Nov 27 2019
Quasicrystals are one of the most unusual structures in nature. Thanks to their characteristics, which make them crystal-like yet highly unique, they have been drawing the interest of researchers ever since they were first detected.
In an innovative study, a team of researchers in Japan demonstrated exclusive magnetic transitions in structures similar to quasicrystals. This is a great success in the field of materials science, as it paves the way to advancements in quasicrystal research and several prospective applications.
In the materials science field, many are familiar with crystals—extremely ordered structures where atoms are arranged in a constrained and periodic manner (wherein the atomic arrangement is repeated). However, not many people are acquainted with quasicrystals, which are exclusive structures with unusual atomic arrangement.
Similar to crystals, quasicrystals are also tightly packed, but what is unique about them is the fact that they have an unparalleled pentagonal symmetry, which makes the atomic arrangement extremely ordered but not periodic. This unique feature offers them exclusive properties, such as resistance to heat, high stability, and low friction.
They were discovered just three decades ago; since then, researchers worldwide have been attempting to comprehend the properties of quasicrystals, in an attempt to make more progress in materials research. However, this is not easy, as quasicrystals are not commonly found in nature. Fortunately, they have been able to utilize structures similar to quasicrystals, known as “Tsai-type approximants.”
Complete knowledge about these structures could offer insights into the varied properties of quasicrystals. One such property is antiferromagnetism, wherein magnetic moments are aligned in a quasiperiodic order, unusually different from traditional antiferromagnets. Thus far, this property has never been noticed in quasicrystals but the probability was thrilling for materials scientists, as it could be an opening to an extensive range of new applications.
In a new research paper published in Physical Review B: Rapid Communications, scientists from the Tokyo University of Science, headed by Prof. Ryuji Tamura, discovered for the first time that a kind of Tsai-type approximant displays an antiferromagnetic transition.
This was a sensational finding, as it advocated that even quasicrystals could exhibit such a transition. The researchers were already aware that Tsai-type approximants have two types of variants: 1/1 and 2/1 approximants.
The key difference between the two is that 2/1 approximants have an extra rhombohedral unit in their structure, which is not present in the 1/1 type, making them even more well-ordered and closer to the structure of quasicrystals.
This is why the researchers were keen on seeing the conditions in which 2/1 approximants could exhibit antiferromagnetism; it created a likelihood of witnessing this new property even in quasicrystals.
Antiferromagnetic transitions have been observed in 1/1 approximants, but we observed it in a 2/1 approximant for the first time. This is interesting because unlike the 1/1 approximant, the 2/1 approximant contains all the components necessary to construct a quasicrystal.
Ryuji Tamura, Professor, Tokyo University of Science
To study the magnetic properties of 2/1 approximants closer, the researchers synthesized metallic alloys with a crystalline structure, which had both 1/1 and 2/1 approximants. They used a device known as the superconducting quantum interference device (SQUID) to explore the conditions under which the approximants exhibited different magnetic properties.
Fascinatingly, it was found that a single parameter governs the presence of antiferromagnetism in both types of approximants. This was the ratio of electron per atom, which somewhat differed in the two types. By controlling the electron-per-atom ratio, Prof. Tamura and his team observed a “transition” to an antiferromagnetic state in the two types of approximants.
This property had been witnessed in the 1/1 type before but not in the 2/1 approximant. This was a stimulating development, as the extremely ordered structure of the 2/1 approximant meant that it could be utilized to produce quasicrystals, making this the very first research to demonstrate the probability of antiferromagnetic quasicrystals.
We succeeded in observing, for the first time, antiferromagnetic transitions in the 1/1 and 2/1 AFM approximants in the same alloy system. Our finding clearly shows that the antiferromagnetic order survives in the 2/1 higher-order approximant, which has all the building blocks for creating a quasicrystal.
Ryuji Tamura, Professor, Tokyo University of Science
The importance of quasicrystals―for example, in regular applications like making needles for surgery and acupuncture, as well as frying pans―is well-established. However, given their latest discovery, not much has been understood about why they are so exceptional.
By demonstrating the presence of antiferromagnetism in a quasicrystal-like structure, Prof. Tamura and his team have potentially opened the door for greater advancements in quasicrystal research.
Antiferromagnetic quasicrystals had never been seen before, and this discovery has a great academic impact. The possibility of the existence of antiferromagnetic quasicrystals is a big step towards deciphering the mystery of quasicrystals.
Ryuji Tamura, Professor, Tokyo University of Science