Nanomagnetism

Oxides produced by sol-gel

Fig.1. General scheme of the process: (a) from oxide reagents, (b) From nitrate reagents, (c) heat treatment used in the nanocompounds fabrication. (d) Matrix alumina with gel solution for syntheses of nanotubes, before (top) and after (bottom) thermal treatment.

Half-metal NPs produced by PLD

Half-metals (HM) have attracted much interest as promising materials to enhance several kinds of spin-dependent phenomena, since they generate a highly spin-polarized conduction electron due to an energy band gap in one spin-channel at the Fermi level. This property makes these materials very promising for applications on spin-injection and spin-manipulation in spintronic devices. Therefore, the exploration of half-metallic materials with as high spin-polarization as possible at room temperature is critical for developing practical devices with `spin-mediated functionalities’.

Our aim is to optimize half-metals Heusler alloys by changing its morphology (namely producing nanoparticles), and observe the influence of morphology on its physical properties. In brief, to be used in spintronic devices, a half-metal Heusler alloy must have the highest magnetic saturation moment and Curietemperature as possible; as well as to follow the Slater-Pauling rule and, in addition, be ferromagnetic. Nanoparticles of Heusler alloys were deposited by the PLD technique.

FIG.1 (a) high-resolution TEM image of the Fe 2 MnSi nanoparticle with core/shell morphology has a remarkable volume to shell ratio 3,5:1 this specific nanoparticle has a total diameter of 32 nm (V NPs =17150 nm 3 ), while the core has a diameter of 21 nm (V core =4850 nm 3 ). A deeper view into this NP is needed and therefore a closer picture on HRTEM was acquired and is presented on figure1(b). It is possible to clearly see the resolved lattice planes into the core, where the distance d 220 of the (2 2 0)-planes is about 0.2 nm and corresponding Fourier transform pattern.