Nav: Home

Frustrated materials under high pressure

April 24, 2019

People are not the only ones to be occasionally frustrated. Some crystals also show frustrations. They do so whenever their elementary magnets, the magnetic spins, cannot align properly. Cesium copper chloride (Cs2CuCl4) - or CCC for short - is a prime example of frustrated materials. In this crystal, the magnetic copper atoms reside on a triangular lattice and seek to align themselves antiparallel to each other. In a triangle, this does not work, however. This geometric frustration challenges physicists. After all, it promises the discovery of new magnetic phenomena that may even be used for quantum computers in the future. To better investigate and understand the underlying basics, physicists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, supported by Japanese and American colleagues, can now control the magnetic coupling using an elegant measuring method.

"Our aim is to elucidate the complex quantum processes in geometrically frustrated crystals in detail," explains Dr. Sergei Zvyagin from the Dresden High Magnetic Field Laboratory at the HZDR. Theories about the magnetic behavior of crystals such as CCC abound. But so far, sophisticated experiments to test these theories on the object itself have been lacking. To this end, it is helpful to deliberately change the strength of the interactions between the magnetic atoms.

Physicists in many laboratories often take a tedious route: they produce crystals with geometric frustration in a slightly different chemical composition. This changes the magnetic interaction between the elementary magnets, but sometimes also - unintentionally - the crystal structure. Zvyagin left this laborious, purely chemical path to deeper knowledge. Instead, he used high pressures. Under these conditions, the strength of the coupling of the magnetic spins can be changed quasi-continuously.

"With the new method, we can control the coupling parameters within the crystal and simultaneously measure the effects on the magnetic properties," says Sergei Zvyagin. He received the CCC crystals for his experiments from Dr. Hidekazu Tanaka's group at the Tokyo Institute of Technology. With an edge length of just a few millimeters and their shimmering orange translucency, they are more reminiscent of bright garnet gemstones than of artificial crystals grown in the laboratory.

Also in Japan, at Tohoku University in Sendai, Zvyagin and his colleagues placed the crystals in a high-pressure press with pistons made of high-strength zirconium oxide. The researchers gradually increased the pressure to around two gigapascals - a pressure similar to the one exerted by the weight of a car on a surface the size of a colored pencil lead.

"Under this pressure, the distances between the atoms changed very little," says Zvyagin. "But the magnetic properties of the crystal showed a drastic change." The researchers were able to measure these changes directly using electron spin resonance (ESR). They determined the transmittance for light (or more precisely: microwaves) in a very strong external magnetic field of up to 25 Tesla - about half a million times stronger than the Earth's magnetic field. In addition, the crystal had to be deep-frozen to -271 degrees Celsius, almost to absolute zero, in order to avoid disturbing effects caused by heat.

These measurements in a strong external magnetic field revealed the very unusual magnetic properties of the material. The researchers were able to vary the strength of the coupling between neighboring magnetic spins by changing the pressure. Further measurements using an additional method from materials research - the tunnel diode oscillator (TDO) technique - complemented these results. The TDO measurements were carried out - also under high pressures and in strong magnetic fields - at the Florida State University in Tallahassee.

In addition, Zvyagin and his colleagues found evidence that CCC under high pressure exhibits a cascade of new phases with increasing magnetic field, absent at zero pressure. "Thanks to these measurements, we are now a step further towards better understanding the variety of these phases," says Professor Joachim Wosnitza, head of the Dresden High Magnetic Field Laboratory.

"The exact identification of these phases is one of our next targets," says Zvyagin. In the future, he intends to determine the exact structures of his CCC crystals by means of neutron scattering. For these plans, he appreciates the excellent research conditions offered by the HZDR with its close international network. "For me, it is an ideal place for my interest in fundamental research," says the physicist. "And if we understand the quantum processes in these crystals with frustrated geometry, applications could also emerge."

Joachim Wosnitza also sees great potential in the exotic magnetic properties of these crystals. "One could imagine long-lived quantum systems in which the magnetic spins can be used in a controlled manner," says Wosnitza. "Whether this will then lead to a quantum computer or a special sensor cannot yet be anticipated, however." The road to such applications could still be very long. But with their successful measurements, the HZDR researchers have no reason to be frustrated - unlike their crystal samples.
-end-


Helmholtz-Zentrum Dresden-Rossendorf

Related Magnetic Field Articles:

Earth's last magnetic field reversal took far longer than once thought
Every several hundred thousand years or so, Earth's magnetic field dramatically shifts and reverses its polarity.
A new rare metals alloy can change shape in the magnetic field
Scientists developed multifunctional metal alloys that emit and absorb heat at the same time and change their size and volume under the influence of a magnetic field.
Physicists studied the influence of magnetic field on thin film structures
A team of scientists from Immanuel Kant Baltic Federal University together with their colleagues from Russia, Japan, and Australia studied the influence of inhomogeneity of magnetic field applied during the fabrication process of thin-film structures made from nickel-iron and iridium-manganese alloys, on their properties.
'Magnetic topological insulator' makes its own magnetic field
A team of U.S. and Korean physicists has found the first evidence of a two-dimensional material that can become a magnetic topological insulator even when it is not placed in a magnetic field.
Scientists develop a new way to remotely measure Earth's magnetic field
By zapping a layer of meteor residue in the atmosphere with ground-based lasers, scientists in the US, Canada and Europe get a new view of Earth's magnetic field.
Magnetic field milestone
Physicists from the Institute for Solid State Physics at the University of Tokyo have generated the strongest controllable magnetic field ever produced.
New world record magnetic field
Scientists at the University of Tokyo have recorded the largest magnetic field ever generated indoors -- a whopping 1,200 tesla, as measured in the standard units of magnetic field strength.
Researchers discover link between magnetic field strength and temperature
Researchers recently discovered that the strength of the magnetic field required to elicit a particular quantum mechanical process corresponds to the temperature of the material.
Astronomers observe the magnetic field of the remains of supernova 1987A
For the first time, astronomers have directly observed the magnetism in one of astronomy's most studied objects: the remains of Supernova 1987A (SN 1987A), a dying star that appeared in our skies over thirty years ago.
Watch: Insects also migrate using the Earth's magnetic field
A major international study led by researchers from Lund University in Sweden has proven for the first time that certain nocturnally migrating insects can explore and navigate using the Earth's magnetic field.
More Magnetic Field News and Magnetic Field Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.