E!ect of interparticle interactions in (Fe0.26Ni0.74)50B50 magnetic nanoparticles

ZYSLER ROBERTO; RAMOS CARLOS; DE BIASI EMILIO; ROMERO HÉCTOR; ORTEGA A.; FIORANI DINO

Barcelona, España

Congreso; III International Workshop on Magnetic Fine Particle and Their Relevance to Materials Science.; 1999

The magnetic properties of amorphous (Fe 0.26 Ni 0.74 ) 50 B 50 nanoparticles (mean diameter: 2 nm), synthesized by chemical route, have been investigated by magnetization measurements. The results obtained on a powder sample and on homogeneous diluted dispersion of particles in a polymer matrix, prepared from the same batch, are compared. The dispersed sample shows the characteristic behaviour of an assembly of independent magnetic nanoparticles, with narrow size distribution, whose moments block progressively with decreasing temperature: the zero "eld cooled magnetization,"eld cooled magnetization, M ZFC , shows a narrow maximum (¹.!9"55 K), whereas the "eld cooled one (M¹.!9"55 K), whereas the "eld cooled one (M FC ) increases continuously with decreasing temperature; in the high-temperature superparamagnetic regime, the magnetization curves are satisfactorily "tted to a superposition of Langevin functions, due to the volume distribution. In the powder sample, because of interparticle interactions, ¹.!9 increases (¹.!9+100 K) and Mtted to a superposition of Langevin functions, due to the volume distribution. In the powder sample, because of interparticle interactions, ¹.!9 increases (¹.!9+100 K) and M¹.!9 increases (¹.!9+100 K) and M FC shows a plateau below+30 K. Moreover, signi"cant changes are observed at low temperature in the shape of the hysteresis cycles and in the temperature dependence of the remanent magnetization and coercive "eld, both showing a maximum at+15 K. The observed features suggest a change of regime at low temperature to a disordered collective magnetic state of particle moments.+30 K. Moreover, signi"cant changes are observed at low temperature in the shape of the hysteresis cycles and in the temperature dependence of the remanent magnetization and coercive "eld, both showing a maximum at+15 K. The observed features suggest a change of regime at low temperature to a disordered collective magnetic state of particle moments."eld, both showing a maximum at+15 K. The observed features suggest a change of regime at low temperature to a disordered collective magnetic state of particle moments.