Faculty-Student Team 2011

Prof. Julian Velev (left) and student Giovanni Baez (front)
(right: Gradstudent Jesuan Betancourt and Milena Bobea)
University of Puerto Rico - Río Piedras
worked with Evgeny Tsymbal, Physics.

"This summer two undergraduate and two graduate students from the University of Puerto Rico participated in the program. We pursued several projects: Using first principle calculations the metastable phases of a given compound can be compared at zero temperature. However, technological applications require room temperature operation. By calculating phonon dispersions from first principles we investigated the thermal stability of various metastable phases of materials of technological importance. In addition, we studied electron transport involving strongly correlated materials in the magnetic tunnel junction or the spin filtering setup. These materials have additional functionalities which could be exploited for technologically important applications such as non-volatile memories and magnetic recording."

Prof. Luis Rosa and student Freddy Wong (middle)
left: REU Physics student Godohaldo Perez
University of Puerto Rico - Humacao
worked with Peter Dowben, Physics.

"Our work this summer consisted on the electronic structure characterization of the polymer blends of Poly(3-hexylthiophene) P3HT and Poly(vinylidene fluoride) PVDF. The blend incorporates two polymer with two distinct physical properties, P3HT is a semiconducting polymer and PVDF a ferroelectric polymer. The blend films were prepared by Langmuir-Blodgett deposition techniques on a gold substrate. By poling the ferroelectric component of the blends we can control the band position and bensing of the semiconducting polymer of the blend."

Prof. Khalid Eid and student Taylor Reid (right)
front: Gradstudent Robert Tolley
Miami University, Ohio
worked with Andrei Sokolov, Physics.

"Our summer research aimed to characterize the interface between the ferromagnetic semiconductor GaMnAs and each of the ferromagnetic metals iron, cobalt, and permalloy (Ni₈₁Fe₁₉). More specifically, our work had two parts: 1) to study the temperature variation of the contact resistance and the possibility to demonstrate the giant magnetoresistance (GMR) effect in micro-patterned metal/GaMnAs bilayers. 2) To study the magnetic coupling between the two ferromagnetic layers using a SQUID magnetometer. The contact resistance studies were performed in the temperature range from below 4K to room temperature, with and without an external magnetic field. While the magnetization of Co and Fe seemed to switch at the same field as GaMnAs, we found no measurable magnetic coupling between Py and the ferromagnetic semiconductor."

Prof. Yung Huh and student Eric Krage
South Dakota State University
worked with David Sellmyer, Physics.

"Eric Krage, a senior physics major is investigating the structural and magnetic properties of novel ferromagnetic alloys along with Dr. Yung Huh, associate professor of Physics from the South Dakota State University. Projects include the growth and characterization of the rare-earth based permanent magnet SmCo_4-x Fe_xB and the high spin polarized room temperature ferromagnetic Mn₂TiSn Heusler alloys. The systematic Fe doping effect was studied on the structural and magnetic properties of SmCo_4-xFe_xB with 0.05 ≤ x ≤ 0.2 using XRD, EDX, SEM, TEM and SQUID magnetometer. SmCo_4-xFe_xB was prepared by arc-melting followed by thermal annealing at 1000 °C for 48 hr. XRD results show that SmCo_4-xFe_xB alloys crystallize into the hexagonal CeCo₄B-type structure with x = 0.05 to 0.20. A maximum coercivity of 30 kOe with a magnetization 70 emu/g was observed in SmCo_4-xFe_xB at 10 K.
Arc-melted Mn₂TiSn compound was prepared and followed by thermal treatment. EDX and XRD analysis revealed its structural properties and the atomic compositions. Magnetization as a function of temperature and magnetic field measured between 5 K and 350 K show that the samples are ferromagnetic at room temperature but the magnetization at 60 kOe (M) and coercivity (H_c) change significantly with temperature. The room temperature M and H_c are 12 emu/g and 220 Oe respectively. Both the M and H_c increase with decreasing temperature and reach 28 emu/g and 760 Oe as temperature reaches 10 K. We note that the M(H) loops are not fully saturated even at 60 kOe. Magnetization as a function of temperature measured between 5 K and 350 K shows that the samples appear to have magnetic transition at around 400 K."

Prof. Mark Plano Clark and student Micah Marvin
Doane College (Crete, NE)
worked with Axel Enders, Physics.

"This summer we are using what we’ve learned in the past two summers to build a second version of our inexpensive scanning tunneling microscope (STM). Version 2 of the STM reduces the long cables to manageable lengths in a compact system that can be more vibrationally isolated. We have succeeded in producing STM images. Our work this summer has also focused on improving the surfaces and the tips. Using information gathered from other groups we are in the process of producing a tip etching station that should allow us to reliably produce sharp tips. With the new tips, clean surfaces, and the new and improved STM we hope to produce good images by the end of the summer. We continue to try to incorporate changes into the STM that will allow colleges and high schools to build/obtain a reliable STM that fits within their budgets."