A four-stroke engine for atoms

You can restore the original state by switching a bit of memory on a computer.

A four-stroke engine for atoms

You can restore the original state by switching a bit of memory on a computer. Only two states can be called "0" and "1".

TU Wien (Vienna), however, has discovered an incredible effect: An atomic switch that must be switched back and forth twice to reach the original state was found in a crystal based upon oxides of manganese and gadolinium. The spin of gadolinium-atoms makes one complete rotation during this double switching-on/off process. This is similar to a crankshaft where an up-and down movement is transformed into a circular motion.

This phenomenon opens up new possibilities in material physics. These systems could even store information. Nature now presents the strange atomic switch.

Combination of magnetic and electrical properties

The electrical and magnetic properties are usually distinguished. The fact that charge carriers move is what gives rise to electrical properties. For example, electrons traveling through metals or ions that have their position shifted.

Magnetic properties are, however, closely related to the spin and angular momentum of atoms. This can be in the same direction that the Earth's axis points in, or in a very particular direction.

There are materials, however, in which the magnetic and electrical phenomena are closely related. These materials are being studied by Prof. Andrei Pimenov, and his team from the Institute of Solid State Physics of the TU Wien. Andrei Pimenov says, "We exposed a special gadolinium, oxygen and manganese material to a magnet field and measured its electrical polarization changes in the process." "We wanted to see how magnetism can alter the material's electrical properties. Surprisingly, we discovered a completely unexpected behavior.

Four steps to get back to the beginning

The material's electrically polarization is the first thing you notice. On one side, it is positively charged and on the opposite side, it is negatively charged. You can then switch on a strong magnet field and the polarization will change very little. But if you switch off the magnetic field again, a dramatic shift occurs: suddenly, the polarization changes: the side that was previously positively charged is now negatively charged and vice versa.

You can repeat the process again: Simply switch on the magnet field, and the electric polarization will remain approximately constant. The polarization reverses if you turn off the magnetic field. It then returns to its original state.

Andrei Pimenov says, "This is a remarkable feat." "We go through four steps. Each time the material changes its internal property, the polarization changes only twice. So, you only reach the initial state after the fourth step.

Four-stroke engine for gadolinium

This behavior is caused by the gadolinium-atoms. They alter their spin direction at each step, changing it by 90 degrees each time. Andrei Pimenov says that it is a four-stroke engine designed for atoms. It takes four steps to return to the initial state in a four-stroke engine. The cylinder also moves twice as fast. The magnetic field is able to move up and down twice in our case before the initial state can be restored. Once that happens, the spin of the gadolinium-atoms will point back in the original direction.

These materials could theoretically be used to store information. A system with four possible states would have two bits of storage per switch instead of the normal one bit for "0" and "1. This effect is particularly relevant for sensor technology. One could create a counter for magnet pulses using this method. This effect is an important input for theoretical research. It is also another example of a "topological effect", a class that has been at the forefront of solid-state physics for many years. This effect should allow for the development of new materials.

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