Please forgive me for I have screwed up!

I was in the process of attempting to remove my front brakes so I can put new u-joints in my axle and I broke this piece...

as you can see it is still in one piece but it is cracked on one side of it. I made that tool you see "thinking" to turn that I would be able to loose it and remove my rotor. For what ever reason, the rotor is loose now but I still need to get the other "Nut" or whatever you call it out.
Now my question is, there has got to be an easier way to get these rotor's off. Forgive me because this is my first 4x4 but i need to learn. what tools do I need and where can i get them? Also, what is the name of the piece that I broke and where can I get a new one?
Thanks for your patience.
Andy