I'm not sure if angels are material or spirit. I've not studied that at all.
Then why do you believe in them?
And what exactly would you "study" to find out if angels were material or spirit. Since there is no evidence that any angels exist to "study". By "study" do you mean pointless guessing and speculation?
I suggest that we also "study" whether unicorns are invisible or not. How about "studying" whether or not Vulcans actually have copper-based green blood? Or "studying" which brand of deodorant Bigfoot prefers to use? (I would say Axe.)