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Displaying 1 - 25 of 120

Challenges for Sub-PicoTesla Magnetic-Tunnel-Junction Sensors

October 12, 2021
Robert McMichael, Philip Pong, John Unguris, William F. Egelhoff Jr., A Edelstein, E Nowak, Sean R. Parkin
The extension of small, inexpensive, low-power magnetic sensors into the sub-picoTesla regime, which is currently dominated by fluxgates and SQUIDS, would be a paradigm shift for the field of magnetic sensors. The necessary elements for sub-picoTesla MTJ

Magnetic depth profiling Co/Cu multilayers to investigate magnetoresistance

October 12, 2021
John Unguris, D. Tulchinsky, Michael H. Kelley, Julie Borchers, Joseph Dura, Charles Majkrzak, S. Y. Hsu, R. Loloee, W. P. Pratt, J. Bass
The magnetic microstructure responsible for the metastable high resistance state of weakly coupled, as-prepared [Co(6nm)/Cu(6nm)]20 multilayers was analyzed using polarized neutron reflectivity and scanning electron microscopy with polarization analysis

Bubble magnetometry of nanoparticle heterogeneity and interaction

June 7, 2019
Andrew L. Balk, Ian J. Gilbert, R. Ivkov, John Unguris, Samuel Stavis
Bubbles have a rich history as transducers in particle-physics experiments. In a solid-state analogue, we use bubble domains in nanomagnetic films to measure magnetic nanoparticles. This technique can determine the magnetic orientation of a single

Electric-Field Induced Reversible Switching of the Magnetic Easy Axis in Co/BiFeO 3 on SrTiO 3

April 18, 2017
Tieren Gao, Xiaohang Zhang, William D. Ratcliff, Shingo Maruyama, Makoto Murakami, Anbusathaiah Varatharajan, Zahra Yamani, Peijie Chen, Ke Wang, Huairuo Zhang, Robert D. Shull, Leonid A. Bendersky, John Unguris, R. Ramesh, Ramamoorthy Ramesh, I. Takeuchi
We demonstrate reversible electric-field-induced switching of the magnetic state of the Co layer in Co/BiFeO3 (BFO) (001) thin film heterostructures fabricated on (001) SrTiO3 substrates. The angular dependence of the coercivity and the remanent

Spatially resolved ferroelectric domain-switching-controlled magnetism in Co 40 Fe 40 B 20 /Pb(Mg 1/3 Nb 2/3 ) 0.7 Ti 0.3 O 3 multiferroic heterostructure

December 27, 2016
Peisen Li, Yonggang Zhao, Sen Zhang, Aitian Chen, Dalai Li, Jing Ma, Yan Liu, Daniel T. Pierce, John Unguris, Hongguang Piao, Huiyun Zhang, Meihong Zhu, Xiaozhong Zhang, Xiufeng Han, Mengchun Pan, Ce-Wen Nan
Intrinsic spatial inhomogeneity or phase separation in cuprates and manganites etc., related to electronic and/or magnetic properties, has attracted much attention due to its significance in fundamental physics and applications. Here we use scanning Kerr

Magnetic microscopy and simulation of strain-mediated control of magnetization in Ni/PMN-PT nanostructures

October 17, 2016
Ian J. Gilbert, Andres C. Chavez, Daniel T. Pierce, John Unguris, Wei-Yang Sun, Cheng-Yen Liang, Gregory P. Carman
Strain-mediated thin film multiferroics comprising piezoelectric/ferromagnetic heterostructures enable the electrical manipulation of magnetization with much greater efficiency than other methods; however, the investigation of nanostructures fabricated

Nanoscale imaging of magnetization reversal driven by spin-orbit torque

September 23, 2016
Ian J. Gilbert, Andrew P. Chen, Daniel B. Gopman, Andrew L. Balk, Daniel T. Pierce, Mark D. Stiles, John Unguris
We use scanning electron microscopy with polarization analysis (SEMPA) to image deterministic, spin-orbit torque driven magnetization reversal of in-plane magnetized CoFeB rectangles in zero applied magnetic field. The spin-orbit torque is generated by

Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals

April 25, 2016
Barry Farmer, Vinayak Bhat, Andrew L. Balk, Eric Teipel, Nathan Smith, John Unguris, D.J. Keavney, Todd Hastings, L .E. De Long
Quasicrystals are rarely found in nature and are difficult to grow in the laboratory, but exhibit unique physical properties resulting from their signature long-range structural order without periodic translational symmetry. Magnetic interactions in

