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Nanoscale heat conduction across tunnel junctions prepared through natural oxidation of metal electrodes is experimentally studied. The thermal resistance of AlOx tunnel barriers increases linearly with barrier thickness, which is consistent with the prevailing theory of heat conduction in highly disordered materials. Heat conduction across tunnel junctions is strongly impeded by finite thermal resistance at interfaces between barrier and electrode layers, which can be exploited to create superior thermal barrier coatings. The thermal conductivity of nanolaminates consisting of a series of Ta/TaOx tunnel junctions is determined to be well below the minimum thermal conductivity limit. (c) 2005 American Institute of Physics.

Ge-rich GeSbTe alloys allowed overcoming temperature limitations of phase-change memory technology. In this paper, we present a thorough investigation of the structural evolution and the crystallization process of these alloys as a function of increasing temperature in annealing. We highlight the progressive rearrangement of the structure toward the demixing of Ge and GeSbTe phases. In particular, we show the stability of Sb–Te units and the development of Ge–Te bonds around these features. We observe the formation of a transient GeSbTe phase, which is driven by crystallization phenomena, leading to a gradual diffusion and expulsion of Ge. Therefore, the system moves toward the complete separation of Ge and Ge2Sb2Te5 stable phases. Furthermore, we investigate the effect of N-doping in Ge-rich GeSbTe, which induces the formation of Ge–N bonds. Such features are demonstrated to be responsible for a delayed structural reorganization to higher temperatures, thus affecting the entire process of crystallization and phase separation in the alloy. [ABSTRACT FROM AUTHOR]

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs. [ABSTRACT FROM AUTHOR]

The track width performance of giant magnetoresistive (GMR) read heads defined by e-beam lithography was studied in a series of recording tests. Results on longitudinal media showed slow reductions of magnetic versus physical read widths below 100 nm due to spacing loss effects and substantial microtrack widths. These findings led to explorations of different measurement techniques to address the microtrack width issue. Results on perpendicular media showed distinctly narrower magnetic read widths consistent with modeling results assuming negligible microtrack widths. This read width narrowing effect could be another potential advantage for perpendicular media in high density recording. Finally, various parametric effects on track width performance were also explored and compared between perpendicular and longitudinal media. Index Terms--Longitudinal recording, perpendicular recording, spin valves, test and characterization.

Asymmetrically biased Josephson vortex flow transistors (JVFT) were developed using high- and low-temperature superconductor junctions. The high temperature YBaCuO grain boundary junctions were fabricated on MgO 24-degree tilted bicrystals while the low-temperature shunted Nb/AlOx-Al/Nb tunnel junctions were deposited on sapphire. Results show that high-temperature JVFTs may be used as alternatives to SQUID or FET amplifiers in such applications as infrared imaging, NMR and electromagnetic compatibility.

Magnetic recording read heads have been fabricated and tested using a dual-spin-valve (dual-SV) current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) sensor stack. Thin IrMn antiferromagnetic layers are used for top- and bottom-pinned layers, resulting in a total sensor stack height of 50 nm. Operational read heads with physical sensor trackwidths ranging from 60 to 30 nm have been achieved. Successful readback testing is obtained using perpendicular recording media, with observed magnetic read widths as low as 46 nm. Index Terms--Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) read heads, dual spin-valve, magnetic recording.

The magnetic switching of the exchange biased storage layer in thermally assisted magnetic random access memory cells has been studied in the nanosecond time domain. Under reversed static external field, the magnetic tunnel junctions (MTJs) were subjected to current heating pulses long enough to heat the structure above the blocking temperature of the antiferromagnetic layer. The magnetic response of the storage layer was characterized by single-shot real-time measurement of MTJ resistance. The switching of the storage layer exhibits stochastic fluctuations. Nevertheless, using a heating current density of 4.7×106 A/cm2 corresponding to a bias voltage of 1.8 V, the switching takes place in less than 4 ns under 5 mT. Interestingly, the probability of switching versus pulse duration exhibits characteristic periodic steps which are ascribed to a combined effect of the applied field and spin transfer produced by the heating current pulses. [ABSTRACT FROM AUTHOR]

Spin transfer magnetization dynamics have led to considerable advances in Spintronics, including opportunities for new nanoscale radiofrequency devices. Among the new functionalities is the radiofrequency (rf) detection using the spin diode rectification effect in spin torque nano-oscillators (STNOs). In this study, we focus on a new phenomenon, the resonant expulsion of a magnetic vortex in STNOs. This effect is observed when the excitation vortex radius, due to spin torques associated to rf currents, becomes larger than the actual radius of the STNO. This vortex expulsion is leading to a sharp variation of the voltage at the resonant frequency. Here we show that the detected frequency can be tuned by different parameters; furthermore, a simultaneous detection of different rf signals can be achieved by real time measurements with several STNOs having different diameters. This result constitutes a first proof-of-principle towards the development of a new kind of nanoscale rf threshold detector. [ABSTRACT FROM AUTHOR]