* Astronomy

Title: Heavy Fermion-like metal alpha double prime-Fe16N2 with giant saturation magnetisation
Authors: Nian Ji, Xiaoqi Liu, Jian-Ping Wang

A new model is proposed for the strong ferromagnetism associated with partially localised orbitals in the Fe16N2 metallic system which draws substantially from models of heavy fermion metals. We demonstrated that an unusual correlation effect is brought up within the Fe-N octahedral cluster region and the effective on-site 3d-3d Coulomb interaction increases due to a substantial 3d electrons charge density difference between the clusters and its surroundings, which leads to a partially localised high spin electron configuration with a long range ferromagnetic order. First principle calculation based on LDA+U method shows that giant magnetic moment can be achieved at sufficiently large Hubbard U value. The feature of the coexistence of the localised and itinerant electron states plays a key role on the formation of the giant saturation magnetisation.

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Title: Magnetism of alpha(double prime)-Fe16N2
Authors: Metzger, Robert M.; Bao, Xiaohua; Carbucicchio, Massimo

The metastable alpha(double prime)-Fe16N2 phase may have a magnetic moment up to 50% higher than that of pure bulk alpha-Fe. This article addresses the following issues. (1) Can epitaxial films of alpha(double prime)-Fe16N2 be prepared phase pure? Yes, but there are some doubts.
(2) Can powders of alpha(double prime)-Fe16N2 be prepared phase pure? Not yet.
(3) Is the Mossbauer spectrum due to alpha(double prime)-Fe16N2, to martensite, or to something else? Most assign it to alpha(double prime)-Fe16N2.
(4) What is the specific saturation magnetic moment of alpha(double prime)-Fe16N2? Some claim it is close to that of alpha-Fe, most claim that it is much larger.
(5) Is the high moment due to alpha(double prime)-Fe16N2, or to some other phase?

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