Realization of Ground-State Artificial Skyrmion Lattices at Room Temperature

October 8, 2015
Dustin A. Gilbert, Brian B. Maranville, Andy L. Balk, Brian J. Kirby, Peter Fischer, Daniel T. Pierce, John Unguris, Julie A. Borchers, Kai Liu
The topological nature of magnetic skyrmions deriving from broken symmetries leads to extraordinary static and dynamic properties that provide new insight in fundamental problems of magnetism and exciting potentials for exploitation in novel magnetic

Quantitative magnetometry of ferromagnetic nanorods by microfluidic analytical magnetophoresis

September 3, 2015
Andrew L. Balk, Lamar O. Mair, Feng Guo, Carlos M. Hangarter, Pramod Mathai, Robert D. McMichael, Samuel M. Stavis, John Unguris
We introduce an implementation of magnetophoresis to measure the absolute magnetization of ferromagnetic nanorods dispersed in fluids, by analyzing the velocity of single nanorods under an applied magnetic field gradient. A microfluidic guideway prevents

Probing electric field control of magnetism using ferromagnetic resonance

January 29, 2015
Ziyao Zhou, Morgan Trassin, Ya Gao, Yuan Gao, Diana Qiu, Khalid Ashraf, Tianxiang Nan, Xi Yang, Samuel R. Bowden, Daniel T. Pierce, Mark D. Stiles, John Unguris, Ming Liu, Brandon Howe, Gail Brown, Sayeef Salahuddin, Ramamoorthy Ramesh, Nian Sun
A question of fundamental importance in multiferroic materials, such as BiFeO3, is whether the canted moment arising from the Dzyalozhinski-Moriya coupling is switchable with the application of an electric field. Since this canted moment is weak, directly

Interfacial Coupling in Multiferroic/Ferromagnet Heterostructures

April 30, 2013
M. Trassin, J. D. Clarkson, Samuel R. Bowden, j. Liu, J. T. Heron, R. J. Paull, Elke Arenholz, Daniel T. Pierce, John Unguris
We report local probe investigations of the magnetic interaction between BiFeO3 films and a ferromagnetic Co0.9Fe0.1 layer. Within the constraints of intralayer exchange coupling in the Co0.9Fe0.1, the multiferroic imprint in the ferromagnet results in a

Optimization of Spin-triplet Supercurrent in Ferromagnetic Josephson Junctions

March 20, 2012
Benjamin James McMorran, Theresa Ginley, Julie Borchers, Brian Kirby, Brian B. Maranville, John Unguris
In the past year, several groups have observed evidence for long-range spin-triplet, supercurrent in Josephson junctions containing ferromagnetic (F) materials. In our work, the spin-triplet pair correlations are created by non-collinear magnetizations

Formation and structure of 360 and 540 degree domain walls in thin magnetic stripes

February 10, 2012
Youngman Jang, Samuel R. Bowden, Mark Mascaro, John Unguris, Caroline Ross
360˚, 540˚ and other complex transverse domain walls have been created in narrow Co wires connected to injection pads by cycling a magnetic field perpendicular to the wire length. The composite walls, formed by impingement of 180˚ transverse walls of

Magnetization textures in NiPd nanostructures

September 15, 2011
Jean-Yves Chauleau, Benjamin James McMorran, R. Belkhou, Nicolas Bergeard, Tevfik Mente?, Miguel Angel Nino, Andrea Locatelli, John Unguris, Stanislas Rohart, Jacques Miltat, Andre Thiaville
We have observed peculiar magnetization textures in Ni80Pd20 nanostructures, by three different imaging techniques (MFM, XMCD-PEEM and SEMPA). The appearance of diamond-like domains with strong lateral charges, and of weak stripes structures brings into

Electron Vortex Beams with High Quanta of Orbital Angular Momentum

January 14, 2011
Benjamin James McMorran, Amit K. Agrawal, Ian M. Anderson, Andrew A. Herzing, Henri J. Lezec, Jabez J. McClelland, John Unguris
Analogous to vortices in light optical beams, electron optical beams with helical wavefronts carry orbital angular momentum and promise new capabilities for electron microscopy and other applications. We use nanofabricated diffraction holograms in an

Measuring the effects of low energy ion milling on the magnetization of Co/Pd multilayers using scanning electron microscopy with polarization analysis

April 30, 2010
Benjamin James McMorran, Aaron C. Cochran, Randy K. Dumas, Kai Liu, Paul Morrow, Daniel T. Pierce, John Unguris
The dependence of the magnetic properties of Co/Pd multilayer films with very thin individual layers, Co(0.4nm)/Pd(0.6nm), on the energy of ion milling is investigated using scanning electron microscopy with polarization analysis (SEMPA). The effect of Ar