Assuming your article isn't open access, then the answer is probably not.
See Springer sharing policies. You can share an accepted manuscript via non-commercial hosting platforms after 12 months. You can't share a published manuscript (note there is a difference between a published manuscript and an accepted one).
Note that just because the article is free right now does not mean it will be free forever. This changes if your article is open access, in which case it will be free forever, and you are free to share it wherever you want (there can be open access articles in subscription journals).
You are free to share the preprint on Researchgate, though, if you still have it.