Defamation? Retaliation?

A co-worker made a false report to HR, that I am a racist and a bully. This coworker and I have history. I reported her for violating the HIPPA law. She was suspend for two weeks. Since then, I've been cussed out twice and falsely reported several times. Management has ran with this false info, told this info to different mangers and other coworkers. The last incident, of her yelling at the top of her lungs cussing me out, their were three witness. I report this to HR and they conduct an investigation but, ask MY witness was I bullying her. Although, all three witness state I said nothing to her. HR is also, trying to get people to say they were in that area and make a false statement against me. Can I sue for defamation of character?? Would this be consider retaliation??