Year: 2025
Type: article
Abstract: Antiferromagnets have garnered significant attention due to their unique magnetic properties and promising application prospects in the fields of information storage, spintronics, and quantum computing. Unlike ferromagnetic materials, where the magnetic moments of adjacent atoms align parallel, antiferromagnetic materials exhibit an antiparallel alignment of adjacent spins. This results in a net magnetic moment of zero in an ideal case and a property that eliminates stray magnetic fields, offering advantages for high-density magnetic storage and spintronic devices. However, the lack of a nonzero net magnetic moment also makes the detecting and characterizing of the antiferromagnetic order exceptionally challenging using conventional techniques. The search for effective methods to probe the intricate properties of antiferromagnetic materials has thus become a critical topic of modern physics. Optical second harmonic generation (SHG) has emerged as a powerful tool for characterizing antiferromagnetic materials. As a nonlinear optical process, SHG involves two photons combining into one with twice the photon frequency, which is a phenomenon sensitive to asymmetry properties such as spatial inversion symmetry breaking. This sensitivity makes SHG ideal for studying small-scale or delicate materials, including thin films and two-dimensional (2D) systems, positioning it as a key method for investigating antiferromagnetic properties and dynamics. One primary application of SHG is characterizing spatial inversion symmetry breaking induced by antiferromagnetic order. Polarization-dependent SHG signals provide insights into both the material symmetry and the spin configurations. This is particularly useful for materials like chromium oxide and bismuth ferrite, which exhibit intricate antiferromagnetic structures. SHG also excels in probing spin dynamics and phase transitions. By tracking the variation of symmetry and spin structures during phase transitions, such as from paramagnetic to antiferromagnetic, SHG can reveal the phase transition temperatures and mechanisms. Time-resolved SHG experiments can monitor ultrafast spin dynamics with femtosecond resolution, capturing real-time evolution under external perturbations. Another significant application is visualizing magnetic domain structures and magnetoelectric coupling effects. Conventional methods struggle to detect antiferromagnetic domains due to their zero net magnetic moment, but the sensitivity of SHG to local symmetry allows detailed antiferromagnetic domain imaging. For instance, SHG microscopy has mapped magnetic domains in bismuth ferrite thin films, revealing domain configurations and their responses to electric or magnetic fields—Insights crucial for optimizing multiferroic materials. The exploration of 2D antiferromagnetic materials, such as CrI3 and MnPS3, further underscores the versatility of SHG technology. These materials exhibit unique magnetic behaviors and strong spin-lattice coupling due to reduced dimensionality. SHG has identified their distinctive properties, including phase transitions and responses to external fields like magnetic and optical excitation. In summary, SHG technology offers a versatile and sensitive approach for studying antiferromagnetic materials. Due to its ability to probe spatial inversion symmetry breaking, spin dynamics, phase transitions, and magnetic domain structures, SHG has become an indispensable tool for unraveling the complexity of antiferromagnetic order. Future advancements in SHG experimental techniques, such as higher spatial and temporal resolution and the integration with complementary methods, are expected to further enrich its applications. As researchers continue uncovering the micro-mechanisms of antiferromagnetism, SHG will play a pivotal role in advancing both fundamental understanding and technological applications in this exciting field.
DOI: 10.1360/tb-2024-1222
Authors: Shuai Xu, Kui-Juan Jin
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4407206070