“Spintronics,” in which both the spin and charge of electrons are used for logic and memory operations, promises an alternate route to traditional semiconductor electronics. A complete logic architecture can be constructed, which uses planar magnetic wires that are less than a micrometer in width. Logical NOT, logical AND, signal fan-out, and signal cross-over elements each have a simple geometric design, and they can be integrated together into one circuit. An additional element for data input allows information to be written to domain-wall logic circuits.

http://science.sciencemag.org/content/sci/309/5741/1688.full.pdf

Magnetic Domain-Wall Logic

The interaction of subpicosecond laser pulses with magnetically ordered materials has developed into a fascinating research topic in modern magnetism. From the discovery of subpicosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40 fs laser pulse, the manipulation of magnetic order by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation, and quantum computation. Understanding the underlying mechanisms implies understanding the interaction of photons with charges, spins, and lattice, and the angular momentum transfer between them. This paper will review the progress in this field of laser manipulation of magnetic order in a systematic way. Starting with a historical introduction, the interaction of light with magnetically ordered matter is discussed. By investigating metals, semiconductors, and dielectrics, the roles of nearly free electrons, charge redistributions, and spin-orbit and spin-lattice interactions can partly be separated, and effects due to heating can be distinguished from those that are not. It will be shown that there is a fundamental distinction between processes that involve the actual absorption of photons and those that do not. It turns out that for the latter, the polarization of light plays an essential role in the manipulation of the magnetic moments at the femtosecond time scale. Thus, circularly and linearly polarized pulses are shown to act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday and inverse Cotton-Mouton effects, respectively. The recent progress in the understanding of magneto-optical effects on the femtosecond time scale together with the mentioned inverse, optomagnetic effects promises a bright future for this field of ultrafast optical manipulation of magnetic order or femtomagnetism.

/pdf/ultrafast-optical-manipulation-of-magnetic-order-2ms2t5k1zo.pdf

Ultrafast optical manipulation of magnetic order

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

Inorganic nanoparticles exhibit size-dependent properties that are of interest for applications ranging from biosensing and catalysis to optics and data storage. They are readily available in a wide variety of discrete compositions and sizes. Shape-selective synthesis strategies now also yield shapes other than nanospheres, such as anisotropic metal nanostructures with interesting optical properties. Here we demonstrate that the previously described photoinduced method for converting silver nanospheres into triangular silver nanocrystals--so-called nanoprisms--can be extended to synthesize relatively monodisperse nanoprisms with desired edge lengths in the 30-120 nm range. The particle growth process is controlled using dual-beam illumination of the nanoparticles, and appears to be driven by surface plasmon excitations. We find that, depending on the illumination wavelengths chosen, the plasmon excitations lead either to fusion of nanoprisms in an edge-selective manner or to the growth of the nanoprisms until they reach their light-controlled final size.

Controlling anisotropic nanoparticle growth through plasmon excitation

We experimentally demonstrate that the magnetization can be reversed in a reproducible manner by a single 40 femtosecond circularly polarized laser pulse, without any applied magnetic field. This optically induced ultrafast magnetization reversal previously believed impossible is the combined result of femtosecond laser heating of the magnetic system to just below the Curie point and circularly polarized light simultaneously acting as a magnetic field. The direction of this opto-magnetic switching is determined only by the helicity of light. This finding reveals an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.

/pdf/all-optical-magnetic-recording-with-circularly-polarized-2osbqqkcfz.pdf

All-optical magnetic recording with circularly polarized light.

Magnetostrictive GMR sensor on flexible polyimide substrates

In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n-doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions.

Characterization of embedded MgO/ferromagnet contacts for spin injection in silicon

We report on the magnetic and transport properties of [IrMn8/CoFe1.5]/AlOx1.2/[CoFe1/NiFe5/CoFe1]/AlOx1.2/[CoFe1.5/IrMn8] (nanometer) double magnetic tunnel junctions (DMTJs) deposited by magnetron sputtering and patterned using optical lithography. The tunnel magnetoresistance (TMR) versus the bias voltage presents a symmetric characteristic, which indicates a good and similar quality of both AlOx barriers. The junctions show a resistance-area product about 35 kΩ μm2, a high TMR at room temperature of 49.5%, and a high bias voltage at which the TMR signal is decreased to half of its maximum value, V1/2DMTJ=1.33 V. Both hard magnetic layers are rigid in negative field up to 51.5 kA/m, while the coercive field of the soft layer is around 1.1 kA/m. The large difference of coercive fields, combined with the large TMR and V1/2, makes these systems very promising for spin electronic devices.

Low tunnel magnetoresistance dependence versus bias voltage in double barrier magnetic tunnel junction

Spin-dependent transport properties are already applied in hard disks, read heads, sensors and metallic magnetic random access memories. Large efforts currently concentrate on new spin-dependent functionalities using either metallic or tunnelling devices. Here, we show the possibility to realize field programmable spin-logic gates. For this purpose, we experimentally demonstrate the feasibility of a two input spin-logic gate, based on spin-dependent tunnelling elements, which can be separately programmed on-chip to form a logic NOR or a NAND function. Key factors in the spin-logic gate functionality and performance are identified from the measurements and are discussed.

Field programmable spin-logic realized with tunnelling-magnetoresistance devices

Picosecond control of coherent magnetisation dynamics in permalloy thin films by picosecond magnetic field pulse shaping

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