From a quick skim of Wikipedia articles for each of them, they seem largely unrelated. Thermal hysteresis seems to be the range of temperatures at which a solution will undergo a given state change. Hysteresis in general seems to be the phenomenon of systems which undergo a lagged reaction to the addition and then removal of a force and it's effect. Electromigration seems to be the process of actual material moving around during the operating life of a circuit.
Other than that, I'd never heard of the two before :icon_wink:
In fact, what you just said makes them seem pretty related. State changes in materials usually do occur as a result in temperature change and it is usually a progressive transition that can occur over a range of temperatures.
I had meant to add the following but multitasking took me over the thirty minute limit for editing, so here's the rest of the information.
Electromigration has been around for about a hundred years but didn't have real relevance until the about 1966 with the advent of the IC. One of the considerations in designing ICs is the high temperatures which break down the copper traces, so much so that there is a test called the high temperature over life which can determine the life expectancy of an IC in a given situation. Through combining different alloys and annealing they have made significant improvements, but the heat issue still exists. I will be interested to see what will happen in the near future, there are companies experimenting with the use of fiber optics for connections which will not only eliminate the electromigration problem but should also be appreciably faster.