Magnetoresistance is the change in a material's electrical resistance in response to an applied magnetic field. Materials with large magnetoresistance have found use as magnetic sensors, in magnetic memory, and in hard drives at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures. Here we report the observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide WTe2: 452,700 per cent at 4.5 kelvins in a magnetic field of 14.7 teslas, and 13 million per cent at 0.53 kelvins in a magnetic field of 60 teslas. In contrast with other materials, there is no saturation of the magnetoresistance value even at very high applied fields. Determination of the origin and consequences of this effect, and the fabrication of thin films, nanostructures and devices based on the extremely large positive magnetoresistance of WTe2, will represent a significant new direction in the study of magnetoresistivity.

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A facile thermodecomposition process to synthesize magnetic graphene nanocomposites (MGNCs) is reported. High-resolution transmission electron microscopy and energy filtered elemental mapping revealed a core@double-shell structure of the nanoparticles with crystalline iron as the core, iron oxide as the inner shell and amorphous Si-S-O compound as the outer shell. The MGNCs demonstrate an extremely fast Cr(VI) removal from the wastewater with a high removal efficiency and with an almost complete removal of Cr(VI) within 5 min. The adsorption kinetics follows the pseudo-second-order model and the novel MGNC adsorbent exhibits better Cr(VI) removal efficiency in solutions with low pH. The large saturation magnetization (96.3 emu/g) of the synthesized nanoparticles allows fast separation of the MGNCs from liquid suspension. By using a permanent magnet, the recycling process of both the MGNC adsorbents and the adsorbed Cr(VI) is more energetically and economically sustainable. The significantly reduced treatment time required to remove the Cr(VI) and the applicability in treating the solutions with low pH make MGNCs promising for the efficient removal of heavy metals from the wastewater.

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