Magnets are well known in school physics lessons, but they are hardly discussed in chemistry lessons; and it is still a chemical process by means of which researchers at the Karlsruhe Institute of Technology (KIT) have succeeded in controlling the magnetic properties of bulk ferro-magnets. While physical processes can influence the orientation of magnetic fields, the chemical process in this case controls magnetism in carefully chosen systems of strongly ferromagnetic materials. The principle of operation used in this case is similar to the concept of lithium-ion batteries.
There are several possibilities for creating or influencing magnetism reversibly, by physical means. Standard methods are to either use an electromagnetic coil, for example, where a high current produces a magnetic field, but the coil constantly consumes energy. Another possibility is to polarize the ferromagnetic, i.e. to align the magnetic structures in the material in parallel, so that an overall magnetic field is generated. No energy is required to maintain this magnetic field, but it is permanent and cannot be easily removed. Another option is magnetoelectric coupling, where an electric field is used to induce magnetism; however, this mechanism is often limited to the upper monolayer of atoms of the crystal lattice only. Therefore, minimal change in magnetization results.
The newly developed chemical magnetism control at KIT offers a unique approach that goes beyond the concepts explained above: the process influences the bulk material, not just the surface, and it is reversible, which means it can to be undone. The separate magnetic states (magnetic / non-magnetic) are non-volatile, which offers the major novelty that the different magnetic states – unlike the electromagnetic coil – can be maintained without requiring a continuous flow of current and consumption of energy.
âThousands of charge-discharge cycles of lithium-ion batteries used in cell phones, for example, show that electrochemical processes can be highly reversible. This led us to the idea of ââexploiting similar structures such as lithium-ion batteries, âexplains Subho. Dasgupta from the KIT Nanotechnology Institute. During the charging and discharging of a lithium-ion accumulator, the ions migrate from one electrode to another and become intercalated in the electrode.
The team of scientists working with Dasgupta have now produced a lithium-ion battery, in which an electrode is made of maghemite, a ferromagnetic iron oxide (Î³-Fe2O3), and the other electrode is made of pure lithium metal. Experiments have revealed that the intercalation of lithium ions in maghemite reduces its magnetization at room temperature. By the specific control of lithium ions, that is to say by charging and discharging the accumulator, the magnetization of the maghemite can be controlled. Similar to conventional lithium-ion batteries, this effect can be repeated.
In the reported experiments, the researchers achieved a variation in magnetization of up to 30%. In the long term, the goal is to achieve full on / off magnetic switching. Scientists hope to find a method to produce a magnetic switch that works on the same principle as an electric transistor: while the latter turns a controlled current on and off, the magnetic switch turns a powerful ferromagnetic on and off. .
In principle, this process can replace all applications where low frequency electromagnets are used, but in this case it can achieve much higher energy efficiency. The research of KIT scientists mainly focuses on small magnetic actuators for use in (micro) robots or microfluidics.
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