Physics Commons^™

Induced Ferromagnetism In Multilayered Graphene In Proximity With Cofe2o4, Himanshu Verma, Dereje Seifu, Shashi P. Karna, Haiping Hong, Mohindar S. Seehra

Faculty & Staff Scholarship

Composites of anisotropic diamagnetic multilayer Graphene (MLG) and ferrimagnetic CoFe2O4 (CFO) nanoparticles (NPs) were synthesized through a one-step sonication process in the presence of a surfactant. The samples were characterized at ambi- ent using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, magnetic force microscopy (MFM) and magnetometry (vibrating sample magnetometer). An induced ferromagnetism was observed in MLG with saturation magnetization MS = 18 emu/g(MLG). This induced ferromagnetism is attributed to ferrimagnetic CFO uniformly distributed on the surface of diamagnetic MLG. SEM images confirm uniform dense distribu- tion of CFO nanoparticles on MLG. MFM images …

Electrostatic Potential And Valence Modulation In La0.7sr0.3mno3 Thin Films, Robbyn Trappen, A. C. Garcia- Castro, Vu Thanh Tra, Chih-Yeh Huang, Wilfredo Ibarra-Hernandez, James Fitch, Sobhit Singh, Jingling Zhou, Guerau Cabrera, Ying-Hao Chu, James M. Lebeau, Aldo H. Romero, Mikel B. Holcomb

Faculty & Staff Scholarship

The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1–16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected …

Challenge Of Engaging All Students Via Self-Paced Interactive Electronic Learning Tutorials For Introductory Physics, Seth Devore, Emily Marshman, Chandralekha Singh

Faculty & Staff Scholarship

As research-based, self-paced electronic learning tools become increasingly available, a critical issue educators encounter is implementing strategies to ensure that all students engage with them as intended. Here, we first discuss the effectiveness of electronic learning tutorials as self-paced learning tools in large enrollment brick and mortar introductory physics courses and then propose a framework for helping students engage effectively with the learning tools. The tutorials were developed via research in physics education and were found to be effective for a diverse group of introductory physics students in one-on-one implementation. Instructors encouraged the use of these tools in a self-paced …

Exploring The Gender Gap In The Conceptual Survey Of Electricity And Magnetism, Rachel Henderson, Gay Stewart, John Stewart, Lynnette Michaluk, Adrienne Traxler

Faculty & Staff Scholarship

The “gender gap” on various physics conceptual evaluations has been extensively studied. Men’s average pretest scores on the Force Concept Inventory and Force and Motion Conceptual Evaluation are 13% higher than women’s, and post-test scores are on average 12% higher than women’s. This study analyzed the gender differences within the Conceptual Survey of Electricity and Magnetism (CSEM) in which the gender gap has been less well studied and is less consistent. In the current study, data collected from 1407 students (77% men, 23% women) in a calculus-based physics course over ten semesters showed that male students outperformed female students on …

Nature Of Magnetic Ordering In Cobalt‐Based Spinels, Subhash Thota, Sobhit Singh

Faculty & Staff Scholarship

In this chapter, the nature of magnetic ordering in cobalt‐based spinels Co3O4, Co2SnO4, Co2TiO4, and Co2MnO4 is reviewed, and some new results that have not been reported before are presented. A systematic comparative analysis of various results available in the literature is presented with a focus on how occupation of the different cations on the A‐ and B‐sites and their electronic states affect the magnetic properties. This chapter specifically focuses on the issues related to (i) surface and finite‐size effects in pure Co3O4, (ii) magnetic‐compensation effect, (iii) co‐existence of ferrimagnetism and spin‐glass‐like ordering, (iv) giant coercivity (HC) and exchange bias …

Examining The Effects Of Testwiseness In Conceptual Physics Evaluations, Seth Devore, John Stewart, Gay Stewart

Faculty & Staff Scholarship

Testwiseness is defined as the set of cognitive strategies used by a student that is intended to improve his or her score on a test regardless of the test’s subject matter. Questions with elements that may be affected by testwiseness are common in physics assessments, even in those which have been extensively validated and widely used as evaluation tools in physics education research. The potential effect of several elements of testwiseness were analyzed for questions in the Force Concept Inventory (FCI) and Conceptual Survey on Electricity and Magnetism that contain distractors that are predicted to be influenced by testwiseness. This …

