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1、NEWS & VIEWS nature materials | VOL 6 | JUNE 2007 | 399 SPINTRONICS A nanomagnet oscillator Andrew D. Kent is in the Department of Physics, New York University, 4 Washington Place, New York, New York 10003, USA. e-mail: andy.kentnyu.edu T he connection between electricity and magnetism has a long i
2、llustrative history starting with Oersted who, in 1819, showed that an electrical current passing near a compass needle causes it to rotate and reorient. is is understood as the result of the current producing a magnetic eld that acts on the magnet, tending to align its magnetization direction with
3、the eld. A remarkable recent discovery is that current ow through a magnetic material may alter its magnetization by a mechanism that has nothing to do with magnetic elds. is new mechanism can cause a persistent oscillation of the magnetization in the presence of a constant current, which is not pos
4、sible with the Oersted magnetic elds otherwise associated with electric currents. On page 447 of this issue, Dimitri Houssameddine and colleagues show how to use this mechanism to generate large-amplitude magnetic oscillations at low currents without the need for an applied magnetic eld 1 . eir osci
5、llator makes use of the ow of electron spin and adds to applications of spin-based electronics, or spintronics. A direct electrical current can drive high-frequency oscillations of the magnetization of a nanomagnet. A current-tunable microwave oscillator has now been demonstrated that shows large-am
6、plitude oscillations. thin (1.4 nm), and their length (up to 3 m) and homogeneity is extraordinary. e dynamical template mechanism can explain these results: silica deposition occurs on both sides of the lanreotide molecule, and it stops immediately a er the neutralization of surface charge. is is a
7、 very well-controlled process that yields a hierarchical structure from the nanoscale to the macroscopic level. e double-walled silica tubes form bundles that can be as much as a centimetre long. e importance of this work does not simply lie in the production of a structurally very interesting mater
8、ial. e dynamical template concept has potential applications in a variety of future biomimetic materials syntheses because it allows the production of superstructures greatly exceeding the size of the original template assemblies. erefore, Pouget and colleagues experiments represent an important adv
9、ance because the current biomimetic approaches still fall far short of natures perfection with respect to complexity and uniqueness of the materials obtained. Biomimetic synthesis approaches o er a number of advantages over conventional inorganic synthesis routes. ey usually work in mild chemical co
10、nditions, which usually also implies lower consumption of energy and reduced release of environmentally unfriendly chemicals. Furthermore, it is hoped that biomimetic approaches will pave the way to synthetic routes that, as in the work of Pouget and colleagues, allow ne control of material structur
11、e across di erent length scales. References 1. Pouget, E. et al. Nature Mater. 6, 434439 (2007). 2. Krger, N., Deutzmann, R. & Sumper, M. Science 286, 11291132 (1999). 3. Krger, N., Deutzmann, R., Bergsdorf, C. & Sumper, M. Proc. Natl Acad. Sci. USA 97, 1413314138 (2000). 4. Shimizu, K., Cha, J., St
12、ucky, G. D. & Morse, D. E. Proc. Natl Acad. Sci. USA 95, 62346238 (1998). 5. Valry, C. et al. Proc. Natl Acad. Sci. USA 100, 1025810262 (2003). Figure 1 Biominerals set an example of complexity and functionality. Their syntheses are inspirational to material scientists who explore new chemical route
13、s to make materials. nmat June N&V.indd 399 nmat June N&V.indd 399 10/5/07 14:33:10 10/5/07 14:33:10Research in spintronics has shown that the spin of electrons passing through a magnetic layer becomes partially polarized along the magnetization direction. is favours spin polarization in one particu
14、lar orientation and therefore these ferromagnetic materials act as spin lters for electrical current. Two magnetic layers can then be used as a polarizeranalyser combination for electron spin, in analogy to light passing through a set of polarizing lters. e rst layer polarizes the current and the se
15、cond layer acts as an analyser of the resulting spin-polarization. When the polarizer and analyser magnetizations are aligned in a parallel state (P-state), there is a high transmission of spin-polarized electrons and as a result a low-resistance state. With the layers magnetizations antiparallel (AP-state), the polarizer and analyser are crossed. e result is a reduced electron transmission and a high-resistance state. is is the basis for our understanding of the giant magnetoresistance e ect in magnetic multilayers 2 . When the layer magnetizations are not collinear there are
