Exploring the magnetism of a single atom

May 8, 2014, Ecole Polytechnique Federale de Lausanne

Magnetic devices like hard drives, magnetic random access memories (MRAMs), molecular magnets, and quantum computers depend on the manipulation of magnetic properties. In an atom, magnetism arises from the spin and orbital momentum of its electrons. 'Magnetic anisotropy' describes how an atom's magnetic properties depend on the orientation of the electrons' orbits relative to the structure of a material. It also provides directionality and stability to magnetization.

Publishing in Science, researchers led by EPFL combine various experimental and computational methods to measure for the first time the energy needed to change the magnetic anisotropy of a single Cobalt atom. Their methodology and findings can impact a range of fields from fundamental studies of single atom and single molecule magnetism to the design of spintronic device architectures.

Magnetism is used widely in technologies from hard drives to magnetic resonance, and even in quantum computer designs. In theory, every atom or molecule has the potential to be magnetic, since this depends on the movement of its electrons. Electrons move in two ways: Spin, which can loosely be thought as spinning around themselves, and orbit, which refers to an electron's movement around the nucleus of its atom. The spin and orbital motion gives rise to the magnetization, similar to an electric current circulating in a coil and producing a magnetic field. The spinning direction of the electrons therefore defines the direction of the magnetization in a material.

The magnetic properties of a material have a certain 'preference' or 'stubbornness' towards a specific direction. This phenomenon is referred to as 'magnetic anisotropy', and is described as the "directional dependence" of a material's magnetism. Changing this 'preference' requires a certain amount of energy. The total energy corresponding to a material's magnetic anisotropy is a fundamental constraint to the downscaling of magnetic devices like MRAMs, computer hard drives and even quantum computers, which use different as distinct information units, or 'qubits'.

The team of Harald Brune at EPFL, working with scientists at the ETH Zurich, Paul Scherrer Institute, and IBM Almaden Research Center, have developed a method to determine the maximum possible magnetic anisotropy for a single Cobalt atom. Cobalt, which is classed as a 'transition metal', is widely used in the fabrication of permanent magnets as well as in magnetic recording materials for data storage applications.

The researchers used a technique called inelastic electron tunneling spectroscopy to probe the quantum spin states of a single bound to an MgO layer. The technique uses an atom-sized scanning tip that allows the passage (or 'tunneling') of electrons to the bound cobalt atom. When tunneled through, they transferred energy the cobalt atom, inducing changes in its spin properties.

The experiments showed the maximum magnetic anisotropy energy of a single atom (~60 millielectron volts) and the longest spin lifetime for a single transition metal atom. This large anisotropy leads to a remarkable magnetic moment, which has been determined with synchrotron-based measurements at the X-Treme beamline at the Swiss Light Source. Though fundamental, these findings open the way for a better understanding of magnetic anisotropy and present a single-atom model system that can be conceivably used as a future 'qubit'.

"Quantum computing uses quantum states of matter, and are such a quantum state", says Harald Brune. "They have a life-time, and you can use the individual suface adsorbed atoms to make qubits. Our system is a model for such a state. It allows us to optimize the quantum properties, and it is easier than previous ones, because we know exactly where the cobalt atom is in relation to the MgO layer."

Explore further: Electrical control of single atom magnets

More information: Rau IG, Baumann S, Rusponi S, Donati F, Stepanow S, Gragnaniello L, Dreiser J, Piamonteze C, Nolting F, Gangopadhyay S, Albertini OR, Macfarlane RM, Lutz CP, Jones B, Gambardella P, Heinrich AJ, Harald Brune. 2014. Reaching the magnetic anisotropy limit of a 3d metal atom. Science 08 May 2014.

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May 08, 2014
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1.7 / 5 (6) May 09, 2014
In theory, every atom or molecule has the potential to be magnetic, since this depends on the movement of its electrons.

This statement alone is what leads me to believe the gravity is magnetic by nature.
May 09, 2014
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1.8 / 5 (5) May 09, 2014
Hey, the grammar police. Sorry, supposed to be "that gravity". None the less, using mass alone is inadequate to explain some of the anomalies we observe with gravity. I suggest you read something other then the books that your fed in school, history tells us "common knowledge" tends to be wrong sometimes.
May 09, 2014
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2.6 / 5 (5) May 09, 2014
Easy there doc, it was just a typo. Apparently, your learned experience hasn't taught you any manners. Do you have an argument to make or do you just like to get into pissing matches?

May 09, 2014
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May 09, 2014
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Bob Osaka
4.7 / 5 (3) May 12, 2014
Gravity has an attractive force. The repulsive, Mr. Toad , force of gravity has been theorized as inflaton but never been observed, BICEP2's recent observations withstanding. Monopoles appear in Maxwell's equations though they too have never been observed. In string theory the monopole singularity can be a black hole. Most grand unified theories imply a real monopole particle more accurately a range of particles, dyons. Gravity also appears to be monopole. So yes, it may turn out that gravity may have more similarities with electromagnetism than previously thought.

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