A Compton scattering study of the magnetic structure of NbFe$_2$

NbFe$_2$ displays a diverse phase diagram over a narrow compositional range, possibly due to close proximity to a Quantum Critical Point. The ground state of NbFe$_2$ has been the subject of a number of recent theoretical investigations [1,2], but for near-stoichiometric compositions its exact nature remains ambiguous. We have probed the low temperature magnetic structure by performing Magnetic Compton Scattering (MCS) measurements on polycrystalline Nb$_{1+y}$Fe$_{2-y}$ samples with $y=-0.02,0.00$ and $0.03$. MCS is able to measure how the magnetic electrons within a sample are distributed in momentum space, and can be a useful tool for resolving site-specific contributions to the spin moment. The interpretation of these measurements was aided by electronic structure calculations, which favour a ferrimagnetic ground state. The results are presented with reference to the possible presence of spin fluctuations. \\[4pt] [1] Subedi and Singh, PRB {\bf 81}, 024422 (2010) \\[0pt] [2] Tompsett et al, PRB {\bf 82}, 155137 (2010)