Monthly Archives: August 2021

It’s not your grandmother’s fridge magnet.

An exotic form of magnetism has been discovered and linked to an equally exotic type of electrons, according to scientists who analyzed a new crystal in which they appear at the National Institute of Standards and Technology (NIST). Magnetism is created and protected by the crystal’s unique electronic structure, providing a mechanism that could be exploited for fast and robust information storage devices.

The newly invented material has an unusual structure that conducts electricity but causes the flowing electrons to behave like massless particles, the magnetism of which is related to the direction of their movement. In other materials, such as Weyl electrons

have given rise to new behaviors related to electrical conductivity. In this case, however, the electrons promote the spontaneous formation of a magnetic spiral.

“Our research shows a rare example of these particles causing collective magnetism,” said Collin Broholm, a physicist at Johns Hopkins University who led experimental work at the NIST Center for Neutron Research (NCNR). “Our experiment illustrates a unique form of magnetism that can originate from Weyl electrons.”

The conclusions, which appear in Natural materials, reveal a complex relationship between the material, the electrons which pass through it in the form of current and the magnetism exhibited by the material.

This “semi-metal” crystal is made up of repeating unit cells such as the one on the left, which has a square top and rectangular sides. The spheres represent atoms of silicon (purple), aluminum (turquoise) and, in gold, neodymium (Nd), the latter of which are magnetic. Understanding the special magnetic properties of the material requires nine of these unit cells, represented by the larger block on the right (which has a single unit cell framed in red). This 3 × 3 block shows green “Weyl” electrons moving diagonally across the tops of cells and affecting the orientation of the magnetic spin of Nd atoms. A special property of the Weyl electron is the locking of its spin direction, which is either parallel or antiparallel to the direction of its motion, as represented by the small arrows in Weyl electrons. As these electrons move along the four Nd gold atoms, the Nd spins reorient themselves into a “spin spiral” which can be imagined as successively pointing in the 12 o’clock direction (closest to the viewer with the red arrow pointing up), 4 o’clock clock (blue arrow), 8 o’clock (also in blue) and another 12 o’clock (furthest from viewer and again in red). Lines of Nd atoms extend through many layers of the crystal, providing many examples of this unusual magnetic pattern. Credit: N. Hanacek / NIST

In a refrigerator magnet, we sometimes imagine each of its iron atoms as being pierced with a bar magnet with its “north” pole pointing in a certain direction. This image refers to the spin orientations of atoms, which line up in parallel. The material studied by the team is different. It is a “semi-metal” composed of silicon and the metals aluminum and neodymium. Together, these three elements form a crystal, which implies that its component atoms are arranged in a regular repeating pattern. However, it is a crystal that breaks inversion symmetry, meaning that the repeating pattern is different on one side of the unit cells of a crystal – the smallest building block in a crystal lattice – from the other. This arrangement stabilizes the electrons flowing through the crystal, which in turn causes unusual behavior in its magnetism.

The stability of electrons is manifested by uniformity in the direction of their spins. In most electrically conductive materials, such as copper wire, the electrons passing through the wire have spins that point in random directions. This is not the case in the semi-metal, whose broken symmetry transforms the flowing electrons into Weyl electrons whose spins are oriented either in the direction of movement of the electron, or in the exact opposite direction. . It is this locking of the spins of the Weyl electrons in their direction of motion – their momentum – that causes the rare magnetic behavior of the semi-metal.

“Our experiment illustrates a unique form of magnetism that can originate from Weyl electrons.” – Collin Broholm, physicist at Johns Hopkins University

The three types of atoms in the material all conduct electricity, providing stepping stones for electrons as they jump from atom to the atom. However, only neodymium (Nd) atoms exhibit magnetism. They are sensitive to the influence of Weyl electrons, which curiously push the spins of the Nd atom. Look along any row of Nd atoms that runs diagonally across the semi-metal, and you’ll see what the research team calls a “spinning spiral.”

