FMR Study of Co/Ti Bilayer Thin Films

. We focused on the interaction between two ferromagnetic cobalt layers through a non-magnetic titanium layer. The magnetic properties of the structure were characterized by ferromagnetic resonance technique (FMR). The data were collected as a function of non-magnetic titanium layer thickness. Co/Ti multilayer (Ti (50 {\AA})/Co(45 {\AA})/Ti(2-40 {\AA})/Co(40 {\AA})/Ti(100 {\AA}))films were grown onto naturally oxidized p-type single crystal Si (100) substrate at UHV condition with magnetron sputtering system at room temperature. The thickness of Ti spacer layer ranges from 2 to 40 {\AA} with 2 {\AA} steps. We did not observe usual optic and acoustic modes; instead we had two broad overlapped peaks for the films ranged from 6 {\AA} to 40 {\AA}. One interesting result was the high anisotropic resonance field values for these films. Exchange coupling between ferromagnetic layers causes shift on resonance field values but these shifts in our samples were much larger than expected. This large anisotropic behavior is not clear at the moment. Our theoretical model was not able to determine a value for the exchange coupling parameter. One reason can be the close thickness values for Co sublayers. The other reason can be the Ti non-magnetic layer. If titanium did not grow layer by layer on cobalt, the cobalt ferromagnetic layers may behave as a single layer. As a result one cannot observe exchange interaction between ferromagnetic layers through non-magnetic spacer.Comment: 6 pages, 5 figure

An Investigation of the Dose Distribution Effect Related with Collimator Angle for VMAT Method

Aim of this study is to investigate the efficacy of dose distribution in eleven prostate cancer patients with single VMAT and double VMAT when varying collimator angle. We generated optimum single and double VMAT treatment plans when collimator angle was 0 degrees. We recalculated single VMAT plans at different collimator angles(0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, 90 degrees) for double VMAT plans(0 degrees-0 degrees, 15 degrees-345 degrees, 30 degrees-330 degrees, 45 degrees-315 degrees, 60 degrees-300 degrees, 75 degrees-285 degrees, 90 degrees-270 degrees) without changing any optimization parameters. HI, DVH and %95 dose coverage of PTV calculated and analyzed. We determined better dose distribution with some collimator angles. Plans were verified using the 2 dimensional ion chamber array Matrixx (R) and 3 dimensional Compass (R) software program. A higher % 95 dose coverage of PTV was found for single VMAT in the 15 degrees collimator angle, for double VMAT in the 60 degrees-300 degrees and 75 degrees-285 degrees collimator angles. Because of lower rectum doses, we suggested 75 degrees-285 degrees. When we compared single and double VMAT's dose distribution, we had better % 95 dose coverage of PTV and lower HI with double VMAT. Our result was significant statistically. These finds are informative for choosing 75 degrees-285 degrees collimator angles in double VMAT plans for prostate cancer

Manipulation of Exchange Coupling in Py/Co/Cr Multi layer Thin Films

The main issue addressed in present study is exchange coupling modification between ferromagnetic layers through non-magnetic spacer layers using extra ultra-thin ferromagnetic layers (Co). In order to achieve this goal, we prepared Cr(50 angstrom) / Py(20 angstrom) / Co(5 angstrom) / Cr(7, 10, 13 angstrom) / Co(5 angstrom) / Py (30 angstrom) / Cr(50 angstrom) / Si using magnetron sputtering at UM' conditions and characterized by Ferromagnetic Resonance (FMR) technique. As the present study results were compared to our previous study on (Py/Cr), the exchange coupling energy was increased ten times with the cobalt thin laye