An international research collaboration has uncovered some fascinating properties of the multiferroic material manganese-doped germanium telluride (Mn-doped GeTe), which holds promise for the future of energy-efficient computing.
Multiferroics are a unique class of materials that can be both magnetized and polarized at the same time, which means that they are sensitive to both magnetic and electric fields.
Having both these properties in a single material has made multiferroics very interesting for research and commercial purposes with potential applications from advanced electronics to next-generation memory storage. By understanding and harnessing the properties of these elements, researchers aim to develop more efficient, compact, and even energy-saving technologies.
In the case of Mn-doped GeTe, the “doped” part of the name simply means that a small amount of manganese atoms has been introduced into the germanium telluride crystal structure to modify its properties.
Mn-doped GeTe is known for its unique ferroelectric and magnetic properties. But the new study, which appeared in Nature Communications, has now found that it also possesses a magnetic order distinct from typical ferromagnets, such as iron, which align with a magnetic field. Instead, the scientists found that Mn-doped GeTe exhibits the characteristics of a ferrimagnet.
A ferrimagnet is like two magnets with slightly different strengths superimposed on top of each other. The discovery that Mn-doped GeTe behaves like this means that it allows for more flexibility to control the direction of magnetization—an essential feature for several technologies.
This proved to be important, as it allowed the scientists to develop a method for enhancing the efficiency of switching magnetization direction by an astounding six orders of magnitude.
Instead of doing this in the traditional way of applying a large current pulse to Mn-doped GeTe, they instead used a small, constantly fluctuating (AC) electrical current, followed by a tiny current nudge at just the right moment—a bit like pushing a swing at the right time to make it go higher with less effort. The researchers named this phenomenon “stochastic resonance.”
This tiny “nudge” caused a change that spread quickly throughout Mn-doped GeTe, like a ripple in a pond. This happened because the material behaves a bit like a solid and a bit like a liquid—essentially a glass: a change in one part causes a chain reaction that changes other parts.
In other words, the magnetic switch propagated swiftly across the Mn-doped GeTe through collective excitations, which are coordinated collective movements of a large number of electron spins within the material.
“This is possible because the system forms a correlated spin glass, where the local magnetic moments are in a glassy state, similar to atoms in an old-fashioned window,” Hugo Dil, co-author of the study, said in a media statement. “If one spin is forced to change its orientation, this information will travel like a wave through the sample and cause the other magnetic moments to also switch.”
According to Dil, for technological applications, this increase in switching efficiency is very interesting.
“It can eventually lead to computers that need less than one-millionth of the currently required energy to switch a bit. However, as a physicist, what really intrigues me is the collective behaviour. We are now planning space- and time-resolved experiments to follow how these excitations spread and how we can control them,” he said.
