Dependence of the microstructure and magnetic properties of amorphous TbFeCo films on the type and pressure of the gas in sputtering

Amorphous Tb30Fe60Co10 films have been fabricated by magnetron sputtering. The dependences of the microstructure and magnetic properties of these films on the type and pressure of the gas in the sputtering chamber have been studied. The pressure of the Ar, Kr, and Xe gases used in the experiments is varied in the sputtering chamber from 0.01 to 4.00 Pa. It has been established that sputtering in the heavy gas (Kr) conducted within the pressure range covered does not permit fabricating TbFeCo films with the easy magnetization axis perpendicular to the film plane. With Xe used at pressures below 1.0 Pa, one observes in TbFeCo films an increase of the coercivity, with the hysteresis loop approaching rectangular shape. Sputtering and deposition in Ar at a pressure of ~0.67 Pa result in the formation of amorphous Tb30Fe60Co10 films with magnetic characteristics satisfying the requirements imposed upon information carriers intended to be employed in perpendicular recording. It has been demonstrated that, by magnetron sputtering in an Ar atmosphere performed at pressures below 1 Pa, one can produce amorphous Tb30Fe60Co10 films suitable for magneto-optical ultra-high-density information recording. © 2012 Pleiades Publishing, Ltd

A study of the properties of core/shell/shell Ag/FeCo/Ag nanoparticles

© 2017, Pleiades Publishing, Ltd. The properties of heterophase core/shell/shell Ag/FeCo/Ag nanoparticles synthesized via a plasma method that are promising for biological applications are studied. As is established, the core/shell/shell Ag/FeCo/Ag nanoparticles exhibit a superparamagnetic state at room temperature that allows one to manage the hyperthermia process. The magnetic characteristics of core/shell/shell Ag/FeCo/Ag nanoparticles are interpreted by assuming partial oxidation of the surface layer of a ferromagnetic FeCo shell and formation of the antiferromagnetic Co x Fe 1–x О layer on the FeCo surface. The interaction between the surface antiferromagnetic Co x Fe 1–x О layer and the ferromagnetic FeCо shell causes the emergence of the exchange bias in Ag/FeCo/Ag nanoparticles

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© 2017, Pleiades Publishing, Ltd. The properties of heterophase core/shell/shell Ag/FeCo/Ag nanoparticles synthesized via a plasma method that are promising for biological applications are studied. As is established, the core/shell/shell Ag/FeCo/Ag nanoparticles exhibit a superparamagnetic state at room temperature that allows one to manage the hyperthermia process. The magnetic characteristics of core/shell/shell Ag/FeCo/Ag nanoparticles are interpreted by assuming partial oxidation of the surface layer of a ferromagnetic FeCo shell and formation of the antiferromagnetic Co x Fe 1–x О layer on the FeCo surface. The interaction between the surface antiferromagnetic Co x Fe 1–x О layer and the ferromagnetic FeCо shell causes the emergence of the exchange bias in Ag/FeCo/Ag nanoparticles

Effect of annealing in an external magnetic field on the microstructure and magnetic properties of the Fe/FePt/Pt multilayer system

The effect of annealing in an external magnetic field applied perpendicular to the plane of the film on the kinetics of Ll 0 phase transformation of the microstructure and the magnetic properties of the Fe(2 nm)/FePt(20 nm)/Pt(2 nm) multilayer system has been investigated. The relations between the hysteresis loop shape, magnetic correlation length, and structural disorders, which are characteristic of magnetic information carriers, have been analyzed. It has been found that the annealing of the Fe(2 nm)/FePt(20 nm)/Pt(2 nm) multilayer system at a temperature of 470°C in an external magnetic field of 3500 Oe, which is applied perpendicular to the film plane, leads to the formation of a face-centered tetragonal structure of the Ll 0 phase in the FePt film, which is characterized by the high coercivity H c, the (001) preferred texture, the magnetic anisotropy perpendicular to the film plane, small sizes of FePt grains in the film, and weak exchange coupling between the particles. The energy of the external magnetic field encourages the process of transformation of the FePt film into the Ll 0 phase. Thus, a method has been developed for fabricating multilayer films based on the FePt Ll 0 phase with the parameters necessary for information carrier materials with perpendicular-type magnetic recording. © 2012 Pleiades Publishing, Ltd

Microstructure and magnetic properties of multilayered [Fe/Pt]n structures prepared by successive deposition

The structure and magnetic properties of multilayered [Fe/Pt]n structures prepared by successive magnetron sputtering of Fe and Pt plates and deposition of Fe and Pt layers on a preliminarily heated glass substrate have been studied as functions of the number n and thickness of the layers. Mössbauer studies and measurements of magnetic hysteresis loops (MH) have established that [Fe/Pt]n films for n = 16 exhibit primarily magnetic anisotropy normal to the film plane. Data obtained by X-ray photoelectron spectroscopy (XPS) strongly suggest that the films have an interface between the substrate and the multilayered structure. Our micromagnetic modeling leads to the conclusion that the magnetic anisotropy oriented normal to the [Fe/Pt]n film plane (for n = 16) is induced by formation of an anisotropic interface. © 2013 Pleiades Publishing, Ltd

Effect of the CrW sublayer on the structure and magnetic properties of thin FePt films

