Can I create another Model beside MY_Model.php?

I now have application/core/MY_Model.php that extend CI_Model. I'd need to create another MY_Article_Model.php in the same path (I'm not sure it's a good idea to create MY_Article_Model.php), but an error appeared(see my image). Can I create another model or not? If not, what Should I do?
My Folders:
- application/controllers/admin/Article.php
- application/core/MY_Model.php
- application/core/MY_Article_Model.php
- application/models/article_m.php (class Article_m extends MY_Article_Model.php) Fatal Error!