Any really good R&B singers that you would like to recommend? Not too fast R&B.?

I mean singers that sing like Rihanna. I perfer kinda slow type of R&B, not fast ones.
I already know Mariah Carey...I don't really like her don't mention her. Of course I already heard of Rihanna too.
Update: oh yeah..forgot to add:
I only want female r&b singers
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