Spintronic devices use spin instead of charge to process information and are widely considered as promising candidates for next-generation electronic devices. In past decades, the main motivation in spintronics has been to discover new mechanisms and novel material systems to improve both device performance and the application prospects of spintronics. Recently, researchers have found that ferrimagnetic materials—in which sublattices are coupled antiferromagnetically—offer an emerging platform for realizing high-density, high-speed, and low-power-consumption memory and logic functions. Within such a ferrimagnetic class, vanishing magnetization and ultrafast magnetic dynamics can be achieved by adjusting chemical composition and temperature, among other parameters. Meanwhile, unlike for antiferromagnets, conventional electrical read–write methods remain suitable for ferrimagnets, which is beneficial for applications. In this review, an abundant class of ferrimagnets including oxides and alloys is surveyed, and unique magnetic dynamics and effective methods for manipulating the magnetic states of ferrimagnets are discussed. Finally, novel storage and computing devices based on ferrimagnets are considered, as there are some challenges to be addressed in future applications of ferrimagnets.

Spintronic thin films were shown to be promising high-performance broadband terahertz (THz) emitters. For spintronic ferromagnet/heavy metal heterostructures, THz emission arises from three mechanisms: the magnetic dipolar radiation due to the ultrafast demagnetization, the transient current radiation due to spin-charge conversion, and anomalous Hall effect. Here, we demonstrate that the three mechanisms show distinct dependences on the thickness of the ferromagnetic layer. With the insertion of an ultrathin ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer between the ferromagnetic and heavy metal layer, the spin-charge conversion is suppressed when the ${\mathrm{Al}}_2{\mathrm{O}}_3$ thickness exceeds 1 nm. Our results agree with the theoretical predictions based on a simple spin-diffusion model.

All optical switching (AOS) of magnetization exhibits a high potential for ultrafast and energy-efficient memory applications. Many works have been carried out in the area of AOS, including its observation in a wide variety of ferromagnetic or ferrimagnetic materials, and the exploration of the parameters for the achievements of AOS such as the laser fluence and helicity, and duration of laser pulses. A large majority of all optical helicity-independent single-shot switching (AO-HIS) has been observed in Gd-based rare-earth transition-metal ferrimagnets. It is then necessary to explore the unique role of Gd in AO-HIS mechanism, compared with other rare-earth elements. Here, we engineered ${\mathrm{Gd}}_{1-x-y}{\mathrm{Tb}}_y{\mathrm{Co}}_x$ alloys and investigated the influence of the Tb concentration on the magnetization dynamics via static Kerr microscope and time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. The ultrafast demagnetization time at low fluence is found to be independent of Tb concentration, while both the range of laser fluence and pulse duration allowing for AO-HIS becomes narrower with increasing the Tb concentration. The TR-MOKE signal $\mathrm{\Delta }{\mathrm{\Theta }}_K/{\mathrm{\Theta }}_{K\_\mathrm{sat}}\sim 10\mathrm{ps}$ after the laser pulse excitation decreases with increasing either the Tb concentration or the pulse duration. The fact that AO-HIS is prohibited by increasing the Tb content is explained by considering a larger damping for Tb than Gd in atomistic simulations. Our results are well explained by the fact that angular momentum can be transferred from Gd to Co resulting in the magnetization switching, whereas for Tb it is dissipated through the lattice due to the large spin-orbit coupling, instead of being transferred between Tb and Co.

Single-pulse magnetization switching by femtosecond laser pulses is the fastest way to manipulate magnetization. To date, among rare-earth transition metal alloys, single-pulse switching is limited to Gd-based structures. Here, we demonstrate ultrafast single-pulse switching of Tb-dominant CoTb alloys within several tens of picoseconds. Our further analysis shows that the ultrafast magnetization reversal is linked to ultrafast heating of laser pulses and an external field.

Spintronic thin films are considered as one of the promising terahertz (THz) source candidates, owing to their high performance and low cost. Much effort has been made to achieve spintronic THz sources with broadband and high conversion efficiency. However, the development of spintronic THz emitters with good compatibility, low cost, and miniaturized technology still faces many challenges. Therefore, it is urgent to extend commercial and portable spintronic THz emitters to satisfy many practical applications. Herein, we design a new generation of spintronic THz emitters composed of an alternating electromagnet and a miniaturized electronic controller. Not only can this new type of spintronic THz emitter largely simplify the ancillary equipment for spintronic sources, it also has a twice larger THz signal compared to the traditional THz time-domain spectroscopy systems with a mechanical chopper. Experimental results and theoretical calculations for electromagnetic coils show that our design can stably generate THz signals that are independent of the frequency and magnetic field of alternating signals. As the spin thin film is optimized, a magnetic field as low as 75 G satisfies the requirement for high performance THz emission. Hence, not only is the efficiency of the pump power enhanced, but also the driving current in the electromagnet is decreased. We believe that it has a wide range of applications and profound implications in THz technology based on spintronic emitters in the future.