Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B19: Magnetic Nanoparticles and Biomedical ApplicationsFocus
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Sponsoring Units: GMAG DMP Chair: Xuemei Cheng, Bryn Mawr Coll Room: LACC 308A |
Monday, March 5, 2018 11:15AM - 11:27AM |
B19.00001: Understanding magnetic spin structures in core-shell Fe3O4/MnxFe3-xO4 nanoparticle polycrystalline assemblies Yumi Ijiri, Jane Hsieh, Ian Hunt-Isaak, Hillary Pan, Kathryn Krycka, Julie Borchers, Ahmed Abdelgawad, Samuel Oberdick, Sara Majetich Magnetic nanoparticles are critical components for many applications, but it is challenging to understand and tailor the governing intra- and inter-particle magnetic interactions. Here, we report the results of polarization analyzed small-angle neutron scattering (PASANS) experiments designed to explicitly probe such correlations in closed-packed polycrystals of core-shell nanoparticles. From other structural measurements, the particles have an average Fe3O4 core diameter of 6.4 nm with a 0.5 nm thick MnxFe3-xO4 shell, with x ~ 1.0. The PASANS data reveal that a significant portion of the nanoparticle magnetic moments are not aligned in a large applied magnetic field, as has been seen in related materials. More strikingly, this system also displays a prominent inter-particle magnetic Bragg peak with components both parallel and perpendicular to the field. The angular dependence of the PASANS data shows further anomalies, indicating that the degree of magnetic correlation varies in extent with temperature and field. The data are fit against a model of close packed, stacked layers where the layer size and thickness can be adjusted to reflect the competition between dipolar and Zeeman energies. |
Monday, March 5, 2018 11:27AM - 11:39AM |
B19.00002: Iron Oxide Nanoparticle Clusters for Biomedical Applications Shirin Pourmiri, Frank Abel, Vasileios tzitzios, George Hadjipanayis Iron Oxide nanoparticles find a broad range of biomedical applications from T2 MRI contract agents, to hyperthermia cancer treatment. Recently, it was reported that hierarchical assemblies of Fe3O4 particles have much higher SLP/SAR values than the isolated superparamagnetic Fe3O4 nanoparticles.1 |
Monday, March 5, 2018 11:39AM - 12:15PM |
B19.00003: Anisotropic hybrid nanostructures for advanced hyperthermia Invited Speaker: Hariharan Srikanth Magnetic nanoparticles have attracted growing interest in the research community due to their wide range of applications in nanomedicine. In particular, the effective shape, surface and interface anisotropies play important roles in tuning the overall magnetic response of nanoparticle assemblies. Our recent research has shown the importance of tuning the effective anisotropy in nanoparticles through surface, shape and core-shell configurations that can be used to enhance the heating efficiency or specific absorption rate (SAR) in magnetic hyperthermia therapy of cancer. We have developed various methods to controllably change the shape anisotropy as well as interface controlled anisotropy in exchange coupled hybrid nanostructures. Multifunctional hybrid Ag-Fe3O4 nanoclusters have also been studied where a synergistic exploitation of magnetothermal and photothermal properties through AC magnetic fields and laser radiation is possible .The heating efficiency is measured through both calorimetry and AC magnetometry. In addition, we have developed a powerful method to probe the anisotropy using resonant RF susceptibility and correlate with SAR. Our systematic research findings underscore the fact that effective magnetic anisotropy plays a significant role in enhancing the SAR for advanced hyperthermia applications. |
Monday, March 5, 2018 12:15PM - 12:27PM |
B19.00004: Influence of nitrogen dopants on the magnetization of cobalt-nitride clusters Masahiro Sakurai, James Chelikowsky, Cai-Zhuang Wang, Kai-Ming Ho Using a real-space pseudopotential approach within the density-functional theory, which is implemented in the PARSEC code, we show that the magnetization of a cobalt-nitride cluster is significantly affected by nitrogen dopants. In particular, we focus on Co3N clusters with recently-discovered hexagonal P63/mmc and rhombohedral R-3c structures. In a hexagonal Co3N cluster, N dopants promote spin polarization for the Co–3d electrons, leading to a large total magnetic moment, which can be as strong as bulk iron. In contrast, N dopants in a rhombohedral Co3N cluster degrade magnetic moment and the dopants are magnetically ``dead,'' which results in lower total magnetic moments in rhombohedral Co3N clusters. These changes in magnetic moment originate from the difference in an orbital hybridization between the Co–3d and N–2p states. We also examine how the magnetization of a Co3N cluster depends on a N content. We find that the total magnetic moment of a hexagonal Co3N1+x cluster with -0.15 < x < 0.15 is tunable and can be enhanced further by controlling the amount of nitrogen dopants. |
Monday, March 5, 2018 12:27PM - 12:39PM |
B19.00005: Magnetic Switching Behavior of Permalloy Cap Layers on a Self-Assembled Nanosphere Template Alexander Beach, Terence Baker, Jiyeong Gu, Chuhee Kwon Three different nanosphere lithography methods, Langmuir film deposition, drop casting, and vertical evaporation, are attempted to create densely packed monolayers of 930 nm diameter polystyrene nanospheres. Langmuir film deposition is the most promising option, yielding the largest area of uniform monolayer, up to 1 mm by 0.5 mm. There is a large parameter space to explore with Langmuir film deposition, with nanosphere concentration, substrate lifting, and surfactant chemistry being critical parameters that need to be carefully controlled. A 10 nm Permalloy layer is sputter-coated onto the monolayer of nanospheres. The topography of these films is explored using AFM, MFM, and SEM imaging. The magnetic force images reveal magnetic anisotropy over the surface of the sample, while the SEM images reveal that the nanospheres do not always contact each other. Magneto-optical Kerr effect and First Order Reversal Curve measurements are conducted to investigate the magnetic switching behavior of the permalloy cap layer on top of the nanospheres. |
