Using a smartphone acceleration sensor to study uniform and uniformly accelerated circular motions

The acceleration sensor of a smartphone is used for the study of the uniform and uniformly accelerated circular motions in two experiments. Data collected from both experiments are used for obtaining the angular velocity and the angular acceleration, respectively. Results obtained with the acceleration sensor are shown to be in good agreement with alternative methods, like using video recordings of both experiments and a physical model of the second experiment.Castro-Palacio, JC.; Velazquez, L.; Gómez-Tejedor, JA.; Manjón Herrera, FJ.; Monsoriu Serra, JA. (2014). Using a smartphone acceleration sensor to study uniform and uniformly accelerated circular motions. Revista Brasileira de Ensino de Fisica. 36(2):2315-2315. doi:10.1590/S1806-11172014000200015S2315231536

Longitudinal and polar MOKE magnetometry of magnetoresistive cobalt thin films prepared by thermal evaporation

Cobalt films of thickness 21, 29 and 68 nm were prepared by thermal evaporation with a deposition rate around 0.3 nm/s. Their hysteresis loops from longitudinal and polar magneto-optic Kerr effect (MOKE) magnetometry differed from typical characteristics of uniaxial magnetic anisotropy but still indicated the preference of in-plane anisotropy over perpendicular anisotropy. The longitudinal hysteresis loop of the 68 nm-thick film was decidedly in a transcritical state signified by an enhanced coercive field. Changing the angle (θ) between the 2500 Oe-magnetic field and the current gave rise to the change in electrical resistance (Rθ) of 29 nm-thick film and the plot between Rθ and cos2θ could be linearly fitted. The changes in resistance due to this anisotropic magnetoresistance (AMR) effect ranged from -0.08 % (θ = 90º) to +0.04 % (θ = 0º)

Studies of transport phenomena at ferromagnet/semiconductor interfaces

In order to investigate the viability of spin injection from ferromagnetic contacts into semiconductors, magnetoresistance measurements have been performed on four distinct classes of spin injection devices; two sets of lateral cobalt/silicon/cobalt structures (coded Cornell96 and Cornell97 samples) in which different shape anisotropies cobalt pads were grown on silicon substrates, a set of vertical devices consisting of 1 #mu#m-thick silicon membrane sandwiched by two nickel films and a set of granular cobalt/silicon mechanical milling alloy structures. Negative magnetoresistance due to spin injection into silicon has been observed in the lateral Cornell97 samples at room temperature. The devices also exhibit the spin dependent chemical potential effect at Schottky barriers and the ferromagnetic fringing field Hall effect. While they are also interesting in their own right from both the physics and applications points of view, these effects may obscure spin dependent transport. Furthermore, the observed spin injection effect is modest (0.1-0.3% of magnetoresistance in 16 kOe). As a result, the spin diffusion length cannot be accurately evaluated but can only be estimated to be of order tens of micrometres at the least in n-doped (10"1"8 cm"-"3) silicon. The magnetoresistance characteristic can be modified by the ion milling process. The milled Cornell97 samples show large magnetoresistance (more than 10%) in 4-25 K regime. This may be explained by the introduction of localised states, however this large magnetoresistance whose characteristic is highly temperature-sensitive is not entirely understood. Lorentz magnetoresistance in silicon is a dominant effect in the vertical structures. The giant magnetoresistance has been observed in the cobalt/silicon alloy which can be modelled as the magnetic cobalt granules embedded in non-magnetic cobalt silicide matrix. In addition to these two terminal devices, a novel magnetic transistor comprising a silicon base has been studied. This three terminal device affords the current gain which is not only high (up to 1000) but also magnetically tuneable (up to 0.78% change of gain in 16 kOe field). (author)Available from British Library Document Supply Centre-DSC:D209912 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

EFFECT OF GADOLINIUM SUBSTITUTION ON MAGNETOCALORIC PROPERTIES OF LANTHANUM STRONTIUM MANGANITES

Magnetocaloric effect in sol-gel derived La 0.75-x Gd x Sr 0.25 MnO 3 was studied as a function of temperature and magnetic field. The crystallite size of the rhombohedral manganites was increased and the magnetisation was decreased with increasing Gd doping from x = 0-0.3. By using the indirect measurement, the entropy change computed from temperaturedependent magnetisation was proportional to the applied DC magnetic field. Under the field of 0.7 T, the maximum entropy changes of 0.93-1.14 J/kgK were observed around the Curie temperature (T C ) determined by AC magnetic susceptometry. The T C was decreased with the increase in x. The maximum magnetocaloric effect occured in the sample with x = 0.15 and it could be used in magnetic refrigeration near the room temperature

Electrical Characterization of 65 W Cubic Sonoreactor with Horizontally Stacked Transducers

A sonoreactor was assembled with stacked lead zirconate titanate transducers. These transducers were attached on one side of a 10×10×10 cm3 chamber and driven by an integrated circuit power amplifier. The impedance of the reactor was analyzed in order to determine a matching inductance. The electrical frequency could be varied from 20 to 50 kHz and the electrical output power was adjustable up to 65 W. The highest power was obtained in the case of resonance at 31 kHz and the maximum temperature at the heat sink of the amplifier rose to 42.0ºC. Both acoustic cavitation and mechanical effects could be utilized in this sonoreactor for a variety of purposes including sonochemical synthesis, ultrasonic cleaning and microbial cell disruption

MAGNETIC PROPERTIES OF SPUTTERED COBALT FILMS ON X-RAY LITHOGRAPHIC SUBSTRATES

Arrays of 11.2-16.6 m holes were patterned on 50 m thick SU-8 photoresist layers by using synchrotron X-ray lithography. After the resist development, the chemically stable and mechanically hardened SU-8 templates with varying hole sizes were used as substrates for RF sputtering of 1.5 m-thick cobalt (Co). By comparing hysteresis loops from inplane and out-of-plane magnetisation, the Co film on patterned substrate with average hole size of 16.6 m was more isotropic than in the case of 15.3 and 11.2 m. Both magnetic squareness and coercive field were at the minimum when the holes were smallest. After the removal of Co on SU-8 surfaces, the remaining Co deposits in the holes exhibited smaller squareness and anisotropy. On the other hand, the enhanced coercive field was increased with a reduction in diameter of patterned holes