Identification Of Photocurrents In Topological Insulators, Derek A. Bas, Rodrigo A. Muniz, Sercan Babakiray, David Lederman, J. E. Sipe, Alan D. Bristow

Faculty & Staff Scholarship

Optical injection and detection of charge currents is an alternative to conventional transport and photoemission measurements, avoiding the necessity of invasive contact that may disturb the system being examined. This is a particular concern for analyzing the surface states of topological insulators. In this work one- and two-color sources of photocurrents are isolated and examined in epitaxial thin films of Bi2Se3. We demonstrate that optical excitation and terahertz detection simultaneously captures one- and two-color photocurrent contributions, which has not been required for other material systems. A method is devised to extract the two components, and in doing so each can …

Evaluation Of Pulmonary And Systemic Toxicity Following Lung Exposure To Graphite Nanoplates: A Member Of The Graphene-Based Nanomaterial Family, Jenny R. Roberts, Robert R. Mercer, Aleksandr B. Stefaniak, Mohindar S. Seehra, Usha K. Geddam, Ishrat S. Chaudhuri, Angelos Kyrlidis, Vamsi K. Kodali, Tina Sager, Allison Kenyon, Suzan A. Bilgesu, Tracy Eye, James F. Scabilloni, Stephen S. Leonard, Natalie R. Fix, Diane Schwegler-Berry, Breanne Y. Farris, Michael G. Wolfarth, Dale W. Porter, Vincent Castranova, Aaron Erdely

Faculty & Staff Scholarship

Background: Graphene, a monolayer of carbon, is an engineered nanomaterial (ENM) with physical and chemical properties that may offer application advantages over other carbonaceous ENMs, such as carbon nanotubes (CNT). The goal of this study was to comparatively assess pulmonary and systemic toxicity of graphite nanoplates, a member of the graphene-based nanomaterial family, with respect to nanoplate size.

Methods: Three sizes of graphite nanoplates [20 μm lateral (Gr20), 5 μm lateral (Gr5), and <2 >μm lateral (Gr1)] ranging from 8–25 nm in thickness were characterized for difference in surface area, structure,, zeta potential, and agglomeration in dispersion medium, the vehicle for …

Reply To Comment On Origin Of Surface Canting Within Fe3o4 Nanoparticles, Kathryn L. Krycka, Julie A. Borchers, R.A. Booth, Yumi Ijiri, K. Hasz, J.J. Rhyne, S.A. Majetich

Faculty & Staff Scholarship

No abstract provided.

Particle Moment Canting In Cofe2o4 Nanoparticles, K. Hasz, Yumi Ijiri, Kathryn L. Krycka, Julie A. Borchers, R.A. Booth, S. Oberdick, S.A. Majetich

Faculty & Staff Scholarship

Polarization-analyzed small-angle neutron scattering methods are used to determine the spin morphology in high crystalline anisotropy, 11 nm diameter CoFe2O4 nanoparticle assemblies with randomly oriented easy axes. In moderate to high magnetic fields, the nanoparticles adopt a uniformly canted structure, rather than forming domains, shells, or other arrangements. The observed canting angles agree quantitatively with those predicted from an energy model dominated by Zeeman and anisotropy competition, with implications for the technological use of such nanoparticles.

Inverted Linear Halbach Array For Separation Of Magnetic Nanoparticles, Yumi Ijiri, Chetan Poudel, P. Stephen Williams, Lee R. Moore, Toru Orita, Maciej Zborowski

Faculty & Staff Scholarship

A linear array of Nd-Fe-B magnets has been designed and constructed in an inverted Halbach configuration for use in separating magnetic nanoparticles. The array provides a large region of relatively low magnetic field, yet high magnetic field gradient in agreement with finite element modeling calculations. The magnet assembly has been combined with a flow channel for magnetic nanoparticle suspensions, such that for an appropriate distance away from the assembly, nanoparticles of higher moment aggregate and accumulate against the channel wall, with lower moment nanoparticles flowing unaffected. The device is demonstrated for iron oxide nanoparticles with diameters of ~5 and 20 …

Velocity-Selective Direct Frequency-Comb Spectroscopy Of Atomic Vapors, Jason E. Stalnaker, S. L. Chen, M. E. Rowan, K. Nguyen, T. Pradhananga, C. A. Palm, Derek F. Jackson Kimball

Faculty & Staff Scholarship

We present an experimental and theoretical investigation of two-photon direct frequency-comb spectroscopy performed through velocity-selective excitation. In particular, we explore the effect of repetition rate on the [formula] two-photon transitions excited in a rubidium atomic vapor cell. The transitions occur via stepwise excitation through the [formula] states by use of the direct output of an optical frequency comb. Experiments were performed with two different frequency combs, one with a repetition rate of [formula] MHz and one with a repetition rate of [formula] MHz. The experimental spectra are compared to each other and to a theoretical model.

