Chemically Controlled Magnetic Material

Magnets are common in physics classes at school, but almost no chemistry classes are involved; researchers have successfully used chemical methods to control the magnetic properties of ferromagnetic substrates. Physical methods may affect the direction of the magnetic field. The chemical method in this example finely controls the selected ferromagnetic material system and works like a lithium-ion battery.

By entering lithium ions into specific magnets and deintercalating, their magnetic properties can be finely controlled. (Source: KIT/ Wiley-VCH)

Chemically Controlled Magnetic Material

Chemically Controlled Magnetic Material

Magnets are common in physics classes in schools, but almost no chemistry classes are involved; researchers at the Karlsruhe University of Technology (KIT) have successfully used chemical methods to control the magnetic properties of ferromagnetic substrates. Physical methods may affect the direction of the magnetic field. The chemical method in this example finely controls the selected ferromagnetic material system and works like a lithium-ion battery.

Many physical methods can reversibly create or affect magnetism. The standard method is to use a solenoid coil to generate a magnetic field with high current, but the coil continuously consumes energy. Another possible method is to polarize ferromagnets, meaning that the magnetized structures are arranged in parallel, affecting the magnetic field of the matrix. Although energy is not required to maintain the magnetic field, the magnetic properties are permanent and are not easily removed. Another method is to use electromagnetic coupling to induce magnetism using an electric field; however, the effect of this method is often limited to the top single-layer atomic lattice, causing minimal changes in magnetization.

KIT’s newly developed magnetic chemical control method proposes a unique approach that differs from the concept explained above: this method affects the matrix material, not only on the surface, but also reversible, which means it can be removed. Different magnetic states (magnetic or non-magnetic) are stable, which is innovative. Unlike electromagnetic coils, different magnetic states can be maintained without continuous current and no energy consumption.

“Thousands of charge and discharge cycles in mobile phone lithium-ion batteries show a highly reversible electrochemical process. This leads us to explore structures similar to lithium-ion batteries,” said Subho Dasgupta, KIT Nanotechnology Research Institute. During charging and discharging of a lithium ion battery, ions are transferred from one electrode to the other and into the electrode.

A team of scientists working with Dasgupta prepared a lithium-ion battery, one of which was made of maghemite, ferromagnetic iron oxide (γ-Fe2O3), and the other electrode made of pure metal lithium. Experiments have shown that lithium ion entering ferromagnetic hematite reduces the magnetization at room temperature. The magnetization of maghemite can be controlled by fine control of lithium ions, that is, by charging and discharging the battery. Similar to traditional lithium ion batteries, this effect can be cycled.

In the reported experiments, the researchers made a change in magnetization of 30%. In the long run, complete magnetic switch control is the goal. Scientists hope to find the same magnetic switch production process as the electric transistor: the electric transistor controls the current switch, and the magnetic switch controls the switch of the strong ferromagnet.

In principle, this method may replace any low-frequency electromagnet application, but in this case higher energy efficiency can be achieved. KIT scientists’ research focuses on small magnetic actuators for robots or microfluidics.

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