Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session I1: Condensed Matter III |
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Chair: Karine Chesnel, Brigham Young University Room: Science Building 031 |
Saturday, October 18, 2014 10:15AM - 10:39AM |
I1.00001: Stress Control of Magnetic Properties Invited Speaker: Jose De La Venta Controlling the magnetic properties of ferromagnetic (FM) thin films without magnetic fields is an on-going challenge in condensed matter physics with multiple technological implications. External stimuli and proximity effects are the most used methods to control the magnetic properties. An interesting possibility arises when ferromagnets are in proximity to materials that undergo structural phase transition (SPT). The stress associated with the structural changes produces a magnetoelastic anisotropy in proximity coupled ferromagnetic films that allows controlling the magnetic properties without magnetic fields. Canonical examples of materials that undergo SPT and a metal to insulator transitions are the vanadium oxides (VO$_{2}$ and V$_{2}$O$_{3})$. Here I show that the coercivities and magnetizations of the ferromagnetic films grown on vanadium oxides are strongly affected by the phase transition. The changes in coercivity can be as large as 300{\%} and occur in a very narrow temperature interval. These effects can be controlled by the thickness and deposition conditions of the different ferromagnetic films. This work has been done in collaboration with S. Wang, T. Saerbeck, J. G. Ramirez and Ivan K. Schuller, Dept. of Physics, UC San Diego. [Preview Abstract] |
Saturday, October 18, 2014 10:39AM - 10:51AM |
I1.00002: Domain wall chirality of ultrathin magnetic films Anirban Kundu, Shufeng Zhang In conventional ferromagnetic materials, domain wall structure is determined by three competing magnetic interactions: exchange, anisotropy, and magneto-statics. These interactions do not break the degeneracy of domain wall chirality, i.e., the clockwise and anti-clockwise spin rotations of the domain wall are equally probable. It has been recently shown, however, that ultrathin magnetic films with perpendicular magnetic anisotropy favors one of the chiral patterns.\footnote{Gong Chen et al., Nature Communications 4, 2671(2013)} We propose that such chiral symmetry-breaking is due to the interface spin-orbit coupling. By explicitly calculating the effective spin interaction between magnetic ions, mediated by spin-polarized conduction electrons, we find that the resulting indirect exchange interaction is equivalent to the Dzyaloshinskii-Moriya (DM) interaction which is known to be chiral dependent. When we apply the DM interaction along with other magnetic energies to Neel and Bloch domain walls, we are able to map out the preferred domain wall structure with a definitive chirality. An extensive comparison between our theory and the experiment on CoNi thin films is carried out. [Preview Abstract] |
Saturday, October 18, 2014 10:51AM - 11:03AM |
I1.00003: Mapping Magnetic Memory in [Co/Pd]IrMn Thin Films Under Field Cooling Conditions Alex Safsten, Karine Chesnel, Eric Fullerton Certain magnetic thin films exhibit the property of magnetic memory when they meet some specific requirements. Magnetic memory is the ability of the magnetic domains within the film to return to a previous configuration after the film has been magnetically saturated. We found that such films, which present exchange bias properties, show a very high amount of magnetic memory when cooled below their blocking temperature. We have further investigated the effect of cooling conditions on the amount of memory and its behavior throughout the magnetization cycle. I will present the methods we are using to map the magnetic memory throughout the magnetic hysteresis cycle, via magnetic speckle cross-correlations. I will also present results from various experiment and recent synchrotron experiment carried out at APS in July 2014, confirming the occurrence of magnetic memory in [Co/Pd] IrMn exchange bias thin multilayers. [Preview Abstract] |
Saturday, October 18, 2014 11:03AM - 11:15AM |
I1.00004: X-ray Resonant Magnetic Scattering of Fe$_{3}$O$_{4}$ Nanoparticles Dalton Griner, Yanping Cai, Matea Trevino, Karine Chesnel, Roger Harrison, Alex Reid We are studying the magnetic order in Fe$_{3}$O$_{4}$ nanoparticles assemblies. These particles have a variety of applications, some of the more interesting ones being: drug targeting, cancer therapy, and MRI applications. We have recently (summer 2014) 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 used the XMCD signal to extract the spin and orbital magnetic moments in Fe$_{3}$O$_{4}$. In addition, we used 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] |
Saturday, October 18, 2014 11:15AM - 11:27AM |
I1.00005: Optically detected magnetic resonance of silicon vacancies in SiC Kyle Miller Defects occur in a silicon carbide lattice structure where a silicon atom is missing. Spin lifetimes of electrons located at these defects can be studied through optically detected magnetic resonance (ODMR). We have employed traditional ODMR to measure the T$_{2}^{\ast}$ spin lifetime, and pulsed ODMR/spin echoes to measure the T$_{2}$ spin lifetime. We found T$_{2}^{\ast}$ to be about 140 ns at low temperature (6 K), and T$_{2}$ ranges between 5 and 17 $\mu$s as temperature is decreased from 160 K to 6 K. These lifetimes were determined at resonance with a magnetic field of about 372 mT and microwave frequency equal to 10.4744 GHz. Characterization of these lifetimes provides valuable information for use of SiC in quantum computing. [Preview Abstract] |
Saturday, October 18, 2014 11:27AM - 11:39AM |
I1.00006: Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems Nikolai Sinitsyn, Dibyendu Roy, Luyi Yang, Scott Crooker We develop a minimally invasive approach for characterization of inter-species interactions in heterogeneous spin systems by detecting spin fluctuations alone. We consider two spin ensembles in thermal equilibrium that interact via binary exchange coupling and determine cross-correlations between the intrinsic spin fluctuations exhibited by the two spin species. Our theoretical predictions are experimentally confirmed using ``two-color'' optical spin noise spectroscopy on a mixture of interacting Rb and Cs alkali vapors. The results allow us to explore the rates of spin exchange and total spin relaxation under conditions of strict thermodynamic equilibrium. [Preview Abstract] |
Saturday, October 18, 2014 11:39AM - 11:51AM |
I1.00007: Pressure Induced Superconductivity of BaLi$_{4}$ Anne Marie Schaeffer, Scott Temple, Ella Olejnik, Shanti Deemyad We studied the pressure-induced superconductivity of BaLi$_{4}$~up to 53~GPa by means of electrical resistivity in a diamond anvil cell. Superconductivity in BaLi$_{4}$~is first observed at a pressure of 5.4~GPa with a superconducting critical temperature ($T_{\mathrm{c}})$ of 4.5~K. Below 2~GPa, superconductivity is not observed above the minimum temperature achievable in the current study, 2~K. Between 5.4 and 12~GPa, the~$T_{\mathrm{c}}$~increases steeply to its maximum value of 7~K. Above 12~GPa, the pressure dependence of~$T_{\mathrm{c}}$ is complex and the sign of d$T_{\mathrm{c}}$/d$P$~changes several times in going up to the maximum pressure studied, of 53~GPa. [Preview Abstract] |
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