Monday, March 5, 2018 12:39PM - 12:51PM |
B19.00006: Investigation of the electronic and magnetic properties of Ni atoms in organometallic network Bing Liu, Wei-Hua Wang, Jiandong Guo The molecular ligands are known to play vital roles in determining the magnetic property of transition metal atoms. Here by low temperature scanning tunneling microscopy and spectroscopy (STM/STS), we investigated the magnetic properties of Ni atoms coordinated to 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP) molecules on Au(111) substrate. In coordination networks, single Ni atoms and vertically arranged Ni atomic pairs can be accommodated among four adjacent TPyP molecules. The single Ni atoms show Kondo effect. The majority of the Ni pairs show no magnetic signal upon preparation, while the other two types show spin-flip excitations with zero field splitting energy of ~15.40 meV and ~2.67 meV, respectively. The non-magnetized Ni pairs upon preparation show spin-flip excitation in magnetic field. These experiments suggest that the two Ni atoms are antiferromagnetically coupled upon preparation, and can be switched to ferromagnetic coupling by magnetic field. Furthermore, the spatial distributions of the d-orbital of top Ni atom are revealed by STS mapping. Our work provides insights into how various magnetic properties can be realized in organometallic networks, and this coordination network may work as template for future study of magnetic property and magnetic interaction. |
Monday, March 5, 2018 12:51PM - 1:27PM |
B19.00007: Abstract Withdrawn Invited Speaker:
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Monday, March 5, 2018 1:27PM - 1:39PM |
B19.00008: Magnetic Coupling of Fe3C Nanoparticles Within Double-Wall Carbon Nanotubes Dario Niebieskikwiat, Wilson Nieto, Johnny Chimborazo, Antonio Briones-Leon, Oleg Domanov, Hidetsugu Shiozawa, Thomas Pichler, Paola Ayala Studying the novelty of magnetism in carbon nanotubes is still intriguing and it has not been completely explored, despite a number of promising technological applications. In this study, we focus on the magnetic properties of bundles of double-walled, metallic carbon nanotubes with encapsulated cementite (Fe3C) nanoparticles of ~3 nm in length inside their hollow core. These nanoparticles are not unintentional impurities, but have been deliberately introduced to fill the nanotubes with ferromagnetic material. Results of VSM magnetometry of the filled nanotubes give an anisotropy constant of ~3x106 erg/cm3, much larger than the anisotropy of free cementite nanoparticles, indicating a strong magnetic coupling of the nanoparticles with the nanotubes. On the other hand, the calculated activation volume for magnetization reversal, of ~400 nm3, shows that around 300 nanoparticles of cementite are mutually coupled through the conduction electrons of the nanotubes. Considering a spin diffusion length of 130 nm along the direction of the nanotubes, the activation volume suggests that magnetic coupling also occurs between neighboring nanotubes in the direction perpendicular to their axis, with a perpendicular magnetic correlation length of ~5-6 nm, i.e. involving four parallel nanotubes. |
Monday, March 5, 2018 1:39PM - 1:51PM |
B19.00009: Measurements of Thermally Activated Hopping of the Magnetization Over a Barrier in a Mesoscale Permalloy System James Delles, E. Dan Dahlberg Square, permalloy dots with sides 200-250nm and a thickness of 10nm have proven to be a model system for exploring random telegraph noise (RTN)1. One property not explored in these previous studies is the RTN attempt frequency that is expected to follow an Arrhenius Law. We have explored the RTN attempt frequency in similarly sized permalloy dots as a function of temperature and barrier height controlled by an external magnetic field. Using the Arrhenius Law to analyze the RTN attempt frequency, both the characteristic attempt frequency and barrier height were determined as functions of applied magnetic field and temperature. |
Monday, March 5, 2018 1:51PM - 2:03PM |
B19.00010: Sensitive MEMS-based Gradiometer Josh Javor Heart disease is the leading cause of death for Americans, an estimated 6.1 million of which suffer from heart arrhythmias. Detection methods are scarce and expensive, leaving many undetected and unmonitored in the event of severe palpitation. The gold standard detection is the electrocardiogram, which is not available for continuous monitoring and is susceptible to conductive tissue noise and signal attenuation. A competing technology, magnetocardiography, has resurfaced due recent technological advances, which remain hampered by large expense and shielding requirements. To fill the fill this void, we present a pT/cm sensitive, inexpensive magnetometer leveraging decades of engineering in commercially available MEMS technology. Weak electromagnetic signals are detected by mechanically coupling a commercially available, micro-sized, permanent magnet with the proof mass of a capacitive accelerometer, which is highly engineered to sense pN forces. By design, our device measures gradient fields directly and rejects time-varying bias fields. An affordable, real-time cardiac monitoring system could have a profound impact on an otherwise unmonitored field of cardiac disease. |
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