JKR's idea of horcruxes

[Auria]

No: HPFGUIDX 140316

Something that I have been wondering (nothing really to do with the HP 
plot but very relevant all the same) is where did JKR get the idea of 
horcruxes?  I mean its a very unusual concept - to split one's soul 
and 'keep' a piece in a separate place to gain immortality - and I 
wonder if JKR had gotten this idea from any other literature somewhere 
or if its entirely unique? Just my curiosity really, but does anyone 
have any thoughts about this?  Afterall, its a very creepy idea isn't 
it!
Auria