Hello there,
i am also a recent joinee in Ph.d, my major is into psychometric; i am sure the scope would be there in future for PH.d s in HR, simultaneously you should also have an experience of min 8 -10 years while completing of your studies. if you strongly have a passion and enthusiastic in HR, please go for it also i can advice you choose the best university or college for this unless your research will not have better scope.
all the best