Studies of two- and three-dimensional ZnO:Co structures through different synthetic routes

Abstract

Multilayers of Co and ZnO, with nominal layer thicknesses on the atomic scale with up to 25 bilayers, were deposited by ion beam sputtering on silicon and glass substrates at ambient temperature. Thick epitaxial Co x Zn 1Ϫx O films on Al 2 O 3 (012) substrates were grown by metalorganic chemical vapor deposition using a liquid precursor delivery system. All were co-doped with Al. Comparative analysis of magnetization, resistivity, and magnetoresistance measurements, performed in the temperature range 2.5-300 K, is presented. At small thickness of Co layers in the multilayer samples, these structures are diluted magnetic semiconductor ͑DMS͒ superlattices, with properties close to the epitaxial films. A crossover from DMS to discontinuous magnetic metal/ semiconductor multilayers is observed with increasing metal content in the multilayers. This leads to changes in conduction mechanisms, with increasing contribution of quasithree-dimensional or quasitwo-dimensional intergranular hopping, and superparamagnetism.

Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films

“…[265][266][267][268][269][270][271][272][273][274][275][276][277] As an example of the interesting and potentially useful physics that has been gleaned from studies of oxides grown by sputtering, we consider the observation of a giant planar Hall effect in epitaxial doped manganites. The planar Hall effect occurs in magnetic materials when the resistivity depends on the angle between the direction of current flow and the magnetization, the effect being otherwise known as anisotropic magnetoresistance.…”

Nanoparticles of ZnO Doped With Mn: Structural and Morphological Characteristics

“…It has been extensively investigated for various applications such as varistors 1 , transparent transistors 2,3 , sensors 4 , and UV light emitting devices 5,6 . The prediction 7 that p-type ZnO and GaN may exhibit ferromagnetism characteristic above room temperature in response to doping with Mn has initiated intensive experimental work on a variety of doped diluted magnetic semiconductors (DMS) [8][9][10][11][12][13][14] . Diluted magnetic semiconductors (DMSs), and particularly ferromagnetic oxides, are potential candidates for technological applications such as spin-transistors or the ultra-dense nonvolatile semiconductor memories 15 .…”

The magnetic properties of Co-doped ZnO diluted magnetic insulator films prepared by direct current reactive magnetron co-sputtering

“…Since then, there has been much attention on the doping ZnO system as a potential DMS to provide efficient injection of spinpolarized carriers for spintronic devices. Room temperature ferromagnetism has been obtained in this system, such as Co : ZnO [4][5][6][7][8][9][10][11][12], Mn : ZnO [13,14], Ni : ZnO [15], V : ZnO [16]. All these doping ZnO films prepared by pulsed-laser deposition [4][5][6][7]13,14], ion beam sputtering [8], metalorganic chemical vapor deposition [8,9], combinatorial laser molecular-beam epitaxy [11], solution synthesis [10,15] and reactive magnetron co-sputtering [12] are either conducting or semiconducting, which are characterized by localized d electrons of the transition-metal ions strongly couple with the extended sp carriers of ZnO.…”

“…Thus, the carriers are spin-polarized and able to mediate ferromagnetic ordering of the magnetic moments of transition-metal ions doped into the oxide lattice. Also, this sp-d exchange interaction induces interesting magneto-optical and magneto-electrical properties [7][8][9][10].…”