RESUMEN
Transition metal alloys are essential for magnetic recording, memory, and new materials-by-design applications. Saturation magnetization in these alloys have previously been measured by conventional techniques, for a limited number of samples with discrete compositions, a laborious and time-consuming effort. Here, we propose a method to construct complete saturation magnetization diagrams for Co-Fe-Ni alloys using scanning Hall probe microscopy (SHPM). A composition gradient was created by the diffusion multiple technique, generating a full combinatorial materials library with an identical thermal history. The composition and crystallographic phases of the alloys were identified by integrated energy dispersive X-ray spectroscopy and electron backscatter diffraction. "Pixel-by-pixel" perpendicular components of the magnetic field were converted into maps of saturation magnetization using the inversion matrix technique. The saturation magnetization dependence for the binary alloys was consistent with the Slater-Pauling behavior. By using a significantly denser data point distribution than previously available, the maximum of the Slater-Pauling curve for the Co-Fe alloys was identified at ~ 32 at% of Co. By mapping the entire ternary diagram of Co-Fe-Ni alloys recorded in a single experiment, we have demonstrated that SHPM-in concert with the combinatorial approach-is a powerful high-throughput characterization tool, providing an effective metrology platform to advance the search for new magnetic materials.
RESUMEN
A double percolation transition is identified in a binary network composed of nanoparticles of MgB2 superconductor and CrO2 half-metallic ferromagnet. Anomalously high-resistance or insulating state, as compared to the conducting or superconducting states in single-component systems of either constituent, is observed between two distinct percolation thresholds. This double percolation effect, which is especially pronounced at liquid helium temperatures, is controlled by composite volume fraction and originates from the suppressed interface conduction and tunneling as well as a large geometric disparity between nanoparticles of different species. We investigate the scaling behavior near both percolation thresholds and determine the distinct critical exponents associated with two different types of transitions.
RESUMEN
A new approach to the solution-phase synthesis of manganese antimonide nanoparticles was developed to reduce competitive oxide formation by exploitation of sodium borohydride (NaBH4) (0.53-2.64 mmol) as a sacrificial reductant. However, in the presence of near-stoichiometric precursor amounts of manganese carbonyl and triphenyl antimony, the introduction of NaBH4 results in a different growth mechanism, Solution-Solid-Solid (SSS), leading to tadpole-shaped manganese antimonide nanoparticles with antimony-rich heads and stoichiometric manganese antimonide tails. We hypothesize that a solid antimony-rich manganese antimonide cluster acts as an initiator to tail growth in solution. Notably, the length of the tail correlated with the amount of NaBH4 used. Interestingly, these anisotropic particles can be transformed progressively into spherical-shaped nanoparticles upon the addition of excess manganese carbonyl. The anisotropic manganese antimonide particles possess saturation magnetizations ca. twenty times higher than that reported for MnSb nanoparticles prepared without NaBH4, attributed to limitation of oxidation.