Registration Number
0218U001235,
0113U001672
, R & D reports
Title
The researches of magneto-static, magneto-resonance and magneto-transport properties of magnetic crystals and quantum dimensional structures on their basis.
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Head
Ryabchenko S.M.,
Registration Date
26-01-2018
Organization
Institute of physics NASU
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The magnetoresistance in a group of nanogranular films with different Co contents from 39.5 to 60 m.f. % has been studied in nonconducting Al2On matrices at temperatures 190 ? T ? 300 K. Cubic Co granules had an average size near 6 nm. They, on the average, had an elongated shape in the direction of the normal to the surface of the film, which led to the appearance of a magnetic anisotropy perpendicular to the plane of the film. The granules had a dielectric shell, so that there was no electrical conductivity between them, even when they were contacted by said shells. The threshold of electrical percolation, when the contacts of the granules occurred already with their metal cores, was observed at a Co content of 60 m.f. %. With a larger content, the conductivity of the films in their plane increased sharply. From measurements of magnetostatic properties and magnetic contrast of atomic force microscopy, it is established that samples with a Co content approaching 60 m.f.% are in a superferromagnetic state with a superdomain structure. From measurements of the magnetoresistance at T = 300 K, it was found that for a Co content of 56.5 m.f. % in the dependence of the resistance on the magnetic field, against the background of a general decrease in resistance with an increase in the absolute value of the field, a contribution with a positive magnetoresistance arises, in the vicinity of the small values of field. This contribution occurs only for the presence of a projection of magnetization in the plane of the film. The observed dependences are discussed on the basis of a comparison with the previously developed model of the positive magnetoresistance and its development. For an ensemble of nanogranular single-domain nanoparticles with perpendicular anisotropy, a theoretical calculation of the angular dependence of the coercivity (from the slope of the magnetic field to the anisotropy axis parallel to the normal to the film) is made for the cases of the anisotropy field of the smaller and larger of the maximum possible demagnetization field, which is achieved by directing the magnetic moments of all particles along the normal to the film. The differences from the angular dependences of the stability boundaries of nonequilibrium magnetization of such a film are found. It is established that in the case when the field of perpendicular film anisotropy exceeds the maximum possible demagnetization field, for large deviations of the magnetization direction from the normal to the film, the region of dependence of the magnetization on the external field with an inhomogeneous orientation of the magnetic moments of the granules has parts with a hysteresis-free equilibrium ratio of the amounts of granules magnetized in two different directions and a hysteresis part with a nonequilibrium ratio of these quantities. In this case, at the transition between the indicated parts, the ratio of the number of granules with different moment orientations remains unchanged in a certain interval of magnetic fields. The results can be used to create spintronics devices using films with perpendicular anisotropy, as well as in the development of functional elements based on nanogranular films. In addition, they can be used in the educational process to describe the processes of magnetization reversal of nanogranular films and in the interpretation of the concept of "superferomagnetism" of nanostructures.
Product Description
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Бондар Олександр Васильович
Калита Віктор Михайлович
Кулик Микола Миколаєвич
Лозенко Альберт Федорович
Рябченко Сергій Михайлович
Терлецький Олег Валентинович
Чорноморець Надія Федорівна
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2020-04-02
