Pulsed Magnet Experiment: Gaulin and Nojiri
Hiroyuki Nojiri, Institute for Materials Research, Tohoku Univeristy, Department of Physics.
A team of scientists has completed a pioneering set of experiments using a 30 Tesla pulsed magnet to subject a material sample to extremely high magnetic fields at the Spallation Neutron Source.
Professor Hiroyuki Nojiri of Tohoku University in Sendai, Japan, developed the new pulsed magnet technique, shattering previous field strength limits for neutron science. SNS is the first American neutron scattering facility to collaborate with Nojiri and construct a prototype system.
A user team led by Nojiri and Bruce Gaulin of McMaster University in Hamilton, Ontario, Canada, in collaboration with Lou Santodonato and Garrett Granroth of SNS, were the first researchers to use the new sample environment. Their experiment tested a sample of manganese tungstate on the SEQUOIA spectrometer, especially designed for the study of novel materials and operated in a Laue diffraction mode. The team zapped a sample with a 30 T field, the goal for their experiments.
The research team wasn’t even sure its experiments would produce results, Gaulin said, so just knowing the setup was working was a triumph. “We were looking to measure a diffraction pattern and how it changes with a magnetic field. The team saw different diffraction patterns emerging as the material moved from phase to phase as the magnetic field intensified. We knew the magnetic field was actually getting that high, that we were getting the sample to feel the magnetic field in such a short time.”
Left to right: Sasha Kolesnikov, SEQUOIA instrument scientist; Hiroyuki Nojiri, Institute for Materials Research, Tohoku University; and Bruce Gaulin, McMaster University, Department of Physics and Astronomy.
The team actually collected results at several different magnetic powers. Experiments were conducted at 7, 15, and 24 T during the first day and then at 30 T the second day.
Manganese tungstate exhibits a complicated array of phrases at extremely low temperatures, some of which are multiferroic, or magnetically and electrically ordered at the same time, said Gaulin. “These materials offer the potential for controlling the magnetism by applying an electrical field and controlling the polarization by applying a magnetic field. They could be very interesting from the standpoint of developing devices, such as memory storage.” The study of multiferroics as such is a relatively new field, about 5 years old, Gaulin noted. “The materials have been around for a while, but people had been studying them either for their magnetic or electrical properties; only recently have we started studying the two together.”
The team’s goal is to help reveal the underlying physics of the material, with a view toward equipping materials scientists with the understanding needed to scale up the temperatures at which multiferroics can operate so they will be technologically useful. “For now, it’s a basic science problem, curiosity driven. But people are imagining applications already,” Gaulin said.
Left to right: Lou Santodonato, Garrett Granroth, Hioyuki Nojiri, Jeremy Carlo, Kyoko Okada, Motoyoshi Yasui, Bruce Gaulin, Kate Ross, and Masaaki Matsuda.
When a sample of the material is taken to an extremely low temperature and then perturbed with a magnetic field, it typically changes magnetic phases. As it does so, the experimenters can study the behaviors associated with the phases. The larger the magnetic field applied, the more phase behaviors can be studied. “All this is telling you details about what underlies the magnetism in the material and its interesting properties,” Gaulin said.
Sorting out the different sets of results from the experiments—the energy of the neutrons, the patterns at different magnetic field strengths—will be challenging, Gaulin noted. The researchers will have to work closely with the data acquisition and data analysis teams at SNS to understand their data.
The difficulty of the task underscores the importance of having SNS available, he added. “It’s an ambitious experiment in several directions at once: pushing the source, pushing the sample environment, the data acquisition system. Doing this at any other neutron source would be very difficult. What you would like to do, in principle, is measure the diffraction pattern with one pulse or a small number of pulses. Being at the most powerful source pays a big dividend.”
The pulsed magnet setup represents the state of the art in sample environments, he said. “This is the ultimate of what the sample environment team does.”
