Nonmagnetic Layer Thickness Research Articles

Negatively charged excitons in semimagnetic CdSe/ZnSe/ZnMnSe quantum dots

Low-temperature (T = 1.6 K) photoluminescence (PL) of individual CdSe/ZnSe/ZnMnSe quantum dots (QDs) with different magnitudes of the sp-d exchange interaction between the magnetic impurity ions and charge carriers has been studied in a magnetic field up to 12 T applied in the Faraday and Voigt geometry. The magnitude of the interaction was controlled by changing the fraction (ηe, h) of the squared wave function of charge carriers in the semimagnetic barrier by means of variation of the nonmagnetic (ZnSe) layer thickness. It is established that the sp-d exchange interaction leads to a change in the sign of the effective hole g factor even for ηe, h ∼ 5%, while further increase in the interaction magnitude is accompanied by a rapid growth in the magnitude of spin splitting for both electrons and holes. The quantum yield of PL exhibits a significant decrease due to nonradiative Auger recombination with the excitation of Mn ions only for ηe, h ∼ 12%, while the rate of the holes spin relaxation starts growing only for still higher ηe, h values. In a strong magnetic field perpendicular to the sample plane, the alignment of Mn spins leads to suppression of the Auger recombination only in the excited spin state. For a small rate of the hole spin relaxation, this leads to a rather unusual result: the emission from an excited trion state predominates in strong magnetic fields.

Tuning the ferromagnetism of one-dimensionalFe∕Pt∕Femultilayer barcode nanowires via the barcode layer effect

Using first-principles density functional theory, we have predicted equilibrium structures and electronic and magnetic properties of one-dimensional ferromagnetic $\mathrm{Fe}∕\mathrm{Pt}∕\mathrm{Fe}$ multilayer barcode nanowires. By increasing the thickness of the Pt layer and consequently reducing the thickness of the Fe layer in the nanowire in the ferromagnetic configuration, we found that the average magnetic moment per iron atom, ${\ensuremath{\mu}}_{av}$, increases monotonically with an $\ensuremath{\sim}1∕N(\mathrm{Fe})$ dependence, where $N(\mathrm{Fe})$ is the number of Fe layers. The monotonic increase in average magnetic moment is attributed to the change in magnetic moment at the Fe-Pt interface, and a simple model is proposed to explain this $\ensuremath{\sim}1∕N(\mathrm{Fe})$ variation of ${\ensuremath{\mu}}_{av}$ in the barcode wires. Modulation of the ferromagnetism based on the number of ferromagnetic and nonmagnetic layer sequences in the nanowire suggests the possible application of these nanowires in nanometer scale magnetic barcodes. Furthermore, analysis of the Kohn-Sham energy bands in barcode nanowires suggests strong dependence of spin-polarized conductance on the nonmagnetic Pt spacer layer thickness, opening up the possibility for their application in magnetoelectronics or spintronics.

Peculiarities of the ferromagnetic resonance in multilayer CoFeZr-α-Si films

The static magnetic properties and ferromagnetic resonance spectra of multilayer CoFeZr-α-Si films with different numbers and thicknesses of magnetic and nonmagnetic layers have been investigated. It is established that the shape of the ferromagnetic resonance spectrum and the resonant fields Hres depend on the thickness of nonmagnetic layers and their total number. The character of changes in the spectrum makes it possible to estimate the quality of layers and interfaces.

Optical and magneto-optical properties of {Co0.45Fe0.45Zr0.1/a-Si}n multilayers

The optical and magneto-optical (MO) properties of {CoFeZr(x)–aSi(y)}n and {CoFeZr(x)–SiO2(y)}n composite films with multilayer structure were investigated. It was shown that the form and magnitude of the MO spectra strongly depend of the magnetic and non-magnetic layer thickness and component of non-magnetic material. The MO spectra were analyzed in the framework of the effective-medium approximations and macroscopic Fresnel magneto-optics to ultrathin layers.

Efficiency of excitation of dimensional resonances of magnetoelastic waves in layered structure

This paper reports the study of elastic and magnetoelastic waves in two-layered structure: magnetic film – non-magnetic substrate, restricted in one dimension. We have investigated behavior of elastic and magnetoelastic standing waves resonant frequencies dependent on the relative thicknesses of magnetic and non-magnetic layers. Magnetic susceptibility of magnetic film placed on non-magnetic substrate and character of its behavior in the vicinity of frequencies of dimensional resonances of magnetoelastic and elastic waves are studied. We have explored susceptibility dependence on the relation between magnetic and non-magnetic layers parameters. By change of the thickness of magnetic layer relative to overall thickness of a sample we can regulate magnetic susceptibility and therefore efficiency of excitation of definite harmonics of standing magnetoelastic and elastic waves. If even number of magnetoelastic half waves falls to magnetic layer corresponding harmonics of magnetoelastic and elastic wave disappears. In particular odd harmonics disappear when magnetic film occupies half space of a sample. Magnetic susceptibilities reveal peculiarities in their behavior dependent on material parameters change.

