Antiferromagnets are at the center of the project DIMAF as very promising candidates for the development of efficient new technologies with a low power consumption. However, this has not always been the case, they have long been considered as "extremely interesting from the theoretical viewpoint, but do not seem to have any applications", even by Louis Néel himself in his Nobel lecture in 1970.

Antiferromagnets are indeed very difficult to measure and to manipulation for a simple reason: they do not have a net magnetization. In a ferromagnet, a usual magnet, the magnetization of every atom is pointing in the same direction which leads to the presence of a global magnetization which produces a magnetic stray field and reacts to an external magnetic field. In the case of antiferromagnets, the magnetization direction is opposite for neighbouring atoms and fully compensated at the macroscopic scale. And then, there is no magnetic stray field and almost no effect when we apply an external field!

Nevertheless, they are already in use, in particular in reading heads of hard drives because of the interesting coupling appearing at the interface between a ferromagnet and an antiferromagnet. The objective is to go further and profit from the properties which make them so promising:

  • They are robust to the presence of external fields and do not produce parasitic fields.
  • Their local magnetization can be manipulated much faster than the one of ferromagnets at THz rather than GHz frequencies.
  • Theoretically, they can be manipulated in a way that consumes a very low power.

In order to be able to study them, we still need a simple method to image their magnetic state. It remains a challenge because of the lack of net magnetization but several technique are emerging to tackle this issue. In particular, NV center magnetometry is the one which we use in the project DIMAF. The antiferromagnets we investigate are presented below.

Bismuth ferrite

Bismuth ferrite is the material which me mainly investigate in the project because it exhibits a strong coupling between the magnetic order and the electric polarization at room temperature. This allows the control of magnetism with electric field, a crucial point in the development of devices with a low power consumption.

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Synthetic antiferromagnets

Synthetic antiferromagnets are magnetic stacks containing layers with opposite magnetization. They are highly tunable through the choice of the layers'thicknesses and composition, which allow the optimization of their properties for specific applications.

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