Berkeley Lab reports on electric field switching of ferromagnetism at room temp
In a development that holds promise for future magnetic memory and logic devices, researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and Cornell University successfully used an electric field to reverse the magnetization direction in a multiferroic spintronic device at room temperature. This demonstration, which runs counter to conventional scientific wisdom, points a new way towards spintronics and smaller, faster and cheaper ways of storing and processing data.
This is a conceptual illustration of how magnetism is reversed (see compass) by the application of an electric field (blue dots) applied across gold capacitors. Blurring of compass needle under electric field represents two-step process.
Credit: (Image courtesy of John Heron, Cornell)
"Our work shows that 180-degree magnetization switching in the multiferroic bismuth ferrite can be achieved at room temperature with an external electric field when the kinetics of the switching involves a two-step process," says Ramamoorthy Ramesh, Berkeley Lab's Associate Laboratory Director for Energy Technologies, who led this research. "We exploited this multi-step switching process to demonstrate energy-efficient control of a spintronic device."
Ramesh, who also holds the Purnendu Chatterjee Endowed Chair in Energy Technologies at the University of California (UC) Berkeley, is the senior author of a paper describing this research in Nature. The paper is titled "Deterministic switching of ferromagnetism at room temperature using an electric field." John Heron, now with Cornell University, is the lead and corresponding author. (See below for full list of co-authors).
Multiferroics are materials in which unique combinations of electric and magnetic properties can simultaneously coexist. They are viewed as potential cornerstones in future data storage and processing devices because their magnetism can be controlled by an electric field rather than an electric current, a distinct advantage as Heron explains.
"The electrical currents that today's memory and logic devices rely on to generate a magnetic field are the primary source of power consumption and heating in these devices," he says. "This has triggered significant interest in multiferroics for their potential to reduce energy consumption while also adding functionality to devices."
Nature, however, has imposed thermodynamic barriers and material symmetry constrains that theorists believed would prevent the reversal of magnetization in a multiferroic by an applied electric field. Earlier work by Ramesh and his group with bismuth ferrite, the only known thermodynamically stable room-temperature multiferroic, in which an electric field was used as on/off switch for magnetism, suggested that the kinetics of the switching process might be a way to overcome these barriers, something not considered in prior theoretical work.
"Having made devices and done on/off switching with in-plane electric fields in the past, it was a natural extension to study what happens when an out-of-plane electric field is applied," Ramesh says.
Ramesh, Heron and their co-authors set up a theoretical study in which an out-of-plane electric field - meaning it ran perpendicular to the orientation of the sample - was applied to bismuth ferrite films. They discovered a two-step switching process that relies on ferroelectric polarization and the rotation of the oxygen octahedral.
"The two-step switching process is key as it allows the octahedral rotation to couple to the polarization," Heron says. "The oxygen octahedral rotation is also critical because it is the mechanism responsible for the ferromagnetism in bismuth ferrite. Rotation of the oxygen octahedral also allows us to couple bismuth ferrite to a good ferromagnet such as cobalt-iron for use in a spintronic device."
To demonstrate the potential technological applicability of their technique, Ramesh, Heron and their co-authors used heterostructures of bismuth ferrite and cobalt iron to fabricate a spin-valve, a spintronic device consisting of a non-magnetic material sandwiched between two ferromagnets whose electrical resistance can be readily changed. X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) images showed a clear correlation between magnetization switching and the switching from high-to-low electrical resistance in the spin-valve. The XMCD-PEEM measurements were completed at PEEM-3, an aberration corrected photoemission electron microscope at beamline 11.0.1 of Berkeley Lab's Advanced Light Source.
"We also demonstrated that using an out-of-plane electric field to control the spin-valve consumed energy at a rate of about one order of magnitude lower than switching the device using a spin-polarized current," Ramesh says.
In addition to Ramesh and Heron, other co-authors of the Nature paper were James Bosse, Qing He, Ya Gao, Morgan Trassin, Linghan Ye, James Clarkson, Chen Wang, Jian Liu, Sayeef Salahuddin, Dan Ralph, Darrell Schlom, Jorge Iniguez and Bryan Huey.
Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.lbl.gov.
DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov.
Lynn Yarris | EurekAlert!
Tangled magnetic fields power cosmic particle accelerators
14.12.2018 | DOE/SLAC National Accelerator Laboratory
In search of missing worlds, Hubble finds a fast evaporating exoplanet
14.12.2018 | NASA/Goddard Space Flight Center
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy