Electrical engineers use j for the square root of -1 while nearly everyone else uses i. The usual explanation is that EE’s do this because they use i for current. But here’s one advantage to using j that has nothing to do with electrical engineering.
The symbols i, j, and k are used for unit vectors in the directions of the x, y, and z axes respectively. That means that “i” has two different meanings in the real plane, depending on whether you think of it as the vector space spanned by i and j or as complex numbers. But if you use j to represent the imaginary unit, its meaning does not change. Either way it points along the y axis.
Said another way, bold face i and italic i point in different directions But bold face j and italic j both point in the same direction.
Here’s what moving from vectors to complex numbers looks like in math notation:
And here’s what it looks like in electrical engineering notation:
I don’t expect math notation to change, nor would I want it to. I’m happy with i. But using j might make moving between vectors and complex numbers a little easier.
Related: Applied complex analysis