Magnetic transducers

A method for the production of nanoparticles comprising the following steps:

• A1) providing a composition of at least one iron-containing compound A in at least one organic solvent LM1, wherein the at least one iron-containing compound A is selected from the group consisting of iron complex compounds, iron carbonyl compounds, iron salts, organic iron compounds, and iron-sandwich-complexes, and wherein the at least one organic solvent LM1 is a high boiling solvent;
• B1) heating of the composition to a temperature in the range of 50° C. to a temperature of 50° C. below the actual reaction temperature of the iron-containing compound A according to step C1 for a minimum period of 10 minutes;
• C1) heating of the composition to an actual reaction temperature between 200° C. and 400° C. to obtain particles, wherein the heating step is carried out for at least 30 minutes;
• D1) purifying the obtained particles, wherein the purification is performed by Soxhlet extraction;
• E1) suspending the particles in water or an aqueous solution of an acid;
• F1) adding a surface-active compound;
• I1) producing a dispersion of the particles in a solvent mixture of (i) water and (ii) a solvent miscible with water;
• and
• J1) adding an alkoxysilane to the dispersion of the particles in the solvent mixture according to step I1);
• wherein the method further comprising step X2) following steps C1 or E1 or F1 or I1 or J1:
• X2) oxidizing the formed particles by suspending the particles in 0.5 to 2M HNO3, adding an Fe(III) salt and boiling the particles under reflux;
• and
• wherein the nanoparticles have a specific absorption rate (SAR) of 10-40 W per g Fe at a field strength of 4 kA/m and at frequency of an alternating magnetic field of 100 kHz.