Large industries such as modern microelectronics are based on the interaction between matter and electromagnetism. Electromagnetic signals can be processed and stored in specially adapted materials. In materials science, electrical and magnetic effects have generally been studied separately. However, there are extraordinary materials called “multiferroic”, in which the electric and magnetic excitations are closely linked. Scientists from the Vienna University of Technology (TU Wien) have now shown in an experiment that magnetic properties and excitations can be influenced by electrical voltage. This opens up completely new possibilities for high-frequency electronics.
The best of both worlds
It has long been well known that electricity and magnetism are two sides of the same coin. Waves in free space, such as visible light or cell phone radiation, always consist of both an electric and a magnetic component. When it comes to the properties of materials, however, electricity and magnetism have been considered separate topics. There are magnetically operated materials, which react to magnetic fields, and there are electrically operated materials, which can be influenced by electric fields.
A magnet has a magnetic field, but no electric field. In a piezoelectric crystal, on the other hand, electric fields can be generated, but not magnetic fields. Having both at the same time seemed impossible. “Usually the two effects are created very differently,” says Prof. Andrei Pimenov (TU Vienna). “Magnetic order comes from electrons aligning their magnetic moments, electrical order comes from positive and negative charges moving relative to each other.”
In 2006, Andrei Pimenov (while working at the University of Augsburg) found evidence of excitations based on both electric and magnetic order. These excitations, which have been dubbed “electromagnons”, have since been hotly debated by materials scientists. Pimenov and his team succeeded in turning such excitations on and off with an electric field in a special material composed of dysprosium, manganese and oxygen (DyMnO3).
In this material, many electrons align their magnetic moments at low temperature. Each electron has a magnetic direction that is slightly distorted relative to the adjacent electron – hence the electrons create a spiral of magnetic moments. The spiral has two possible orientations – clockwise or counter-clockwise – and, surprisingly, an external electric field can switch between these two possibilities.
Vibrating atoms, flickering moments
In magnetoelectric materials, the magnetic charges and moments of atoms are linked. In dysprosium manganese oxide, this connection is particularly strong: “When the magnetic moments waver, the electric charges also move”, explains Andrei Pimenov. In this material, magnetic moments and electric charges simultaneously play a role in excitation, and therefore both can be influenced by a single external field.
The effect can be demonstrated by sending terahertz radiation through the material: the polarization of the terahertz beam is changed if the multiferroic material exhibits magnetic order. If the magnetic spiral in the material can be switched with an electric field, that electric field eventually determines whether the polarization of the terahertz beam is rotating.
Ideas for future applications are numerous: Wherever it is desirable to combine the respective advantages of magnetic and electric effects, new magneto-electric materials could be used in the future. This could lead to new types of amplifiers, transistors or data storage devices. In addition, very sensitive sensors could be built with electromagnetic technology.
Inversion of the magnetic moment by an electrical voltage in a single material could lead to new low-power electronic devices
Shuvaev et al., Phys. Rev. Lett. 111, 227201 (2013)
Provided by Vienna University of Technology
Quote: The ‘Electromagnon’ effect couples electricity and magnetism in materials (27 November 2013) retrieved 1 March 2022 from https://phys.org/news/2013-11-electromagnon-effect-couples-electricity- magnetism.html
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