Unprecedented view of two-dimensional magnets that use diamond quantum sensors.



Unprecedented view of two-dimensional magnets that use diamond quantum sensors.

A quantum diamond sensor is used to determine the magnetic properties of the individual atomic layers of the material chromium triiodide quantitatively. It was shown that the direction of the turns in successive layers alternate in the layers. Credit: University of Basel, Department of Physics.

For the first time, physicists at the University of Basel have been able to measure the magnetic properties of atomically thin Van der Waals materials at the nanoscale. They used quantum diamond sensors to determine the strength of the magnetization of the individual atomic layers of the material chromium triiodide. In addition, they found a long-sought explanation for the unusual magnetic properties of the material. The newspaper Science He has published the results.

The use of two-dimensional, thin and atomic van der Waals materials promises innovations in numerous fields of science and technology. Scientists around the world are constantly exploring new ways of stacking different individual atomic layers and, therefore, designing new materials with unique and emerging properties.

These super thin composite materials are held together by the van der Waals forces and often behave differently from bulk crystals of the same material. The materials of van der Waals atomically thin include insulators, semiconductors, superconductors and some materials with magnetic properties. Its use in spintronics or in ultra-compact magnetic memory media is highly promising.

The first quantitative measurement of magnetization.

Until now, it has not been possible to determine the strength, alignment and structure of these magnets quantitatively or at the nanoscale. The team led by Georg-H.-Endress Professor Patrick Maletinsky of the Department of Physics and the Swiss Institute of Nanoscience at the University of Basel has shown that the use of diamond tips decorated with single-electron turns in an atomic force microscope It is ideal for these types of studies.

"Our method, which uses individual turns in diamond-colored centers as sensors, opens up a completely new field.The magnetic properties of two-dimensional materials can now be studied at the nanoscale and even quantitatively.Our innovative quantum sensors are perfectly suitable for this complex task, "says Maletinsky.

The number of layers is critical.

Using this technology that was originally developed in Basel and is based on a single electron spin, the scientists collaborated with researchers at the University of Geneva to determine the magnetic properties of the individual atomic layers of chromium triiodide (CrI).3). The researchers were able to find the answer to a key scientific question about the magnetism of this material.

As three-dimensional, bulk crystal, the chromium triiodide is completely magnetically ordered. However, in the case of few atomic layers, only batteries with an odd number of atomic layers show a non-zero magnetization. Batteries with an even number of layers exhibit an antiferromagnetic behavior; that is, they are not magnetized. The cause of this "even / odd effect" and the discrepancy with the bulk material was unknown previously.

Tension as a cause

Maletinsky's team was able to demonstrate that this phenomenon is due to the specific atomic arrangement of the layers. During the preparation of the sample, the individual layers of chromium triiodide move slightly against each other. The resulting tension in the lattice means that the spins of the successive layers can not be aligned in the same direction; instead, the direction of rotation alternates in the layers. With an even number of layers, the magnetization of the layers is canceled; with an odd number, the force of the magnetization measured corresponds to that of a single layer.

However, when the tension in the pile is released, for example, when drilling the sample, the turns of all the layers can be aligned in the same direction, as also observed in the crystals in mbad. The magnetic force of the whole stack is then consistent with the sum of the individual layers.

The work done by the Basel scientists not only answers a key question about van der Waals' two-dimensional magnets, but also opens up interesting perspectives on how their innovative quantum sensors can be used in the future to study two-dimensional magnets in order to contribute. To the development of new electronic components.


Advance made in atomically thin magnets.


More information:
L. Thiel et al. Test the magnetism in 2D materials at the nanoscale with single spin microscopy, Science (2019). DOI: 10.1126 / science.aav6926

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University of Basel


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Unprecedented vision of two-dimensional magnets using quantum diamond sensors (2019, April 26)
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