Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session D3: Condensed Matter III |
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Chair: Chi Xu, Arizona State University Room: MU202 |
Friday, October 16, 2015 1:50PM - 2:14PM |
D3.00001: Shaping nanoscale magnetic domain memory in ferromagnets by field cooling Invited Speaker: Karine Chesnel Magnetic nanostructures, such as magnetic domains in perpendicular thin ferromagnetic layers, draw an increasing attention for their potential applications in nanotechnologies. Magnetic domain memory (MDM), i.e. the ability for the domain pattern to retrieve its exact same spatial configuration through field cycling, can be particularly useful in magnetic recording technologies. I will show how X-ray synchrotron tools can uniquely help understand the behavior of these magnetic systems at the nanoscale. More particularly, I will review the technique of Coherent X-ray Magnetic Scattering (CXRMS) and how it can be used to measure MDM in thin ferromagnetic films. Because illuminating a magnetic pattern with coherent X-rays produces a speckle scattering pattern that is a unique fingerprint of the magnetic domain configuration (Fig.1), cross-correlating such speckle patterns provides a way to measure MDM. I will present results on [Co/Pd]IrMn exchange bias thin films that exhibit strong MDM (above 95{\%}) when cooled down below their blocking temperature [1]. By mapping the correlation as function of magnetic field, I will show how the behavior of MDM depends on magnetic history and cooling field. We will see that, when zero-field cooled, the MDM reaches its maximum value in the coercive region of the magnetization cycle [2]. We will also see that MDM is fairly robust through field cycling and through heating, all the way up to the blocking temperature [3]. 1. K. Chesnel et al, \textit{Phys. Rev. B} \textbf{78,} 132409 (2008) 2. K. Chesnel et al, \textit{Phys. Rev. B} \textbf{83,} 054436 (2011) 3. K. Chesnel et al, \textit{New Journal of Physics} \textbf{15,} 023016 (2013) [Preview Abstract] |
Friday, October 16, 2015 2:14PM - 2:26PM |
D3.00002: Temperature Dependence of the Coercivity of VO$_{\mathrm{2}}$/Ni Bilayers Joshua Lauzier, Logan Sutton, Jose de la Venta The temperature dependence of the coercivity and magnetization of VO$_{\mathrm{2}}$/Ni bilayers was studied. VO$_{\mathrm{2}}$ exhibits a well-known Structural Phase Transition (SPT) at 330-340 K, from a low temperature monoclinic (M) to a high temperature rutile (R) structure. VO$_{\mathrm{2}}$/Ni bilayers were grown using a magnetron sputtering technique onto different substrates. The magnetic properties were measured using a Vibrating Sample Magnetometer. The SPT of VO$_{\mathrm{2}}$ induces an inverse magnetoelastic effect that strongly modifies the coercivity and magnetization of the Ni films. In addition, the growth conditions allow tuning of the magnetic properties. Ni films deposited in the rutile phase on top of VO$_{\mathrm{2}}$ (M) show an irreversible change in the coercivity after the first cycle through the high temperature phase, with a corresponding change in the surface morphology. On the other hand, the Ni films grown on top of VO$_{\mathrm{2}}$ (R) do not show this irreversibility. These results indicate that: i) magnetic properties of magnetic films are strongly affected by the strain induced by materials that undergo a structural phase transition; and ii) it is possible to control the properties by tuning the growth conditions. [Preview Abstract] |
Friday, October 16, 2015 2:26PM - 2:38PM |
D3.00003: Magnetic Properties of Fe$_{\mathrm{3}}$O$_{\mathrm{4\thinspace }}$Nanoparticle Assemblies Dalton Griner, Karine Chesnel, Dallin Smith, Yanping Cai, Matea Trevino, Alex Reid We are studying magnetic ordering and magnetic properties in Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ nanoparticles assemblies. These particles have a variety of applications, including: drug targeting, cancer therapy and MRI applications. We have recently (in February 2015) performed a synchrotron experiment at SLAC at Stanford, to measure the X-ray magnetic circular dichroism (XMCD) and the X-ray Resonant Magnetic Scattering (XRMS) signal of nanoparticles we freshly prepared. We use the XMCD signal to extract the spin and orbital magnetic moments in Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$. In addition, we use the XRMS patterns to extract a magnetic profile that provides information about the magnetic order in the nanoparticle assembly and its dependency on particle size and concentration. [Preview Abstract] |
Friday, October 16, 2015 2:38PM - 2:50PM |
D3.00004: Computational Modeling of Magnetic Nanoparticle Chains Dallin Smith, Karine Chesnel, Dalton Griner, Yanging Cai, Alex Reid We study the magnetic properties of nanoparticle assemblies, specifically, magnetite (Fe$_{\mathrm{3}}$O$_{\mathrm{4}})$ nanoparticles. My research work is divided in two parts: the experimental measurements, using x-ray magnetic resonant scattering (XRMS) in which the synchrotron x-rays are finely tuned to the resonant frequency of the Fe atoms. At that energy, the magnetic contrast in the scattering signal is enhanced, allowing us to obtain magnetic information. By changing the polarization of the x-rays, we measured the magnetic circular dichroism (XMCD), useful to extract information about spin and orbital moment. We also measured X-ray Resonant Magnetic Scattering (XRMS) patterns from the nanoparticle assemblies. The second part of my work is the computational modeling of the magnetic profiles extracted from the XRMS data. I use MATLAB to model the density function associated with a chain of nanoparticles. By taking the Fourier transform of the density function (whose peak positions corresponds to the spatial periodicity of the nanoparticles), I try to reproduce the XRMS data.~ [Preview Abstract] |
Friday, October 16, 2015 2:50PM - 3:02PM |
D3.00005: Mobility of nanometer-size solutes in water driven by electric field Mohammadhasan Dinpajooh, Dmitry V. Matyushov We investigate the mobility of nanometer-size solutes in water induced by a uniform external electric field. General arguments are presented to show that a closed surface cutting a volume from a polar liquid will carry an effective non-zero surface charge density when preferential orientation of dipoles exists in the interface. This effective charge will experience a non-vanishing drag in an external electric field even in the absence of free charge carriers. Numerical simulations of model solutes are used to estimate the magnitude of the surface charge density. We find it to be comparable to the values typically reported from the mobility measurements. Hydrated ions can potentially carry a significant excess of the effective charge due to over-polarization of the interface. As a result, the electrokinetic charge can significantly deviate from the physical charge of free charge carriers. We propose to test the model by manipulating the polarizability of hydrated semiconductor nanoparticles with light. The inversion of the mobility direction can be achieved by photoexcitation, which increases the nanoparticle polarizability and leads to an inversion of the dipolar orientations of water molecules in the interface. [Preview Abstract] |
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