The role of Co 2+ cation addition in enhancing the AC heat induction power of (Co x Mn 1-x )Fe 2 O 4 superparamagnetic nanoparticles.

The physical role of magnetically semi-hard Co 2+ cation addition in enhancing the AC heat induction temperature ( T AC ) or specific loss power (SLP) of solid (Co x Mn 1- x )Fe 2 O 4 superparamagnetic iron oxide nanoparticles (SPIONPs) was systematically investigated at the biologically safe and physiologically tolerable range of H AC ( H AC,safe = 1.12 × 10 9 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 susceptibilityχ″primarily caused by the Co 2+ 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.