Browsing by Author "Nekrashevich, Ivan"
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Item Ferromagnetic Resonance Spectroscopy of Arrays of Coupled Nanomagnets(2016-12) Nekrashevich, Ivan; Litvinov, Dmitri; Brankovic, Stanko R.; Ruchhoeft, Paul; Lubchenko, Vassiliy; Bao, JimingMagnetodynamic properties of large area magnetic nanopatterns are of the great interest for magnetic hard drive storage industry and novel magnetic logic devices. With general trend for miniaturization and increase of areal density of magnetic nanodevices, collective magnetodynamic behavior will play increasingly important role. Thus, understanding and identification of the key factors affecting performance of coupled nanomagnetic system is the crucial part in the future success of magnetism related industries. In this work, we look at phenomena of ferromagnetic and spin wave (SW) resonances in magnetic nanopatterned films. Also, within the scope of this study are conditions of emergence, magnetic properties, and stability of the magnetic vortices in large arrays of Ni19Fe81 (permalloy) dipole coupled nanomagnets. In our experimental studies, we survey magnetodynamic properties and magnetic texture of permalloy nanopatterns by means of the field sweep FMR spectrometry, Alternating Gradient Field Magnetometry, Polar Magneto-Optical Kerr Effect Magnetometry, and Magnetic Force Microscopy. Using electron-beam lithography and lift-off process, we fabricate and characterize magnetic nanopatterned films with a wide range of geometrical parameters such as lateral size of rectangular nanomagnets, nanomagnet aspect ratio and the duty cycle of the square pattern as well as type of 2D lattice. By changing the geometrical parameters of the nanostructures we achieve control over the ferromagnetic and spin-wave resonance modes in patterned films at various directions of external bias magnetic field. Using FMR spectrometry, we measure the critical angles between the DC magnetic field and the plane of the nanopattern at which quantized standing spin wave modes are excited (resonance mode splitting). Our experimental results were supplemented with analytic calculations and micromagnetic simulations. Proposed analytic model allows distinguishing between the observed resonance modes based on effective demagnetizing factors which in their turn represent geometries of individual nanomagnets and geometrical properties of arrays. Our micromagnetic simulations are in good agreement with experimental observations and confirm our assumptions about significant contribution of long range dipolar interdot coupling to magnetic textures and spin wave resonance spectrum of nanodot arrays.Item Magnetic Sensing Potential of Fe3O4 Nanocubes Exceeds That of Fe3O4 Nanospheres(ACS Omega, 2017-11) Kolhatkar, Arati G.; Chen, Yi-Ting; Chinwangso, Pawilai; Nekrashevich, Ivan; Dannangoda, Gamage C.; Singh, Ankit; Jamison, Andrew C.; Zenasni, Oussama; Rusakova, Irene A.; Martirosyan, Karen S.; Litvinov, Dmitri; Xu, Shoujun; Willson, Richard C.; Lee, Randall T.This paper highlights the relation between the shape of iron oxide (Fe3O4) particles and their magnetic sensing ability. We synthesized Fe3O4 nanocubes and nanospheres having tunable sizes via solvothermal and thermal decomposition synthesis reactions, respectively, to obtain samples in which the volumes and body diagonals/diameters were equivalent. Vibrating sample magnetometry (VSM) data showed that the saturation magnetization (Ms) and coercivity of 100�5 nm cubic magnetic nanoparticles (MNPs) were, respectively, 1.4�0 and 1.1�4 times those of spherical MNPs on a same-volume and same-body diagonal/diameter basis. The Curie temperature for the cubic Fe3O4 MNPs for each size was also higher than that of the corresponding spherical MNPs; furthermore, the cubic Fe3O4 MNPs were more crystalline than the corresponding spherical MNPs. For applications relying on both higher contact area and enhanced magnetic properties, higher-Ms Fe3O4 nanocubes offer distinct advantages over Fe3O4 nanospheres of the same-volume or same-body diagonal/diameter. We evaluated the sensing potential of our synthesized MNPs using giant magnetoresistive (GMR) sensing and force-induced remnant magnetization spectroscopy (FIRMS). Preliminary data obtained by GMR sensing confirmed that the nanocubes exhibited a distinct sensitivity advantage over the nanospheres. Similarly, FIRMS data showed that when subjected to the same force at the same initial concentration, a greater number of nanocubes remained bound to the sensor surface because of higher surface contact area. Because greater binding and higher Ms translate to stronger signal and better analytical sensitivity, nanocubes are an attractive alternative to nanospheres in sensing applications.