Polarization-Analyzed Small-Angle Neutron Scattering. Ii. Mathematical Angular Analysis, Kathryn L. Krycka, Julie A. Borchers, Yumi Ijiri, R.A. Booth, S.A. Majetich

Faculty & Staff Scholarship

Polarization-analyzed small-angle neutron scattering (SANS) is a powerful tool for the study of magnetic morphology with directional sensitivity. Building upon polarized scattering theory, this article presents simplified procedures for the reduction of longitudinally polarized SANS into terms of the three mutually orthogonal magnetic scattering contributions plus a structural contribution. Special emphasis is given to the treatment of anisotropic systems. The meaning and significance of scattering interferences between nuclear and magnetic scattering and between the scattering from magnetic moments projected onto distinct orthogonal axes are discussed in detail. Concise tables summarize the algorithms derived for the most commonly encountered conditions. These …

Which Accelerates Faster – A Falling Ball Or A Porsche?, James D. Rall, Wathiq Abdul-Razzaq

Faculty & Staff Scholarship

An introductory physics experiment has been developed to address the issues seen in conventional physics lab classes including assumption verification, technological dependencies, and real world motivation for the experiment. The experiment has little technology dependence and compares the acceleration due to gravity by using position versus time graphs and the kinematic equation. The students are then asked to compare the acceleration they found to the one of a Porsche car which they seem surprised when they learn about it. This experiment may contribute significantly to the understanding of the concept of acceleration and the appreciation for the force of gravity.

Which Accelerates Faster A Falling Ball Or A Porsche?, James D. Rall, Wathiq Abdul-Razzaq

Faculty & Staff Scholarship

An introductory physics experiment has been developed to address the issues seen in conventional physics lab classes including assumption verification, technological dependencies, and real world motivation for the experiment. The experiment has little technology dependence and compares the acceleration due to gravity by using position versus time graphs and the kinematic equation. The students are then asked to compare the acceleration they found to the one of a Porsche car which they seem surprised when they learn about it. This experiment may contribute significantly to the understanding of the concept of acceleration and the appreciation for the force of gravity.

Core-Shell Magnetic Morphology Of Structurally Uniform Magnetite Nanoparticles, Kathryn L. Krycka, R.A. Booth, C.R. Hogg, Y. Ijiri, Julie A. Borchers, W.C. Chen, S.M. Watson, M. Laver, T.R. Gentile, Liv R. Dedon

Faculty & Staff Scholarship

A new development in small-angle neutron scattering with polarization analysis allows us to directly extract the average spatial distributions of magnetic moments and their correlations with three-dimensional directional sensitivity in any magnetic field. Applied to a collection of spherical magnetite nanoparticles 9.0 nm in diameter, this enhanced method reveals uniformly canted, magnetically active shells in a nominally saturating field of 1.2 T. The shell thickness depends on temperature, and it disappears altogether when the external field is removed, confirming that these canted nanoparticle shells are magnetic, rather than structural, in origin.

Internal Magnetic Structure Of Magnetite Nanoparticles At Low Temperature, Kathryn L. Krycka, Julie A. Borchers, R.A. Booth, C.R. Hogg, Yumi Ijiri, W.C. Chen, S.M. Watson, M. Laver, T.R. Gentile, S. Harris

Faculty & Staff Scholarship

Small-angle neutron scattering with polarization analysis reveals that Fe3O4 nanoparticles with 90 Å diameters have ferrimagnetic moments significantly reduced from that of bulk Fe3O4 at 10 K, nominal saturation. Combined with previous results for an equivalent applied field at 200 K, a core-disordered shell picture of a spatially reduced ferrimagnetic core emerges, even well below the bulk blocking temperature. Zero-field cooling suggests that this magnetic morphology may be intrinsic to the nanoparticle, rather than field induced, at 10 K.