The headpiece of spermatozoa is protected by a type of tough membrane to which the acrosome is attached underneath.  You must first find a way to crack open this protective layer of membrane and acrosome before you can fractionate the sperm head.  HTH.

Actually I was sonicated (Probe) the mouse sperm for 5Sec and it was separated both Head and Tail. Since, I used different types of density gradient (Sucrose) as mentioned in the reference articles but it was not successed to separate both and the head was not soliblized in solublizing buffer (5m Guanidine, 0.5M Tris-HCl, 2M Urea, Protease inhibitor).