World’s Smallest MRI Scan – Performed On Single Atoms

It is incredible how the invention of Magnetic Resonance Imaging (MRI) became an instrument to examine a human’s internal organs nearly three decades after it was discovered independently by Felix Bloch and Edward Purcell. Since then, doctors have depended on MRI scans to examine various body conditions, including brain and spinal cord. An MRI is regularly done at hospitals these days as a part of imaging for diagnostics. A newly developed world’s smallest machine can now image even the individual atoms.

Researchers at the Center for Quantum Nanoscience at the Institute for Basic Science (IBS) at Ewha Woman’s University, South Korea, have taken a major scientific quantum leap by performing the world’s smallest magnetic resonance imaging (MRI). The team has announced that it was an international collaboration with colleagues from IBM Almaden Research Center in San Jose, US in which QNS scientists used their new technique to visualize the magnetic field of single atoms,  in a paper published in the journal Nature Physics on July 1, 2019.

MRI — How does it work?

The MRI machine uses powerful magnets to create a magnetic field around the human body, which in turn changes the rotation of protons inside the nucleus of the body. These then align to the spin in the motion of magnetic fields. Sensors detect the energy released by protons and convert it into an image.

MRI’s detect the density of spins – commonly known as the fundamental magnets in electrons and protons – in the human body. Usually, an MRI scan requires billions and billions of spins to measure the anticipated difference in any diagnosis.  

However, the new conclusions, published in the journal Nature Physics revealed that this process is also now possible for an individual atom on a surface. The researchers were able to image and explore single atoms by scanning across the surface of an atomically sharp metallic tip in a Scanning Tunneling Microscope, a device for probing and imaging individual atoms.

Iron and titanium, the two magnetic elements were investigated in the study. Through accurate preparation of the sample, the atoms were readily observable in the microscope, allowing researchers to use the microscope’s tip like an MRI machine to map the three-dimensional magnetic field created by the atoms with unprecedented resolution. To do so, the researchers attached another spin cluster to the sharp metal tip of their microscope.

Based on the universal physics principle, two spins could either repel or attract each other depending on their relative position. The researchers were able to outline the magnetic interaction by just sweeping the spin cluster’s tip over the atom on the surface.

Lead author of the study, Dr. Philip Willke of QNS said: “It turns out,  the magnetic interaction that was measured depends on the properties of both the spins, the one on the sample and the one on the tip. For example, the signals that we see for titanium atoms is very different from that for iron atoms. This allows us to distinguish between different kind of atoms by their magnetic field signature and makes our technique really very powerful.”

In the future, the research team plans to use their single-atom MRI scanner to map the spin distribution of atoms in more complex structures such as magnetic materials and molecules. “Many magnetic phenomena take place on a nanoscale, including the latest generation of magnetic storage devices,” informs Dr. Yujeong Bae also of QNS, a co-author in this breaking study. “We now plan to study a variety of systems using our nanoscopic MRI.”

There are high expectations for this new study. The ability to examine the magnetic structure on the nanoscale can guide to developments in new materials and drugs. This technique can help scientists to introduce new drugs in biological structures and medicine. Moreover, scientists want to use this kind of MRI to characterize and control quantum systems. This can lead to a better computation scheme known as quantum computation.

MRI scans (4) on top of a titanium atom taken at varying energies. The bright areas in the figure mark positions where the atom’s magnetic field is the same. [Credit: Dr. Philip Willke]

“I am very excited about these results. It is certainly a milestone in this field and has very promising implications for future research,” says Professor A. Heinrich, Director of QNS. “Our ability to map spins and their magnetic field with unimaginable precision, allows us to gain much deeper knowledge about the structure of matter and it opens up new fields of research.”

About QNS

The Center for Quantum Nanoscience (QNS), at Ewha Woman’s University in Seoul (South Korea), is a world-leading research center merging nanoscience and quantum to engineer the quantum future through research. Backed by Korea’s esteemed Institute for Basic Science, which was founded in 2011, the Center for Quantum Nanoscience draws on decades of Director Andreas Heinrich’s (A Boy and His Atom, IBM) scientific leadership to lay the foundation for future technology by exploring the use of quantum behavior atom-by-atom on surfaces with the highest precision possible.

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