Superparamagnetic particles, process for producing the same and their use

Process for producing superparamagnetic particles of uncoated single-domain particles and stabilizer substances comprising

• producing superparamagnetic uncoated single-domain particles from iron oxide, iron mixed oxide or iron with a particle size in the range between 3 and 20 nanometers by precipitation from aqueous iron salt solutions with lye or ammoniacal liquor in the pH range of 8.0 to 10.0,
• adjusting to a pH of between 3 and 6 with an acid and aggregating at a temperature in the range of 50 to 120.degree. C. and optionally elevated pressure in this pH and temperature range, to form aggregates having a particle size in the range between 10 and 1000 nanometers;
• purifying the aggregates and reacting with 20 to 50% by weight of stabilizer substances to form coated aggregates,
• the stabilizer substance being selected from the group comprising phosphate, diphosphate, carboxylate, polyphosphate, thiophosphate, phosphonate, thiophosphonate, sulphate, sulphonate, mercapto, silanetriol, trialkoxysilane group-containing polyalkylene glycols, the carbohydrates or the phosphate group-containing nucleotides, the oligomers thereof or the polymers thereof;
• and
• purifying the stable, decomposable coated aggregates obtained in the magnetic field and are optionally further coupled to pharmacologically or diagnostically active substances.