Correlation between the structural and transport properties of as-grown epitaxial phase-separated Co-Ag thin films

Abstract

Giant magnetoresistive Co-Ag granular films are prepared by molecular beam epitaxy at three different temperatures with cobalt concentrations ranging from 30 to 80 at. %. The structural properties of these films are studied using a variety of diffraction techniques and real space probes. Magnetization and magnetotransport measurements are carried out at room temperature. Correlating the structural and magnetotransport properties reveals that the spin diffusion length strongly affects the amplitude of the giant magnetoresistance, which is otherwise dominated by the surface-to-volume ratio of the segregated magnetic precipitates.

Structural and magnetic properties of Al doped Co–Ag granular films: temperature dependence of magnetoresistance

“…The post-annealing causes first an increase in MR and then a decrease for both STA (10 min) [1], and LTA (30 min) [11]. A similar behaviour was reported for films deposited at substrate temperatures between 300 and 723 K for CoAg [10], and between 300 and 773 K for FeAg films [8]. These authors reported that Rð0Þ decreases more rapidly than DR with annealing temperature causing a temperature dependence of MR as mentioned.…”

“…In particular, the CoAg granular films, exhibiting the largest GMR value at room temperature, were extensively investigated [1,4,8,[9][10][11][12]. In granular systems, the GMR effect is caused by spindependent scattering at the interfaces between the ferromagnetic grains and the nonmagnetic matrix and spin-dependent scattering within ferromagnetic grains [13,14].…”

Improved giant magnetoresistance in nanogranularCo∕Ag: The role of interparticle RKKY interactions

“…3 In both types of nanoscale systems, the GMR arises from spin-dependent electron scattering, 3,4 yielding a reduced resistivity when the magnetic layers/nanoparticles are aligned. Shortly after its discovery, a similar GMR effect was reported for various granular systems, the most intense one being observed in the Co/ Ag system, [5][6][7][8][9][10][11][12] the subject of this article: Xiao et al achieved a 24% GMR (at room temperature, RT, and 50 kOe applied field) in a 28% at. Co concentrated (20% vol.)…”

“…6,11 Thermal treatments affect the GMR properties of sputtered and melt-spun immiscible alloys, since these nonequilibrium synthesis methods produce supersaturated solid solution matrices that will segregate the magnetic species upon annealing. 13 Such variations have been mostly related to the growing particle size, or to changes in the quality of the particle/matrix interface, 14 whereas little attention has been paid to the role of the matrix microstructure/composition, 10 customarily thought to affect the GMR ratio only through its resistivity. 15 However, in the context of spin-glass phenomenology in granular samples, López et al have proved recently the important role of interparticle RKKY-like interactions enhanced by the presence of Co solute atoms in the matrix.…”

Nanoscale Fe islands on MgO(001) produced by molecular-beam epitaxy

“…However, both measuring and controlling the properties of an inhomogeneous system are difficult, and few studies report the correlation of transport and structural properties. 5 Here we report a method by which a granular system can be formed. When Fe is grown at temperatures above 700 K, a sharp transition occurs, resulting in the formation of discontinuous islands instead of the continuous films previously reported.…”