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.

Related Stories

Electrical control of single atom magnets

December 8, 2013

The energy needed to change the magnetic orientation of a single atom – which determines its magnetic stability and therefore its usefulness in a variety of future device applications – can be modified by varying the ...

Researchers see rare-earth-like magnetic properties in iron

April 28, 2014

(Phys.org) —Scientists at the Department of Energy's Ames Laboratory have observed magnetic properties typically associated with those observed in rare-earth elements in iron. These properties are observed in a new iron ...

Recommended for you

Neutron stars may hold an answer to neutron puzzle on Earth

August 15, 2018

According to University of Illinois physicist Douglas H. Beck, "Neutrons play some unusual roles in our world. Free neutrons decay in about 900 s but, bound in nuclei, they are stable and make up somewhat more than half the ...

When mixing granular matter, order among disorder

August 14, 2018

Mixing liquids is easy, or at least scientifically understood: a drop of food coloring will eventually mix into a cup of water through diffusion, and a dollop of cream can be mixed into coffee with a spoon through what is ...

How hot is Schrodinger's coffee?

August 14, 2018

A new uncertainty relation, linking the precision with which temperature can be measured and quantum mechanics, has been discovered at the University of Exeter.


Adjust slider to filter visible comments by rank

Display comments: newest first

May 08, 2014
This comment has been removed by a moderator.
4.5 / 5 (2) May 09, 2014
We need to go back to antenna theory to answer these questions, which is what I did several decades ago in analyzing the actions of atoms. The first and most inaccurate assumption is that electromagnetic radiation is spherical in nature. Einstein's theory is based on that assumption, which in turn was based on Maxwell's theory of radiation, and which is only partly correct. Magnetism is caused by the motions of electrons and the movements of their Coulomb fields. Is is easily shown that dipolar fields necessarily bend with motion, since it would be possible to transmit information faster than the speed of light if they didn't. See my technical paper " A Different Picture of Radiation",IEEE Antennas and Propagation Society International Symposium 2003, in which it is shown that the static field bends with the motion of charges. Thus all radiation is transverse in nature, but with a spherical component. As to the atom, the orbit has two orthogonal components and two orthogonal fields.
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
This comment has been removed by a moderator.
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
This comment has been removed by a moderator.
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
This comment has been removed by a moderator.
May 09, 2014
This comment has been removed by a moderator.
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.
not rated yet May 12, 2014
Thank you Bob! I wrote my first book on the subject ("The Secret of Gravity") in 1997. It is based on the Planck electronic model of the atom, and the four-term electrical force equation between two atoms comes very close to that of the force of gravity (the electrical force is slightly higher). It is really quite simple in concept. The problem is in overcoming the accepted theories of the time. I have also had an article published about analyzing atoms using a computer program: "Analyzing Atoms Using the SPICE Computer Program",Computing in Science and Engineering (an IEEE/AIP publication),Vol.14, No. 3, May/June 2012. SPICE is one of the greatest and most successful computer programs in existence. I believe this will be the new method for analyzing the actions between atoms and molecules in the future.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.