SPIN

Call for Papers

Guest Editors:
Qihang Liu (Southern University of Science and Technology, China)
Zheng Han (Shanxi University, China)
Jianpeng Liu (ShanghaiTech University, China)

Tentative timeline:
i. Submission deadline: May 2025
ii. Final notification of acceptance: September 2025
iii. Publication: December 2025

Introduction:
Magnetism, known as a quantum phenomenon in modern physics, has been documented since early history, and has long played an indispensable role in the advancement of human civilization. Throughout the 21st century, the understanding of magnetism has undergone four significant periods: comprehension of its fundamental nature, knowledge expansion into high-frequency regimes, large-scale industrial applications, and the most recent advent of spintronics. Historically, ferromagnetic materials have dominated magnetic applications due to their non-zero magnetization, which can couple with external magnetic fields, serving as an order parameter. On the other hand, antiferromagnetic materials, which manifest a symmetry-protected magnetic order with zero net magnetization characterized by alternating atomic magnetic moments, have also garnered significant interest. In recent years, the development of antiferromagnetic spintronics has sparked interest in magnetic materials with diverse magnetic structures. Particularly intriguing is a broad class of "unconventional magnets," which exhibit antiferromagnetic configurations while also displaying ferromagnetic-like properties. Unlike traditional antiferromagnets, unconventional magnets are expected to combine the advantages of both ferromagnetic and antiferromagnetic materials, offering figure-of-merits with high storage capacity, low power consumption, capability in electrical control and/or readout, and so on. These attributes hold great promise for the next-generation spintronic devices.

A predominant example of unconventional magnets is a recently predicted class of antiferromagnets characterized by momentum-dependent spin splitting. These materials lack a macroscopic net magnetic moment but exhibit various novel transport phenomena independent of spin-orbit coupling, including spin-polarized currents, spin-neutral currents, magnetoelectric effects, and the spin Hall effect. In 2022, the collinear antiferromagnets with momentum-dependent spin splitting were termed "altermagnets". Due to their simple magnetic structure and spin-polarized Fermi surfaces, these materials have then quickly become a focal point of research in the field of spintronics.

Another type of new magnetic states which have aroused significant research interest recently are the orbital magnetic states. In an ideal orbital magnet, the magnetization is contributed by the orbital angular momenta of charge carriers, which can be approximately decoupled from the spin degrees of freedom. This implies that the electrons may stay in a ground state that forms spontaneous current loops in real space. Recently, such orbital magnetic states have been experimentally realized in two-dimensional moiré superlattices and heterostructures. Some hints of spontaneous time-reversal symmetry breaking with non-vanishing orbital magnetic flux have also been observed in correlated Kagome lattice systems.

In particular, in two-dimensional moiré superlattices, low-energy electrons emerging from energy valleys of the constituent materials are coupled with some long-wavelength potential arising from the moiré lattice structure, which may significantly reduce the kinetic energy and even endow nontrivial topological properties to the electrons. As a result, these systems may enter orbital magnetic states due to spontaneous time-reversal symmetry breaking driven by electron-electron interactions, with the magnetization mostly contributed by orbital angular momenta, characterized by peculiar ground-state current pattern on the moiré length scale. Such orbital magnetic states have been experimentally realized in various moiré superlattices such as magic-angle twisted bilayer graphene, twisted multilayer graphene etc. Studies on the unique properties associated with these orbital magnetic states, such as the transport properties, collective excitations, phase-transition behaviors, optical properties, magnetoelectric couplings, phonon effects etc., are still in early stage. The potential applications to next-generation electronic and spintronic devices using such orbital magnets are also open questions.

This special issue aims to collect the latest studies focusing on the broad topic of “unconventional magnets” and “orbital magnets” from all different aspects, including theoretical modeling, synthesis, characterization, transport measurements, spectroscopy measurements, device applications, etc.

Topics for this special issue include (but are not limited to):
i) Spin-split antiferromagnets and altermagnets
ii) Anomalous Hall antiferromagnets
iii) Topological magnets
iv) Orbital magnetism and topological states in moiré lattices
v) Time-reversal breaking effects in Kagome lattices