No abstract

Single-phase α''-Fe16N2 nanoparticles have been synthesized with high reproducibility in gram amounts for the first time. The nanoparticles were obtained through the various kinds of successive procedure starting from the reduction of Fe-oxides, followed by nitriding in an atmosphere with very low moisture and oxygen contents of less than 1 ppm through the entire process. The single-phase α''-Fe16N2 nanoparticles exhibited saturation magnetization (Ms) of 234 emu/g at 5 K and a magnetocrystalline anisotropy constant (Ku) of 9.6×106 erg/cm3. These magnetic properties of this α''-Fe16N2 nanoparticles suggest that a new path for a possible candidate of the rare-earth-free permanent magnet material with a high Ms.

In order to determine the value of the intrinsic magnetic moment of the α ″ phase, the films of nitrogen-martensite with various N content were fabricated under various reactive sputtering conditions. The magnetic moment of (α ″+α′)-Fe16N2 films is discussed in connection with the change of the unit-cell volume of the bct structure and the degree of N site ordering in nitrogen-martensite. As a result, it is found that (1) the same structure as bulk α ″-Fe16N2 is realized in the present films, (2) the saturation magnetization σs of the α′ phase increases about 4% with increasing unit-cell volume of the α′ phase, (3) the degree of N site ordering from α′ to α ″-Fe16N2 does not much affect σs, and (4) the experimentally obtained maximum value of σs for the (α ″+α′)-Fe16N2 film was 232 emu/g. The intrinsic value of σs in the α ″ phase (in the perfectly ordered state) is proposed to be no more than 240 emu/g at 300 K.

Magnetic iron oxide nanoparticles (MIONPs) were synthesized in a FeCl₂-NaNO₃-NaOH aqueous system under various initial Fe(2+)/NO⁻₃ molar ratios (α) and Fe(2+)/OH- molar ratios (β) in order to clarify the effects of the initial molar ratio of reactants on the reaction mechanism. The Fe(2+)/NO⁻₃ /OH(-) molar ratio of 3 : 1 : 5 led to the formation of magnetic nanoparticles mainly composed of magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃). The 36 nm sized γ-Fe₂O₃ and 413 nm sized Fe₃O₄ were obtained by changing the order in which NaNO₃ was added to a NaOH solution. The in vitro heat generations of the resulting MIONPs in an agar phantom were measured under an alternating magnetic field (100 kHz, 23.9 kA/m). The temperature rise (ΔT) of the agar phantom for the 36 nm sized γ-Fe₂O₃ was 55°C in the first 140 s, with a concentration of 58 mg Fe/mL. Our results showed that it is possible to prepare MIONPs with high heating efficiencies under optimal conditions using the present method.

The in-plane Fe spin spiral structure for Fe/Sm-Co(1100) exchange-spring magnetic bilayers was investigated by 57 Fe conversion electron Mössbauer spectroscopy during the magnetization reversal process, and correlated with hysteresis loops measured via the longitudinal magneto-optic Kerr effect. A direct experimental proof for a relaxed spiral angular spin distribution in the Fe layer is presented. Under negative applied fields the interfacial Fe spins rotate by up to 40°with respect to the easy axis of the Sm-Co hard-magnet layer.