Showing papers by "Albert Fert published in 2008"

Nobel Lecture: Origin, development, and future of spintronics

Abstract: Electrons have a charge and a spin, but until recently, charges and spins have been considered separately. In conventional electronics, the charges are manipulated by electric fields but the spins are ignored. Other classical technologies, magnetic recording, for example, are using the spin but only through its macroscopic manifestation, the magnetization of a ferromagnet. This picture started to change in 1988 when the discovery Baibich et al., 1988; Binash et al., 1989 of the giant magnetoresistance GMR of the magnetic multilayers opened the way to an efficient control of the motion of the electrons by acting on their spin through the orientation of a magnetization. This rapidly triggered the development of a new field of research and technology, today called spintronics and, like the GMR, exploiting the influence of the spin on the mobility of the electrons in ferromagnetic materials. Actually, the influence of the spin on the mobility of the electrons in ferromagnetic metals, first suggested by Mott 1936 , had been experimentally demonstrated and theoretically described in my Ph.D. thesis almost 20 years before the discovery of 1988. The GMR was the first step on the road of the exploitation of this influence to control an electrical current. Its application to the read heads of hard disks greatly contributed to the fast rise in the density of stored information and led to the extension of the hard disk technology to consumer’s electronics. Then, the development of spintronics revealed many other phenomena related to the control and manipulation of spin currents. Today this field of research is expanding considerably, with very promising new axes like the phenomena of spin transfer, spintronics with semiconductors, molecular spintronics, or single-electron spintronics.

Coupling Efficiency for Phase Locking of a Spin Transfer Nano-Oscillator to a Microwave Current

Abstract: The phase locking behavior of spin transfer nano-oscillators (STNOs) to an external microwave signal is experimentally studied as a function of the STNO intrinsic parameters. We extract the coupling strength from our data using the derived phase dynamics of a forced STNO. The predicted trends on the coupling strength for phase locking as a function of intrinsic features of the oscillators, i.e., power, linewidth, agility in current, are central to optimize the emitted power in arrays of mutually coupled STNOs.

Origin, development, and future of spintronics (Nobel Lecture).

Abstract: Electrons have a charge and a spin, but until recently, charges and spins have been considered separately. In conventional electronics, the charges are manipulated by electric fields but the spins are ignored. Other classical technologies, such as magnetic recording, use the spin but only through its macroscopic manifestation, the magnetization of a ferromagnet. This picture started to change in 1988 when the discovery of giant magnetoresistance (GMR) of the magnetic multilayers opened the way to efficient control of the motion of the electrons by acting on their spin through the orientation of a magnetization. This rapidly triggered the development of a new field of research and technology, which is today called spintronics and exploits the influence of the spin on the mobility of the electrons in ferromagnetic materials. Actually, the influence of the spin on the mobility of the electrons in ferromagnetic metals, first suggested by Mott, had been experimentally demonstrated and theoretically described in my PhD thesis more than ten years before the discovery in 1988. The discovery of GMR was the first step on the road towards exploiting this influence to control an electrical current. Its application to the read head of hard disks greatly contributed to the fast rise in the density of stored information and led to the extension of hard-disk technology to consumer electronics. Then, the development of spintronics revealed many other phenomena related to the control and manipulation of spin currents. Today this field of research is extending considerably, with very promising new directions such as spin transfer, spintronics with semiconductors, molecular spintronics, or singleelectron spintronics. From the

Magnetism of "Zn,Co…O thin films probed by x-ray absorption spectroscopies

Abstract: We report on the electronic and magnetic properties of Co-doped ZnO thin films investigated by x-ray absorption spectroscopies and element selective magnetometry. For a low Co concentration (around 5%), we evidence a paramagnetic phase clearly correlated to Co2+ ions substituted to Zn in the ZnO matrix. For higher Co concentrations (around 25%), we demonstrate the coexistence of both paramagnetic and ferromagnetic phases. The use of advanced element and orbital selective techniques allows us through the distinct spectral signature of Co in ionic or metallic states to assign the ferromagnetic phase to the presence of Co in a metallic state as a consequence of Co metal clustering in our films.

High domain wall velocity at zero magnetic field induced by low current densities in spin-valve nanostripes

Abstract: Current-induced magnetic domain wall motion at zero magnetic field is observed in the permalloy layer of a spin-valve-based nanostripe using photoemission electron microscopy. The domain wall movement is hampered by pinning sites, but in between them high domain wall velocities (exceeding 150 m/s) are obtained for current densities well below $10^{12} \unit{A/m^2}$, suggesting that these trilayer systems are promising for applications in domain wall devices in case of well controlled pinning positions. Vertical spin currents in these structures provide a potential explanation for the increase in domain wall velocity at low current densities.

Microwave excitations associated with a wavy angular dependence of the spin transfer torque: Model and experiments

Abstract: The spin transfer torque (STT) can lead to a steady precession of magnetization without any external applied field in magnetic spin valves where the magnetic layers have very different spin diffusion lengths. This effect is associated with a nonstandard dependence of the STT, called ``wavy'' angular dependence of the STT (WAD-STT), predicted in the frame of diffusive models of spin transfer. In this paper, we present a complete experimental characterization of the magnetization dynamics in the presence of a WAD-STT. The results are compared to the prediction of the magnetization dynamics obtained by single domain magnetic simulations (macrospin approximation). The macrospin simulations reproduce well the main static and dynamical experimental features and suggest that the dynamical excitations experimentally observed are associated with a large angle out-of-plane precession mode. The present work validates the diffusive models of the spin transfer and underlines the role of the spin accumulation and the spin relaxation effects on the STT.

Oscillatory interlayer exchange and giant magnetoresistance in magnetic multilayers

Abstract: We discuss two properties of magnetic multilayers, namely the giant magnetoresistance effect and the oscillation of the magnetic coupling between magnetic layers as a function of the thickness of the non‐magnetic spacer. They are illustrated by results obtained in Fe/Cr, Co/Cu, and Fe/Cu multilayers, and a review of the theoretical models dealing with these phenomena is given. Finally, some recently developed magnetic nanostructures with promising performance as field sensing devices are briefly described.