Multilayer Fe 55Pt 45(20 nm)/Pt(5 nm)/Cr 100 - xW x(80 nm)/glass structures, in which the Fe 55Pt 45 magnetic film has a face-centered tetragonal (FCT) structure of the L1 0 phase with the (001) texture, have been prepared using magnetron sputtering. The microstructure and texture of the FePt films have been studied as functions of the W content in the Cr 100 - xW x sublayer, where 0 < x < 25. It has been established that an increase in the W ion concentration leads to the formation of the (200) texture in the Cr 100 - x sublayer and to an increase in the Cr lattice constant. This is accompanied by a decrease in the temperature at which the facecentered cubic phase transforms into the FCT phase of the FePt films as a result of the increase in tensile stresses along the a axis. It has been found that the coercivity of FePt films deposited on CrW substrates increases with increasing W content in the Cr 100 - xW x sublayer because the CrW alloy thus formed precludes diffusion between the FePt film and the CrW sublayer. An additional 5-nm-thick intermediate Pt layer is also deposited to suppress diffusion between the FePt and CrW layers. As a result, the highly textured FePt(001) films intended for ultra-high density magnetic information recording are deposited on a substrate heated to a temperature of 400°C and the Cr 85W1 15 sublayer. © 2012 Pleiades Publishing, Ltd

Magnetic anisotropy of multilayer [Fe/Pt]n structures

The possibility of controlling the magnetic anisotropy of multilayer [Fe/Pt]n structures grown by magnetron sputtering of Fe and Pt plates by varying number n of layers is studied. Mössbauer spectroscopy data and measured magnetic hysteresis loops demonstrate that the multilayer [Fe/Pt]n structures at n = 16 have a predominantly perpendicular magnetic anisotropy. The results of X-ray photoelectron spectroscopy and micromagnetic simulation point to the presence of intermediate layers enriched in iron ions in the structures. The magnetic anisotropy perpendicular to the surface of the [Fe/Pt]n films at n = 16 is found to be caused by the anisotropy of the intermediate layers. © 2014 Pleiades Publishing, Ltd

Mössbauer studies of structural properties and electrochemical characteristics of LiFePO 4

The valency state and local coordination of Fe ions of four industrial samples and a sample of cathodic materials for recharcheable lithium ion batteries obtained using an original technology of St. Petersburg State Technological Institute (Technological University) were studied using the Mössbauer effect on the 57Fe isotope. It was found that the main valency state for more than 90% of iron ions was Fe 2+. The values of isomer shift δ = 0.96-0.98 mm/s and quadrupole splitting σ = 2.88-2.93 mm/s for Fe 2+ ions coincide with the values for compounds with the structure of olivine LiFePO 4 and occupy positions in highly distorted FeO 6 octahedrons. Fe 3+ ions are in octahedral and/or tetrahedral local positions. © 2012 Pleiades Publishing, Ltd

Magnetic and Mössbauer studies of L1<inf>0</inf>–FePt/Fe/Ta multilayer structures

© 2017, Pleiades Publishing, Ltd.Magnetic L10–FePt(10 nm)/Fe(t, nm)/Ta(2 nm) (t is the Fe film thickness that is varied from 0 to 15 nm) multilayer structures have been prepared by magnetron codeposition. The 2-nm-thick Ta layer is a corrosion protection. The magnetization reversal processes and the magnetic interactions have been studied. The hysteresis loops measured in the plane of a single-layer L10–FePt films demonstrate a near-linear behavior. N the magnetic multilayer FePt(10 nm)/Fe(t, nm)/Ta(2 nm) system, in which the Fe layer thickness is smaller than 3 nm, the FePt/Fe system behaves as a single-phase magnetic material and the coercivity is close to the values determined by the Zeeman energy. In the case when the Fe layer thickness in the magnetic multilayer FePt(10 nm)/Fe(t, nm)/Ta(2 nm) structure is larger than 3 nm, the hysteresis loops measured in the structure plane indicate that the FePt/Fe film possesses the properties analogous to the properties of a soft magnetic material. The Mössbauer studies showed that the minimal deviation of the magnetic moments on the normal to the multilayer structure surface was observed as the Fe layer thickness is 1 nm. The increase in the Fe layer thickness to values higher than 1 nm led to the increase in the angle of deflection θ to ~40° at t = 15 nm. In this case, the coercivity of the multilayer structure slowly decreased, because of the limitations of the exchange bond length between the FePt and Fe layers. The measured values of the coercivity were optimized using relationship 1/tFe1.15

Influence of the film thickness and additional elements (Al, O, and N) on the properties of FeCo film structures

The magnetic properties and domain structure of FeCoAlON thin films with thicknesses varying from 55 to 550 nm have been studied, and conditions favoring preparation of FeCoAlON films with uniaxial anisotropy in the direction normal to the film plane, which is required for designing "perpendicular" super-high-density information recording, have been established. In FeCoAlON films with a thickness up to 300 nm, the domain structure consists of cross-linked domain walls, because strong demagnetizing field suppresses formation of stripe domains. After the film thickness has reached 320 nm, cross-linked domain walls transform into stripe domains, with uniaxial anisotropy in the film plane disappearing, to become replaced by uniaxial anisotropy in the direction normal to the film plane, which can be assigned to magnetoelastic stresses induced by nitrogen atoms filling up interstitial space in the (110) plane. A further increase in the film thickness (up to 550 nm) leads to a rotational anisotropy due to the increase of nitrogen concentration in interstitials and the increase of magnetoelastic stresses. © 2014 Pleiades Publishing, Ltd