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Graphene's allure can be magnetic: proximity allows carbon sheet to borrow a material's power.

Although atom-thick sheets of carbon called graphene have many extraordinary properties, magnetism isn't one of them. But a new study reveals that graphene can simply borrow the magnetic properties of a nearby material.

The technique, reported in the Jan. 9 Physical Review Letters, creates a magnetic form of graphene by precisely placing it above a magnetic, insulating compound. It's the first time researchers have magnetized graphene while also preserving the ultrathin material's other tantalizing properties, such as the super-speed of electrons coursing through it.

Graphene, discovered in 2004, is valued for its promise in electronics. Its electrons move much faster than those in silicon semiconductors. But it does not exhibit magnetism, which would be useful for certain technological applications.

Yafis Barlas, a theoretical physicist at the University of California, Riverside, and colleagues wondered whether the magnetic compound yttrium iron garnet placed close to graphene would share its magnetism while leaving the carbon sheet's structure and electronic properties intact. To maximize contact between materials, the researchers laid the graphene atop an extremely smooth sample of the yttrium iron garnet, an electric insulator that doesn't interfere with the graphene's electron flow.

The researchers confirmed that the graphene was magnetized by exposing it to an external magnetic field. In nonmagnetic conducting materials, electrical resistance in the direction perpendicular to the current rises steadily as the sample is exposed to a strengthening field. But the resistance in the graphene jumped disproportionately to the strength of the field. This phenomenon, known as the anomalous Hall effect, indicated that the graphene was ferromagnetic, the type of magnetism exhibited by iron and yttrium iron garnet. "The graphene just borrows the magnetic properties," says Allan MacDonald, a condensed matter physicist at the University of Texas at Austin.

He also points out that graphene is not the only promising ultrathin material. He wonders whether the same technique could magnetize a sheet of molybdenum disulfide, a material whose electronic properties resemble those of silicon.

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Title Annotation:MATTER & ENERGY
Author:Grant, Andrew
Publication:Science News
Geographic Code:1USA
Date:Feb 7, 2015
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