Argonne scientists find new "multiferroic" material

 

	Argonne scientist John Mitchell assembles the high pressure furnace used in creating the multiferroic properities of FeTi03.

The trail to a new multiferroic material started with the theories of a U.S. Department of Energy's (DOE) Argonne National Laboratory scientist and ended with a multidisciplinary collaboration that created a material with potential impact on next generation electronics. 

Argonne scientist Craig Fennie's principles of microscopic materials design predicted that the high pressure form of FeTiO₃ would have both weak ferromagnetism and ferroelectric polarization, an unusual combination in a single material. 

"We were able to take the theory and, through targeted synthesis and measurement, prove that FeTiO₃ has both weak ferromagnetism and ferroelectricity, just as Craig predicted," Argonne scientist John Mitchell said. "Success in this materials design and discovery project would not have been possible without a collaborative team involving several disciplines and talents from across the lab and indeed the country."

Scientists from Argonne's materials science division and Center for Nanoscale Materials along with scientists from Pennsylvania State University, University of Chicago and Cornell University used piezoresponse force microscopy, optical second harmonic generation and magnetometry to show ferroelectricity at and below room temperature and weak ferromagnetism below 120 Kelvin for polycrystalline FeTiO3 synthesized at high pressure.

Multiferroic materials show both magnetism and polar order, which are seemingly contradictory properties. Magnetic ferroelectrics may have applications in memory, sensors, actuators and other multifunctional devices by acting as magnetic switches when their electric fields are reversed.

This project was recently published in Physical Review Letters and will be featured in the upcoming Advanced Photon Source annual report.

Funding for this research was provided by the U.S. Department of Energy, Office of Science.

Chromium's secrets revealed at Argonne's Advanced Photon Source

	University of Chicago scientist Rafael Jaramillo and Argonne scientist Yejun Feng examine the element chromium at the Advanced Photon Source. Studying simple metallic chromium, the joint UC-Argonne team has discovered a pressure-driven quantum critical regime and has achieved the first direct measurement of a "naked" quantum singularity in an elemental magnet.

Scientists at the U.S. Department of Energy's Argonne National Laboratory and the University of Chicago have reached a milestone in the study of emergent magnetism.

Studying simple metallic chromium, the joint UC-Argonne team has discovered a pressure-driven quantum critical regime and has achieved the first direct measurement of a "naked" quantum singularity in an elemental magnet.  The team was led by University of Chicago scientist Rafael Jaramillo, working in the group of Thomas Rosenbaum, and Argonne scientist Yejun Feng of the Advanced Photon Source.

The sophisticated spin and charge order in chromium is often used as a stand-in for understanding similar phenomena in more complex materials, such as correlated oxides proximate to a quantum critical point.

"Chromium is a simple metallic crystal that exhibits a sophisticated form of antiferromagnetism," said Jaramillo.  "The goal was to find a simple system."

Quantum criticality describes a continuous phase transition that is driven by quantum mechanical fluctuations, and is thought to underlie several enigmatic problems in condensed matter physics including high-temperature superconductivity.  However, achieving a continuous quantum phase transition in a simple magnet has proved to be a challenging goal, as the critical behavior in all systems studied to date has been obscured by competing phenomena.  The discovery of a "naked" transition in simple chromium metal therefore paves the way for a more detailed understanding of magnetic quantum criticality.

Like many elements, chromium has been extensively studied for decades and a discovery of this magnitude in a well-known element is particularly important.

"It's not often that you find out something new in a conventional element," Feng said.

The pressure scale and experimental techniques required to measure quantum criticality in chromium necessitated extensive technical development at both Argonne and the University of Chicago. The resulting techniques for high precision measurement of condensed matter systems at high pressure, developed for use at Sector 4 of the Advanced Photon Source, now approach a level of precision and control comparable to more conventional techniques such as magnetic varying field and temperature.

This work is reported in the May 21 issue of the journal Nature.

Funding for this research was provided by the National Science Foundation Division of Materials Research and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Argonne scientists find new "multiferroic" material