“A simplified way to imagine it is for the first Nd atom to point at 12 o’clock, then the next at 4 o’clock, then the third at 8 o’clock,” Broholm said. “Then the pattern repeats. This beautiful spin “texture” is driven by Weyl electrons when they visit neighboring Nd atoms. “

It took a collaboration between many groups within the Institute for Quantum Matter at Johns Hopkins University to reveal the special magnetism appearing in the crystal. It included groups working on crystal synthesis, sophisticated numerical calculations, and neutron scattering experiments.

“For neutron scattering, we have benefited greatly from the large amount of neutron diffraction beam time available to us at the NIST Center for Neutron Research,” said Jonathan Gaudet, one of the co-authors of the article. . “Without the beam time, we would have missed out on this great physical news.”

Each loop of the spinning spiral is approximately 150 nanometers long, and the spirals only appear at cold temperatures below 7 K. Broholm said that there are materials with similar physical properties that work at room temperature. , and that they could be exploited to create effective magnetic properties. memory devices.

“Magnetic memory technology like hard drives generally requires you to create a magnetic field for them to work,” he said. “With this class of materials, you can store information without needing to apply or sense a magnetic field. Reading and writing information electrically is faster and more robust.

Understanding the effects Weyl electrons cause could also shed light on other materials that have left physicists in consternation.

“Basically, we might be able to create a variety of materials that have different internal rotational characteristics – and maybe we already have it,” Broholm said. “As a community, we have created a lot of magnetic structures that we don’t immediately understand. After seeing the special character of Weyl-mediated magnetism, we may finally be able to understand and use such exotic magnetic structures. ”

Reference: “Weyl-mediated helic magnetism in NdAlSi” by Jonathan Gaudet, Hung-Yu Yang, Santu Baidya, Baozhu Lu, Guangyong Xu, Yang Zhao, Jose A. Rodriguez-Rivera, Christina M. Hoffmann, David E. Graf, Darius H. Torchinsky, Predrag Nikolić, David Vanderbilt, Fazel Tafti and Collin L. Broholm, August 19, 2021, Natural materials.
DOI: 10.1038 / s41563-021-01062-8

The study data was obtained in part with the Multi-Axis Crystal Spectrometer (MACS), which is part of the Center for High Resolution Neutron Scattering (CHRNS), a national user facility jointly funded by the NCNR and the National Science Foundation (NSF).

This “semi-metal” crystal is made up of repeating unit cells such as the one on the left, which has a square top and rectangular sides. The spheres represent atoms of silicon (purple), aluminum (turquoise) and, in gold, neodymium (Nd), the latter of which are magnetic. Understanding the special magnetic properties of the material requires nine of these unit cells, represented by the larger block on the right (which has a single unit cell framed in red). This 3 × 3 block shows green “Weyl” electrons traveling diagonally across the tops of cells and affecting the orientation of the magnetic spin of Nd atoms. A special property of the Weyl electron is the locking of its spin direction, which is either parallel or antiparallel to the direction of its motion, as represented by the small arrows in Weyl electrons. As these electrons move along the four Nd gold atoms, the Nd spins reorient themselves into a “spin spiral”, which can be imagined as pointing successively in the direction of 12 o’clock (closest viewer with the red arrow pointing up), 4 o ‘clock (blue arrow), 8 o’clock (also in blue) and another 12 o’clock (furthest from viewer and again in red). Lines of Nd atoms extend through many layers of the crystal, providing many examples of this unusual magnetic pattern. Courtesy/N. Hanacek / NIST

NIST News:

An exotic form of magnetism has been discovered and linked to an equally exotic type of electrons, according to scientists who analyzed a new crystal in which they appear at the National Institute of Standards and Technology (NIST).

Magnetism is created and protected by the crystal’s unique electronic structure, providing a mechanism that could be exploited for fast and robust information storage devices.

The newly invented material has an unusual structure that conducts electricity but causes the flowing electrons to behave like massless particles, the magnetism of which is related to the direction of their movement. In other materials, such Weyl electrons have given rise to new behaviors related to electrical conductivity. In this case, however, the electrons promote the spontaneous formation of a magnetic spiral.

“Our research shows a rare example of these particles causing collective magnetism,” said Collin Broholm, a physicist at Johns Hopkins University who led experimental work at the NIST Center for Neutron Research (NCNR). “Our experiment illustrates a unique form of magnetism that can originate from Weyl electrons.”

