Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)

MA 15.86: Poster

Tuesday, March 27, 2007, 15:00–19:00, Poster A

Magnetzation of Ni_xPt_1−x-Nanoparticles — •Ole Albrecht¹, Detlef Görlitz¹, Kirsten Ahrenstorf², and Horst Weller² — ¹Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg — ²Institut für Physikalische Chemie, Universität Hamburg

We present SQUID-measurements of chemically disordered Ni_xPt_1−x-nanoparticles having a spherical shape (d_mean=4.7 nm), embedded in an organic matrix[1]. These particles are the missing link in the series of 3d-transition-metal/platinum alloys. Zero-field-cooled magnetization reveals superparamagnetic behavior with a characteristic blocking-temperature T_b=7.9 K. Below this temperature the particles show hysteretic behavior with coercive field of H_C(T=5 K)=320 Oe and remanent magnetization of M_rem(T=5 K)=0.293 emu/g. Above T_b the magnetization can be described by the isotropic Langevin superparamagnetic model (ISPM) with a Curie-temperature of T_C=108 K and particle moment of µ_p(T=0)=104 µ_B. The ISPM-behavior contrasts to the anisotropic superparamagnetism (ASPM) previously found in FePt- and CoPt-nanoparticles[2].

[1] K. Ahrenstorf et al., small-journal, DOI:10.1002/smll.200600486

[2] F. Wiekhorst et al., Phys. Rev. B 67, 224416(2003)