Magnetic Correlations Close to Quantum Critical Point in the Disordered Ferromagnetic Alloys Ni-V Observed with SANS*

We present a small-angle neutron scattering (SANS) analysis of the ferromagnetic (FM) alloys Ni_1-xV_x where the FM order is destroyed towards a paramagnetic phase by sufficient substitution of Ni by V. The critical temperature T_c vanishes at x_c=0.116 indicating a quantum critical point (QCP) with signatures of disorder [1]. We performed polarized SANS experiments on different Ni_1-xV_x polycrystalline samples close to x_c at NG7SANS, NCNR, NIST utilizing a ³He cell within the wave vector regime Q=0.06-1nm^-1. We could resolve magnetic scattering at different length scales within the FM state well below T_c<50K [2]. We find isotropic magnetic short-range correlations as well as anisotropic magnetic contributions that reveal large scale magnetic domains and an indication of local magnetic defects that relates to the V concentration. We show how these different contributions respond to high magnetic fields and evolve with V concentration x, characterizing a disordered FM alloy, close to the QCP.
[1] R. Wang et al, Phys. Rev. Lett. 18, 267202 (2017)
[2] A. Schroeder et al, AIP Adv.10,015036 (2020)