j is often used instead of i in engineering and physics.

When you start talking about charge density, current, phase and frequency, you almost always start reverting back to engineering notation (i == j). In QM we used i. In Complex Analysis, we used i. In CM, with regards to oscillators/harmonic motion, we used i.

The wikipedia article on imaginary units talks about interchanging i and -j denoting the reversal of plane waves, but we never did that in advanced electrodynamics. However, I wouldn't be surprised if some people do, but as far as I know it's not that common. It's probably find for determining the EM field at some point for some time, but for the problems where you have to find the charge density on a surface of conductor induced by a EM wave, this notation would start to get confusing.