How do you align antiferromagnetic domains? A natural property if ferromagnets, like iron, is that they form magnetic domains with moments pointing in random orientations. However, one can align all of these domains by applying an external magnetic field. The closer you are to the Curie temperature, the smaller the magnetic field for aligned domains needs to be. This is all standard textbook phenomena and is essentially how fridge magnets are made.

For antiferromagnets, one also has domains with different orientations upon cooling below the Neel antiferromagnetic transition temperature. My question is, can antiferromagnetic domains of different orientations be aligned in a practical way like one does for ferromagnets?
For the sake of simplicity, let's assume everything is an ideal single crystal. Also, since the only practical and commonly available antiferromagnet I know of is nickel oxide, so let us assume the antiferromagnet is NiO.
Naively, I thought perhaps one can align the antiferromagnetic domains by just applying a very large magnetic field. But, unlike ferromagnets, applying a strong magnetic field in antiferromagnets causes a spin flop transition, where the opposite spins of the antiferromagnet face 90 degrees away from each other and 45 degrees away from the field (see image below). It's not clear that this would help with reducing domains at all.

 A: Surprisingly, it appears there is no simple and universal way to align antiferromagnetic domains, unlike in ferromagnets. In fact, it appears that Neel vector control of antiferromagnets is an active topic of research, with the recent thesis below discussing the topic in the context of certain intermetallic antimonides.
Control of Néel vector in Antiferromagnets by In Jun Park (UC Riverside Thesis, 2020)
Current efforts to align antiferromagnetic domains tend to work indirectly. Here are a few methods

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*E-Field: Applying electric fields to strain the crystal lattice, a certain preference will be given for spin orientation due to a change in the exchange energy between sites. A weakness of this method is that massive electric fields are usually needed to induce appreciable strain. Moreover, this method is ineffective for metallic antiferromagnets.


*Exchange-biasing: Another method for aligning AFM domains is exchange biasing, where a thin film of an antiferromagnet interacts with a thin film of a ferromagnet that can be controlled. Due to the interfacial exchange coupling, some degree of control over the antiferromagnet domains is possible. However, a great deal of interfacial engineering is needed, so this method requires a lot of luck with getting the right chemistry.


*Spin-torque: Yet another method is to use electric current to induce a spin-torque (see this article). This method uses the fact that flipping a spin on an electron results in a torque on the system. So by strategically injecting current into the system with the right initial spin direction, one can flip around AFM domains.