The conclusions, which appear in Natural materials, reveal a complex relationship between the material, the electrons that flow through it as current, and the magnetism that the material exhibits.

In a refrigerator magnet, we sometimes imagine each of its iron atoms as being pierced with a bar magnet with its “north” pole pointing in a certain direction. This image refers to the spin orientations of atoms, which line up in parallel. The material studied by the team is different. It is a “semi-metal” composed of silicon and the metals aluminum and neodymium.

Together, these three elements form a crystal, which implies that its component atoms are arranged in a regular repeating pattern. However, it is a crystal that breaks inversion symmetry, meaning that the repeating pattern is different on one side of the unit cells of a crystal – the smallest building block in a crystal lattice – from the other. This arrangement stabilizes the electrons flowing through the crystal, which in turn causes unusual behavior in its magnetism.

The stability of electrons is manifested by uniformity in the direction of their spins. In most electrically conductive materials, such as copper wire, the electrons passing through the wire have spins that point in random directions. This is not the case in the semi-metal, whose broken symmetry transforms the flowing electrons into Weyl electrons whose spins are oriented either in the direction of movement of the electron, or in the exact opposite direction. . It is this locking of the spins of the Weyl electrons in their direction of motion – their momentum – that causes the rare magnetic behavior of the semi-metal.

“Our experiment illustrates a unique form of magnetism that can originate from Weyl electrons,” Broholm said.

The three types of atoms in material all conduct electricity, providing stepping stones for electrons as they leap from atom to atom. However, only neodymium (Nd) atoms exhibit magnetism. They are sensitive to the influence of Weyl electrons, which curiously push the spins of the Nd atom. Look along any row of Nd atoms that runs diagonally across the semi-metal, and you’ll see what the research team calls a “spinning spiral.”

“A simplified way to imagine it is for the first Nd atom to point at 12 o’clock, then the next at 4 o’clock, then the third at 8 o’clock,” Broholm said. “Then the pattern repeats. This beautiful spin “texture” is driven by Weyl electrons when they visit neighboring Nd atoms. “

It took a collaboration between many groups within the Institute for Quantum Matter at Johns Hopkins University to reveal the special magnetism appearing in the crystal. It included groups working on crystal synthesis, sophisticated numerical calculations, and neutron scattering experiments.

“For neutron scattering, we have benefited greatly from the large amount of neutron diffraction beam time available to us at the NIST Center for Neutron Research,” said Jonathan Gaudet, one of the co-authors of the article. . “Without the beam time, we would have missed out on this great physical news.”

Each loop of the spinning spiral is approximately 150 nanometers long, and the spirals only appear at cold temperatures below 7 K. Broholm said that there are materials with similar physical properties that work at room temperature. , and that they could be exploited to create effective magnetic properties. memory devices.

“Magnetic memory technology like hard drives generally requires you to create a magnetic field for them to work,” he said. “With this class of materials, you can store information without needing to apply or sense a magnetic field. Reading and writing information electrically is faster and more robust.

Understanding the effects Weyl electrons cause could also shed light on other materials that have left physicists in consternation.

“Basically, we might be able to create a variety of materials that have different internal rotational characteristics – and maybe we already have it,” Broholm said. “As a community, we have created a lot of magnetic structures that we don’t immediately understand. After seeing the special character of Weyl-mediated magnetism, we may finally be able to understand and use such exotic magnetic structures. ”

Study data was obtained in part with the multi-axis crystal spectrometer (MAC), which is part of the High Resolution Neutron Scattering Center (CHRN), a national user facility jointly funded by the NCNR and the National Science Foundation (NSF).

An exotic form of magnetism has been discovered and linked to an equally exotic type of electrons, according to scientists who analyzed a new crystal in which they appear at the National Institute of Standards and Technology (NIST). Magnetism is created and protected by the crystal’s unique electronic structure, providing a mechanism that could be exploited for fast and robust information storage devices.

