding
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.|Department of Physics, Oakland University , Rochester, Michigan 48309, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.|State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
authors.forename: Wanjun
authors.initials: W
authors.lastname: Jiang
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: John E
authors.initials: JE
authors.lastname: Pearson
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Valentine
authors.initials: V
authors.lastname: Novosad
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Axel
authors.initials: A
authors.lastname: Hoffmann
mesh_terms: D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D059346:Magnets / Q000737:chemistry*; D008872:Microwaves; D053770:Nanowires / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D010984:Platinum / Q000737:chemistry; D019415:Torque; D015019:Yttrium / Q000737:chemistry*
chemical_list: D010087:Oxides; D010984:Platinum; D015019:Yttrium; D007501:Iron
keywords: Spin-torque ferromagnetic resonance; magnetization dynamics; platinum; spin-Hall effect; spin-transfer torque; yttrium iron garnet