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

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

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

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

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

Nonlinear absorption and refraction of picosecond and femtosecond pulses in HgTe quantum dot films

We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400–1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were −2.4 × 10−5 cm2 W−1 (in the case of 28 ps, 700 nm probe pulses) and −3 × 10−9 cm2 W−1 (in the case of 28 ps, 400 nm probe pulses), respectively. Our studies show that HgTe quantum dots can be used in different fields e.g., as efficient emitters of high-order harmonics of ultrashort laser pulses or as laser mode-lockers. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Published under the CC BY 4.0 license.European Regional Development Fund (1.1.1.5/19/A/003), Latvian Council of Sciences (lzp-2020/2-0238). Institute of Solid State Physics, University of Latvia as the Center of Excellence acknowledges funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Control of the magnetization orientation in L1<inf>0</inf> FePt films by means of annealing in a magnetic field near the Curie temperature

© 2015, Pleiades Publishing, Ltd. Films of the L10 Fe50Pt50 phase with a thickness of 20 nm in the multilayer Fe(2 nm)/Fe50Pt50(20 nm)/Pt(2 nm) magnetic structure have been prepared by magnetron sputtering. The multilayer structures have been annealed at 700°C for 30 min and then at 430–600°C for 1 h either in an external magnetic field of ∼3500 Oe, which is applied perpendicular to the film plane (the A mode), or without an external magnetic field (the B mode). X-ray diffraction and Mössbauer studies have revealed that the annealing of FePt films in the composition of the multilayer magnetic structure in an external magnetic field at the temperature TC = 478°C (TC is the Curie temperature for FePt films) leads to the formation of the L10 structure with the magnetic moments oriented along the normal to the film surface. In this case, the atomic force microscopy images have demonstrated changes in the grain sizes. When the annealing temperature is close to the Curie temperature TC for FePt films, the thermal perturbation is comparable in magnitude to the magnetization exchange energy; consequently, the external magnetic field of ∼3500 Oe, which is applied perpendicular to the film surface, effectively contributes to the formation of the L10 structure. The annealing of FePt structures in an external magnetic field makes it possible to form the L10 (001) texture in these materials and to orient magnetic moments in the direction of the field

Primordial Nucleosynthesis for the New Cosmology: Determining Uncertainties and Examining Concordance

Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) have a long history together in the standard cosmology. The general concordance between the predicted and observed light element abundances provides a direct probe of the universal baryon density. Recent CMB anisotropy measurements, particularly the observations performed by the WMAP satellite, examine this concordance by independently measuring the cosmic baryon density. Key to this test of concordance is a quantitative understanding of the uncertainties in the BBN light element abundance predictions. These uncertainties are dominated by systematic errors in nuclear cross sections. We critically analyze the cross section data, producing representations that describe this data and its uncertainties, taking into account the correlations among data, and explicitly treating the systematic errors between data sets. Using these updated nuclear inputs, we compute the new BBN abundance predictions, and quantitatively examine their concordance with observations. Depending on what deuterium observations are adopted, one gets the following constraints on the baryon density: OmegaBh^2=0.0229\pm0.0013 or OmegaBh^2 = 0.0216^{+0.0020}_{-0.0021} at 68% confidence, fixing N_{\nu,eff}=3.0. Concerns over systematics in helium and lithium observations limit the confidence constraints based on this data provide. With new nuclear cross section data, light element abundance observations and the ever increasing resolution of the CMB anisotropy, tighter constraints can be placed on nuclear and particle astrophysics. ABRIDGEDComment: 54 pages, 20 figures, 5 tables v2: reflects PRD version minor changes to text and reference