The newly invented material has an unusual structure that conducts electricity but causes the flowing electrons to behave like massless particles, the magnetism of which is related to the direction of their movement. In other materials, these Weyl electrons have given rise to new behaviors related to electrical conductivity. In this case, however, the electrons promote the spontaneous formation of a magnetic spiral.

“Our research shows a rare example of these particles causing collective magnetism,” said Collin Broholm, a physicist at Johns Hopkins University who led experimental work at the NIST Center for Neutron Research (NCNR). “Our experiment illustrates a unique form of magnetism that can originate from Weyl electrons.”

The conclusions, which appear in Natural materials, reveal a complex relationship between the material, the electrons which pass through it in the form of current and the magnetism exhibited by the material.

In a fridge magnet, we sometimes imagine each of its iron atoms as having a bar magnet piercing it with its “north” pole pointing in a certain direction. This image refers to the spin orientations of atoms, which line up in parallel. The material studied by the team is different. It is a “semi-metal” composed of silicon and the metals aluminum and neodymium. Together, these three elements form a crystal, which implies that its component atoms are arranged in a regular repeating pattern. However, it is a crystal that breaks inversion symmetry, which means that the repeating pattern is different on one side of the unit cells of a crystal – the smallest building block of a crystal lattice – than it is on one side. ‘other. This arrangement stabilizes the electrons flowing through the crystal, which in turn results in unusual behavior in its magnetism.

The stability of electrons is manifested by uniformity in the direction of their spins. In most electrically conductive materials, such as copper wire, the electrons passing through the wire have spins that point in random directions. This is not the case in the semi-metal, whose broken symmetry transforms the flowing electrons into Weyl electrons whose spins are oriented either in the direction of movement of the electron, or in the exact opposite direction. . It is this locking of the spins of Weyl electrons in their direction of motion – their momentum – that causes the rare magnetic behavior of the semi-metal.

The three types of atoms in material all conduct electricity, providing stepping stones for electrons as they leap from atom to atom. However, only neodymium (Nd) atoms exhibit magnetism. They are sensitive to the influence of Weyl electrons, which curiously push the spins of the Nd atom. Look along any row of Nd atoms that runs diagonally across the semi-metal, and you’ll see what the research team calls a “spinning spiral.”

“A simplified way to imagine it is for the first Nd atom to point at 12 o’clock, then the next at 4 o’clock, then the third at 8 o’clock,” Broholm said. “Then the pattern repeats. This beautiful spin ‘texture’ is driven by Weyl electrons as they visit neighboring Nd atoms.”

It took a collaboration between many groups within the Institute for Quantum Matter at Johns Hopkins University to reveal the special magnetism appearing in the crystal. It included groups working on crystal synthesis, sophisticated numerical calculations, and neutron scattering experiments.

“For neutron scattering, we have benefited greatly from the large amount of neutron diffraction beam time available to us at the NIST Center for Neutron Research,” said Jonathan Gaudet, one of the co-authors of the article. . “Without the beam time, we would have missed out on this great physical news.”

Each loop of the spinning spiral is approximately 150 nanometers long, and the spirals only appear at cold temperatures below 7 K. Broholm said that there are materials with similar physical properties that work at room temperature. , and that they could be exploited to create effective magnetic properties. memory devices.

“Magnetic memory technology like hard drives typically requires you to create a magnetic field for them to work,” he said. “With this class of materials, you can store information without the need to apply or sense a magnetic field. Electrical reading and writing of information is faster and more robust.”

Understanding the effects Weyl electrons cause could also shed light on other materials that have left physicists in consternation.

“Basically, we might be able to create a variety of materials that have different internal rotational characteristics – and maybe we already have it,” Broholm said. “As a community, we have created many magnetic structures that we do not immediately understand. Having seen the special character of Weyl-mediated magnetism, we may finally be able to understand and use such exotic magnetic structures.”

Reach the cosmos with invisible tendrils, the magnetism is both worldly and worldly.

These forces can pin a photo on your fridge or even rise up from the Earth’s poles to fight against the solar wind, and now a new study published in the journal Proceedings of the National Academy of Sciences shows that magnetism can also help us study the past.

