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We study the temperature dependence of the magnetization switching fields of single nanoparticles with an improved micro-superconducting quantum interference device (SQUID) technique, that allows us to perform measurements independently of the critical superconducting temperature of the SQUID. A simplified Néel-Brown model that describes the magnetization reversal by thermal activation over a single anisotropy barrier is compared to measurements on a 3 nm cobalt nanoparticle embedded in a niobium matrix. [ABSTRACT FROM AUTHOR]

Radiofrequency vortex spin-transfer oscillators based on magnetic tunnel junctions with very low-resistance area product were investigated. A high power of excitations has been obtained characterized by a power spectral density containing a very sharp peak at the fundamental frequency and a series of harmonics. The observed behavior is ascribed to the combined effect of spin-transfer torque and Oersted-Ampère field generated by the large applied dc current. We furthermore show that the synchronization of a vortex oscillation by applying an ac bias current is mostly efficient when the external frequency is twice the oscillator fundamental frequency. This result is interpreted in terms of a parametric oscillator. [ABSTRACT FROM AUTHOR]

Recent studies in three-dimensional spintronics propose that the Œrsted field plays a significant role in cylindrical nanowires. However, there is no direct report on its impact on magnetic textures. Here, we use time-resolved scanning transmission x-ray microscopy to image the dynamic response of magnetization in cylindrical Co30Ni70 nanowires subjected to nanosecond Œrsted field pulses. We observe the tilting of longitudinally magnetized domains toward the azimuthal Œrsted field direction and create a robust model to reproduce the differential magnetic contrasts and extract the angle of tilt. Furthermore, we report the compression and expansion, or breathing, of a Bloch-point domain wall that occurs when weak pulses with opposite signs are applied. We expect that this work lays the foundation for and provides an incentive to further studying complex and fascinating magnetization dynamics in nanowires, especially the predicted ultra-fast domain wall motion and associated spin wave emissions. [ABSTRACT FROM AUTHOR]

Microwave-assisted switching of the magnetization is an efficient way to reduce the magnetic field required to reverse the magnetization of nanostructures. Here, the phase sensitivity of microwave-assisted switching of an individual cobalt nanoparticle is studied using a pump-probe technique. The pump microwave pulse prepares an initial state of the magnetization, and the probe pulse tests its stability against switching. Precession states are established, which are stable against switching. Their basin of attraction is measured and is in qualitative agreement with numerical macrospin calculations. The damping parameter is evaluated using the variable delay pump-probe technique. [ABSTRACT FROM AUTHOR]

Spintronics materials have recently been considered for radio-frequency devices such as oscillators by exploiting the transfer of spin angular momentum between a spin-polarized electrical current and the magnetic nanostructure it passes through. While previous spin-transfer oscillators (STOs) were based on in-plane magnetized structures, here we present the realization of an STO that contains a perpendicular spin current polarizer combined with an in-plane magnetized free layer. This device is characterized by high-frequency oscillations of the free-layer magnetization, consistent with out-of-plane steady-state precessions induced at the threshold current by a spin-transfer torque from perpendicularly polarized electrons. The results are summarized in static and dynamic current–field state diagrams and will be of importance for the design of STOs with enhanced output signals. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic state diagram for spin current-induced magnetization dynamics is presented for an out-of-plane magnetized (perpendicular) polarizer and an in-plane magnetized (planar) free layer as obtained from macrospin simulations. The state boundaries are compared upon using a constant spin polarization factor with an angular-dependent spin polarization factor g(θ MP) as introduced by Slonczewski. While two critical boundaries remain unaffected by the angular dependence of the polarization, the transition from precession to an out-of-plane stable state is drastically shifted and shows a strong asymmetry with respect to the sign of the spin-polarized current. [Copyright &y& Elsevier]