The initial magnetic susceptibility of high-concentrated, polydisperse ferrofluids: Universal theoretical expression

In this article, we propose the universal theoretical expression of the ferrofluid initial magnetic susceptibility, which is valid in a wide range of concentrations. The new formula is tested against experimental susceptibility measurements and compared with the well-known second-order modified mean-field theory (MMF2) [Phys. Rev. E 64, 041405 (2001)] and the extended version of MMF2 theory (MMF2 + ) [Phys. Rev. E 96, 052609 (2017)]. It is shown that the new formula is more reliable than MMF2 and MMF2 + theories and predicts initial magnetic susceptibility correctly for the polydisperse ferrofluids within a wide range of both temperature and concentration.