An internet search reveals quite a few articles written by those who've done deeper studies on this subject. Here are a couple:

http://www.bereanpublishers.com/trouble-in-narnia-the-occult-side-of-c-s-lewis/

http://spaceforswashbuckling.blogspot.com/search/label/Narnia

https://bibleresources.org/witchcraft/