An atomic clock may include substantially isolated particles that are capable of exhibiting hyperfine transitions. An alignment device of the clocks may establish a predominant direction of spin of the particles. The clocks may include an excitation device to, at regular intervals of time, cause the particles to undergo the hyperfine transitions by exciting the particles. A detection device of the clocks may detect the hyperfine transitions of the particles. In an aspect, the particles may be included in a layer over a substrate. In an aspect, the detection device may include a magnetoresistive sensor. In an aspect, the atomic clock may fit within one cubic millimeter. Methods of making the atomic clocks and systems in which the atomic clocks may be employed are also disclosed.