Dipolar ordering in NPs by holography

Dipolar ferromagnetic phase transition in Fe3O4 nanoparticle arrays observed by Lorentz microscopy and electron holography.
Kazuo Yamamoto, Charles R. Hogg, Saeki Yamamuro, Tsukasa Hirayama, and Sara A. Majetich
Appl. Phys. Lett. 98, 072509 (2011)

Temperature dependence of magnetic induction maps determined from the reconstructed phase images.