  Significant progress has been made in answering fundamental questions about
how and, more importantly, on what time scales interactions between electrons,
spins, and phonons occur in solid state materials. These complex interactions
are leading to the first real applications of terahertz (THz) spintronics: THz
emitters that can compete with traditional THz sources and provide additional
functionalities enabled by the spin degree of freedom. This tutorial article is
intended to provide the background necessary to understand, use, and improve
THz spintronic emitters. A particular focus is the introduction of the physical
effects that underlie the operation of spintronic THz emitters. These effects
were, for the most part, first discovered through traditional spin-transport
and spintronic studies. We therefore begin with a review of the historical
background and current theoretical understanding of ultrafast spin physics that
has been developed over the past twenty-five years. We then discuss standard
experimental techniques for the characterization of spintronic THz emitters and
- more broadly - ultrafast magnetic phenomena. We next present the principles
and methods of the synthesis and fabrication of various types of spintronic THz
emitters. Finally, we review recent developments in this exciting field
including the integration of novel material platforms such as topological
insulators as well as antiferromagnets and materials with unconventional spin
textures.
