Origin of ferromagnetism in ZnO∕CoFe multilayers: Diluted magnetic semiconductor or clustering effect?

• Published in: Applied physics letters 2004-10, Vol.85 (17), p.3815-3817
• Main Authors: Huang, J. C. A., Hsu, H. S., Hu, Y. M., Lee, C. H., Huang, Y. H., Lin, M. Z.
• Format: Article
• Language: English
• Subjects: ABSORPTION SPECTROSCOPY; ALUMINIUM OXIDES; BINARY ALLOY SYSTEMS; COBALT ALLOYS; DEPOSITION; FERROMAGNETISM; FOURIER TRANSFORMATION; ION BEAMS; IRON ALLOYS; MAGNETIC PROPERTIES; MAGNETIC SEMICONDUCTORS; MAGNETIZATION; MATERIALS SCIENCE; SPIN WAVES; SPUTTERING; SUPERPARAMAGNETISM; TEMPERATURE RANGE 0273-0400 K; THREE-DIMENSIONAL CALCULATIONS; X-RAY SPECTRA; X-RAY SPECTROSCOPY; ZINC OXIDES
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.1812844

Epitaxial growth of (0001) oriented [ZnO(20Å)∕Co0.7Fe0.3(xÅ)]25 multilayers (MLs) with nominal thickness x=1, 2 and 5 has been prepared on α-Al2O3 (0001) substrate by ion-beam sputtering. The magnetic properties over a temperature range of 6–350K and structures probing by x-ray absorption spectroscopy (XAS) are reported. Above room-temperature ferromagnetism has been observed for x=1 and x=2 MLs, while superparamagnetic behavior dominates for x=5 ML. The field-cooled magnetization-temperature M(T) curves of x=1 and x=5 MLs can be fitted by a standard three-dimensional (3D) spin-wave and a Curie–Weiss model, respectively. For x=2 ML, however, neither a 3D spin-wave nor a Curie–Weiss model, but a combination of the two fits the M-T curve. The XAS studies together with the magnetic measurements further reveal that x=1 sample behaves as a diluted magnetic semiconductor (DMS) ML, while x=2 ML shows a mixed structure consisting of a minor component of DMS and a major component of CoFe clusters. A predominant clustering phase appears for x=5 ML.