the
kartika is a
ceremonial weapon used in some rituals to cut the bonds of ignorance, in other rituals to chop up demons. It is used in conjuction with the
kapala (actually made of a person's top half of the skull!

). I will upload pictures of the one I have in a day or so.
Another note: the phurba in some ceremonies is used to pin down the demon or evil spirit so the lama can have more control. Sometimes you will see a horse head on top. It is the form of a deity that frightens demons (the name escapes me at present).