Non-dipolar magnetic coupling in a strongly interacting superparamagnet: nanogranular Fe26Cu8Ag66

• Published in: Journal of magnetism and magnetic materials Vol. 266; no. 1-2; pp. 131 - 141
• Main Authors: PANKHURST, Q. A, UCKO, D. H, FERNANDEZ BARQUIN, L, GARCIA CALDERON, R
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Amsterdam Elsevier Science 01.10.2003
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Diamagnetism, paramagnetism and superparamagnetism; Exact sciences and technology; Fine-particle systems; Magnetic properties and materials; Metals and alloys; Physics; Small particles and nanoscale materials; Studies of specific magnetic materials; Muon spin relaxation; Moessbauer effect; FCC lattices; Inorganic compounds; Magnetic relaxation; Ternary alloys; 75.50.Bb; 75.50.Tt; Iron alloys; Superparamagnetism; Dipole interactions; Magnetic susceptibility; Nanoparticles; BCC lattices; 75.75. + a Nanomagnetism; 73.61.Tm; 75.20.-g; Grain size; 75.40.Gb; Magnetization; Magnetic model; Experimental study; Inter-particle interactions; Phenomenological model; Superparmiiagnetismi Nanoparticles; Copper alloys; Silver alloys; Exchange interactions; Transition element alloys
• ISSN: 0304-8853
• DOI: 10.1016/s0304-8853(03)00464-5

Unambiguous evidence for non-dipolar, as well as dipolar, inter-granular interactions has been found in the strongly interacting superparamagnetic mechanical alloy Fe26&MCu8Ag66,. This alloy comprised 5-6 nm BCC Fe-Cu grains in a matrix of similarly sized FCC Ag grains, and was of excellent purity and homogeneity. Magnetic relaxation was measured via DC magnetometry, AC susceptibility, muon spin relaxation and Mossbauer effect experiments. A phenomenological model in which magnetic interactions increased the apparent size of the grains, while retaining the Arrhenius law behaviour of non-interacting grains, predicted the observed variation in blocking temperature as a function of measurement time, with an apparent grain size d* approximately three times larger than the actual size. Significant differences were found in comparisons of temperature-dependent hysteresis data and the predictions of a dipolar interactions model, indicating the additional presence of non-dipolar interactions, most likely RKKY, in the alloy. Corroborating evidence was found in a low-temperature spin-glass-like peak in AC susceptibility data, indicating the possible influence of isolated Fe atoms or clusters within the Ag matrix in mediating inter-granular RKKY interactions.