Antiferromagnetic Materials: Properties and Applications

Antiferromagnetic materials are a type of material that exhibit antiferromagnetic order, a state where the magnetic moments of the constituent atoms or ions are aligned in an antiparallel manner. These materials have recently gained renewed interest due to their potential use in spintronics technologies, where spin transport is the foundation of their functionalities. Antiferromagnetic materials can be classified into two main categories: insulating and conducting.

Insulating antiferromagnets, which are mostly oxides such as NiO and halides such as MnF, have been well-studied recently due to their potential to carry chargeless spin waves (magnons). Conducting antiferromagnets, on the other hand, have non-collinear chiral or non-coplanar spin structures, which do not have easy corresponding systems in typical ferromagnets.

The study of antiferromagnetic materials has been motivated by several factors. Firstly, antiferromagnetic order is more robust to moderate external magnetic fields compared to ferromagnetic order. Secondly, antiferromagnetic materials have zero net magnetization, which does not produce stray fields, and switching timescales that correspond to switching rates in the THz regime. Thirdly, the precession frequency of antiferromagnetic order is set by the geometric mean of the anisotropy and exchange energies, leading to antiferromagnetic switching that is up to two orders of magnitude faster than ferromagnetic switching.

In recent years, research on antiferromagnets has been motivated by the potential to manipulate and read antiferromagnetic order using spin–orbit-torques generated by charge currents, staggered local relativistic fields induced by electrical currents, domain wall motion, and optical excitation by circularly polarized light. However, many aspects regarding manipulation of antiferromagnetic order are still unknown, including the influence of thermal effects, the timescale of antiferromagnetic switching and manipulation, and even the mechanism and robustness of the switching itself.

Apart from their potential use in spintronics, antiferromagnetic materials also have applications in other fields. For example, researchers have studied the anisotropy independence and electrical manipulation of antiferromagnetic materials like CoO and NiO, as well as their suitability for future data storage applications. Additionally, anomalous Hall antiferromagnets, which generate a non-zero Hall effect, have been identified and studied, as they contribute to the emerging field of multipole magnetism, topological condensed matter, and spintronics.

In summary, antiferromagnetic materials are a fascinating and versatile class of materials with a rich physics that offers potential for various applications, including spintronics and data storage. However, further experimental and theoretical study is needed to fully understand and harness their properties.