Ferromagnetic Properties of Single-Crystal Nickel Platelets and Submicron Whiskers

Abstract

Nearly perfect nickel, nickel alloy, and iron single-crystal platelets of thin-film thickness are excellent specimens for basic ferromagnetic domain, domain-wall,1,2 and resonance3 studies. Submicron nickel whiskers that grow with the platelets are also ideal for nucleation studies.4 Individual whiskers as thin as 600 Å (2 pg) are readily observed (by Rayleigh scattering), tested, and handled. Physical buckling of the whiskers into forms of the elastica5 allows measurements of both end and infinite-rod nucleation fields. Observed fields versus whisker diameter and versus field angle follow curling theory.6 Thickness comparisons by electron microscopy and by bending yield an effective Young's modulus near 10×1111 dyn/cm2, about half the handbook value. A motion-picture film showing the physical bending and the magnetic nucleation of whiskers suspended in a thin layer of oil and viewed through a microscope by dark-field illumination was presented at the conference. The platelets show with classic simplicity many details of domain and domain-wall structure and behavior, making them especially suitable for educational purposes, for testing theories, and for supplementing thin-film studies. Recent platelet observations include double 90° and 180° Bloch walls; a double wall apparently composed of 180° walls of mixed Néel-Bloch character; 180° Bloch walls that may press against a platelet edge without parting; 45° walls formed by magnetostrictive anisotropy; a field-induced stripe pattern in [100] Ni-Co platelets with +K1; and the transitional domain structure in a Ni-Co platelet with a linear variation in composition from +K1 to −K1.