Is hair used for black magic?

Yes it is considered by those who study types of magic to be used in sympathetic magic, specifically with outcomes of contagious magic where a severed hair is considered to retain a a magical sympathy with the person to whom it had been attached. It is used to perform black magic causing damage to that person to whom it belonged. This outcome falls under shamanism and used to control or conjure spirits to do the practitioner's bidding. See David S. Noss, A History of World's Religions, 11th ed. p. 11.