Good question, Polarization was found from junction based measurements. Check this one out. I do not remember any thing more than this. "Negative spin polarization of Fe3O4 in magnetite/manganite-based junctions"Phys Rev Lett. 89 276601, and Schottky barrier and spin polarization at the Fe3O4-Nb:SrTiO3 interface Phys. Rev. B 71, 180406.

if we talk about 100% spin polarization then until now its just a theoretical prediction but 80% spin polarization has been achieved in magnetite epitaxial films like you can find it in "Evidence for the half-metallic ferromagnetic state of Fe3O4 by spin-resolved photoelectron spectroscopy"

Mueller et al (Nat Mater 8, 56-61) used time-resolved MOKE and found indirect evidence due to the absence of ultrafast spin-flip scattering.

Our paper, appearing soon in Phys.Rev.B (proofs sent to the editor), brings some more evidence in favour of half-metallicity; its title:

"Fe t2g band dispersion and spin polarization in thin films of Fe3O4(0 0 1)/MgO(0 0 1):

Half-metallicity of magnetite revisited", by W. Wang et al.

Also check out Pratt et al. PHYSICAL REVIEW B 85, 180409(R) (2012)

Surface spin polarisation on magnetite (111).

Half-metallicity (in the DOS) has proved tricky to demonstrate unequivocally: spin resolved photoemission may pick up near-surface non-stoichiometry, etc.

Nonzero T effects: PRB 85 (2012) 060403 gives an ab initio theory of spin polarisation collapse in half-metals.

@ Karol Hricovini - Looking forward to seeing your paper!

You can also look at an old paper:

Phys. Rev. Lett. 34, 319–322 (1975)

Observation of Spin-Polarized Electron Levels in Ferrites

This is also about spin polarized photoelectron spectroscopy.

Here is the link to our paper:

http://link.aps.org/doi/10.1103/PhysRevB.87.085118

We have study were the ALD iron oxide thin films doped with MgO this work includ Verwey trasition also. http://jss.ecsdl.org/content/2/3/N45.abstract

O.K. my answer in this category will be elucidating by the fact there are two ores,known specifically,Haemetite and magnetite.Both of the ores will be 100% magnetize over a 100% domain alignment,otherwise Half metal for the case of 50% alignment.

Sorry, Sanket, but haematite (= alpha-Fe2O3) has nothing to do with Fe3O4, while magnetite actually IS Fe3O4. And half-metallicity as well as degree of polarization at the Fermi level seem still to be controversial to me (but I may be somewhat outdated on this one).

Thanks for all the answers. Specially to Karol for his new work, and to Hermann for the NatMat reference on ultrafast MOKE (I was aware of the older PES work) . For the time being, I feel like Kai: I am still skeptic. I think PES is too affected by the surface structure (positive surface pol in 111!), and even then, there are a lot of "negative" results. Well, makes life interesting.