Ferromagnetic nanocomposites as spintronic materials with controlled magnetic structure

Abstract

The physical properties of ferromagnetic dilute magnetic semiconductors and nanocomposites are considered in a wide range of temperatures from 5 to 300 K. The latter have several advantages as spintronic materials with a controlled magnetic structure for weak magnetic field sensors. A characteristic feature of ferromagnetic nanocomposites is the spin-dependent tunneling conductance, which is responsible for the negative and positive magnetoresistance. The magnetoresistive effects have a wide range of applications. In particular, materials with such effects may be used in the development of magnetoresistive memory devices, weak magnetic field sensors, medical diagnostic devices, and other items of electronic equipment.

Giant Thermoelectric Power in Co/Al2O3 Ferromagnetic Nanocomposites Below Percolation Threshold

“…Layers of ferromagnetic nanocomposites Co/Al 2 O 3 were grown on planar polycore substrates using electron‐beam facility UE‐142 . The technology is based on two crucible scheme for simultaneous evaporation and condensation of Co and Al 2 O 3 on polycore substrates.…”

“…Earlier we determined the percolation threshold [16] using the dependence of resistivity on the cobalt content in Со/Al 2 O 3 . The percolation threshold for the transition from dielectric to metallic state corresponds to 43 at.% Co. Below this composition Co NP's or their agglomerates do not form electroconductive chains.…”

“…Layers of ferromagnetic nanocomposites Co/Al 2 O 3 were grown on planar polycore substrates using electron-beam facility UE-142. [15,16] The technology is based on two crucible scheme for simultaneous evaporation and condensation of Co and Al 2 O 3 on polycore substrates. The main technological parameters which determine composition and properties of FMNC condensates are the substrate temperature (T s ) and the rates of components evaporation which determine to the condensation speed (V cond ).…”

“…For the sample with concentration of 28.2 at.% (Figure 2a), the M(T) curve has a superparamagnetic character with a blocking temperature about 50 K. For a sample with a large concentration 48.5 at.% (Figure 2b), the superparamagnetic character of M(T) is not observed, which is explained by large dimensions of NP's ($20 nm). [16] Table 1. The main technological growth conditions of Co/Al 2 O 3 FMNC sets.…”

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“…Nanostructured ferromagnetic materials are objects of a considerable interest among researchers [1]. Tremendous attention is being attracted to such materials in recent years due to a wide range of their technological applications including high-density information storage devices [2], magneto-optical sensors [3], spintronics devices [4], biomedical technologies [5] etc, as well as a set of phenomena of fundamental interest such as superparamagnetism [6], giant magnetoresistance [7,8], complicated dynamics of magnetic skyrmions [9] or magnetic catalysis [10]. One of the main and vital parameters which determine the behavior of ferromagnetic materials is the Curie temperature (temperature of a second-order phase transition when magnetic ordering disappears and ferromagnetic materials become paramagnetic).…”