Like fingerprints left on glass, pieces of clay or stone retain in them the memory of the terrestrial magnetism of a long time ago. And now scientists have found a way to reveal these secrets inside pieces of flint, one of the most common materials in history. This includes the oldest magnetic intensity data from the Levant region to date.

Lisa Ratee is professor of paleomagnetics at the University of California at San Diego and co-author of the new study. In addition to helping future researchers date historic sites in the Levant, studying the magnetism of these materials may also help researchers study what Ratee calls a “roller coaster” of magnetic activity on ancient Earth specific to the Levant region, the location of present-day Jordan.

“Our oldest specimens suggest field strengths of around two-thirds of our current field,” says Ratee Reverse. “Then the field grew until about 3,000 years ago, when it was about twice as large as it is today. Since then it has fallen on a roller coaster ride to the terrain today.

This roller coaster ride is known to scientists as the “Levantine Iron Age Anomaly”. Studying such magnetic events may even help us in our own climate change crusade, other research has suggested.

What’s new – While the study of ancient magnetism may not be a household name like carbon dating, Ratee says the technique is far from new. In the past, it was mainly used to study pieces of pottery. This is because pottery is fired at temperatures high enough to take this electromagnetic imprint – or “residual thermal magnetization”.

“When something cools in a magnetic field, it becomes magnetic with a force proportional to the field in which it has cooled,” says Ratee.

However, relying on pottery shards as the sole source of RMR can be uncertain, especially when trying to explore pre-pottery civilizations. That is why Ratee and his colleagues instead focused on a more ubiquitous material: flint.

Typically, flint would not be considered useful at all, Ratee says, because it is not always heated before being used as pottery. However, in this study, they developed a method to first determine whether or not flint samples were fired, and then applied the same analysis typically used on pottery to study its magnetism.

Ratee says this new approach means the team does not “have to waste their time in the future on flints that have never been fired.”

Why is this important – Incorporating flint into the catalog of paleomagnetism could help scientists not only better study the Levantine anomaly, but potentially even better understand the life of these civilizations in general, including their way of eating.

These sites are “important for understanding a number of issues in global archeology,” write the authors. “Including the origins of the village as a type of settlement, the domestication of plants and animals and the rise of the Mediterranean diet.”

How they did it – In their analysis, the team examined 129 flint samples from archaeological sites across modern Jordan dating between 7752 and 5069 BCE.

To determine the intensity of their magnetism, they used something called the IZZI protocol which essentially requires heating samples and comparing the strength of their magnetic fields with the current magnetism of the Earth.

By comparing the magnetism of these samples to known levels of magnetism throughout history, this technique can then be used in the same way as carbon dating.

And after – With the door now open to the use of flint worldwide as a record of ancient magnetism, the next steps in this research will be to build a more solid idea of ​​how magnetism has changed in other parts of the world, Ratee explains.

“In the Middle East, we have a really good idea of ​​what the estate has done in the past,” says Ratee. “The archaeomagnetic community is working to improve records around the world so that they can be applied with increasing confidence elsewhere.”

Ratee’s focus is initially on the Southwestern United States and Southeast Asia.

Abstract: The limitation of the secular variation of the strength of the Earth’s magnetic field in the past is fundamental to understanding the short-term processes of geodynamics. Such records are also a powerful and independent dating tool for archaeological sites and geological formations. In this study, we present 11 robust archaeointensity results from pre-pottery to Jordanian Neolithic pottery that are based on clay and flint (chert) artifacts. Two of these results constitute the oldest archaeointensity data for the entire Levant, ancient Egypt, Turkey and Mesopotamia, extending the archaeomagnetic reference curve for the Holocene. Virtual Axial Dipole Moments (VADM) show that the Earth’s magnetic field in the southern Levant was weak (about two-thirds of the current field) around 7600 BCE, regaining strength to a level higher than the current field around 7000 BCE. , and gradually weakening again around 5200 BCE. In addition, convincing results obtained from burnt flint demonstrate the potential of this very common material, yet rarely used, in archaeomagnetic research, in particular for prehistoric periods ranging from the first use of fire to the invention of pottery.