The role of Co2+ cation addition in enhancing the AC heat induction power of (CoxMn1–x)Fe2O4 superparamagnetic nanoparticles

Abstract

The physical role of magnetically semi-hard Co2+ cation addition in enhancing the AC heat induction temperature (T AC) or specific loss power (SLP) of solid (Co x Mn1−x )Fe2O4 superparamagnetic iron oxide nanoparticles (SPIONPs) was systematically investigated at the biologically safe and physiologically tolerable range of H AC (H AC,safe = 1.12 × 109 A m−1 s−1, f appl = 100 kHz, H appl = 140 Oe (11.2 A m−1)) to demonstrate which physical parameter would be the most critical and dominant in enhancing the T AC (SLP) of SPIONPs. According to the experimentally and theoretically analyzed results, it was clearly demonstrated that the enhancement of magnetic anisotropy (K u )-dependent AC magnetic softness including the Néel relaxation time constant τ N (≈τ eff , effective relaxation time constant), and its dependent out-of-phase magnetic susceptibility primarily caused by the Co2+ cation addition is the most dominant parameter to enhance the T AC (SLP). This clarified result strongly suggests that the development of new design and synthesis methods enabling to significantly enhance the K u by improving the crystalline anisotropy, shape anisotropy, stress (magnetoelastic) anisotropy, thermally-induced anisotropy, and exchange anisotropy is the most critical to enhance the T AC (SLP) of SPIONPs at the H AC,safe (particularly at the lower f appl < 120 kHz) for clinically safe magnetic nanoparticle hyperthermia.