Chapter 9 Magnetism of multilayer films in transition metal/semiconductor system

In this paper, we present the current status of experimental research in the field of magnetism in multilayer films based on a transition metal/semiconductor system. Exchange interactions are analyzed depending on the technology of film fabrication, materials of different layers, thicknesses of magnetic and non-magnetic layers, temperature, magnetic field, and optical radiation.

Magnetic imaging of layer-by-layer reversal inCo∕Ptmultilayers with perpendicular anisotropy

For very thin Co layers, the exchange coupling between adjacent Co layers in $\mathrm{Co}∕\mathrm{Pt}$ multilayers is ferromagnetic and the coupling strength varies nonmonotonically as the nonmagnetic Pt layer thickness $({t}_{\mathrm{Pt}})$ ranges from $3\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}75\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. We report on the magnetization reversal process in a series of ${[\mathrm{Co}(4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})∕\mathrm{Pt}({t}_{\mathrm{Pt}})]}_{N}$ multilayers observed by magneto-optical Kerr microscopy as a function of ${t}_{\mathrm{Pt}}$ and layer repetition $N$. The images reveal the evolution of magnetic reversal processes that strongly depend on ${t}_{\mathrm{Pt}}$ and therefore on the interlayer coupling. For $\mathrm{Co}∕\mathrm{Pt}$ multilayers with small ${t}_{\mathrm{Pt}}$, e.g., $11\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, where the Co layers are strongly coupled, the whole multilayer switches as a single ferromagnet. As Co layers are separated farther and become weakly coupled, e.g., at ${t}_{\mathrm{Pt}}=41\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, layer-by-layer magnetic reversal is observed. The Kerr images reveal metastable magnetic domain configurations during layer-by-layer switching which is not evident in the measured hysteresis loops during the abrupt magnetic reversal for $\mathrm{Co}∕\mathrm{Pt}$ multilayers with weak interlayer coupling at large ${t}_{\mathrm{Pt}}$.

Magnetization study of interlayer exchange in semiconductor EuS–PbS ferromagnetic wedge multilayers

Interlayer coupling was experimentally studied in semiconductor EuS–PbS ferromagnetic superlattice wedge structures grown on KCl (0 0 1) substrates with the wedges covering the semiconductor nonmagnetic PbS spacer layer thickness from 0.3 to 6 nm. Structural parameters of the wedges were examined by X-ray diffraction analysis of EuS–PbS superlattice period. Measurements of magnetic hysteresis loops of EuS–PbS structures were performed by both SQUID (for small terminal parts of the wedge) and MOKE (magneto-optical analysis along the wedge) magnetometry. A strong decrease of magnetic remanence and an increase of saturation field observed for EuS–PbS structures with the PbS spacer thickness decreasing below about 1.5 nm is discussed in terms of the influence of antiferromagnetic interlayer coupling.

Dimensional resonances of elastic and magnetoelastic vibrations in two layered structure

Peculiarities of dimensional resonances of elastic and magnetoelastic waves in bi-layered insulator structure: ferromagnetic film–non-magnetic elastic substrate have been investigated. Dependences of resonant frequencies of vibration modes upon thicknesses of magnetic and non-magnetic layers, elastic and magnetoelastic parameters, applied magnetic field have been calculated. The presence of peculiarities of resonant frequencies harmonics behavior with change of magnetic layer thickness have been shown.

Surface behavior of La2∕3Ca1∕3MnO3 epitaxial thin films

The role of the surface layers in La2∕3Ca1∕3MnO3 magnetic oxide epitaxial thin films is analyzed. We show that the topmost layers do play a very relevant role on the transport properties acting as an insulating barrier. Atomic force microscopy (AFM) measurements in the current sensing mode exhibit typical features of tunneling conduction. The analysis of the I-V curves by using the Simmons model give values of barrier thickness in good agreement with nonmagnetic layer thickness estimates from magnetic measurements. Ex situ annealing in air at high temperature clearly improve the magnetotransport properties of the films reducing the surface insulating barrier.

Magnetoresistance flipping of Fe∕Ru multilayers prepared by electron-beam evaporation

Fe ∕ Ru multilayers were prepared by electron-beam evaporation. The magnetoresistance (MR) properties of the multilayer switched the MR sign with the Fe and Ru layer thickness. When the thickness of magnetic Fe layers was fixed at 1.2 nm, the MR effects of the multilayer transformed from a negative to a positive one, with the thickness of nonmagnetic Ru layer changed from 1.2 to 5.0 nm. While when the thickness of nonmagnetic Ru layers was fixed, the transformation of the MR effect is inversed, i.e., transformed from a positive to a negative one with the thickness of the magnetic Fe layer increased. The origin of the MR variation is analyzed. The inverse giant magnetoresistance is related to the Fe∕Ru interface layer, in which the scattering spin asymmetry is less than 1. The MR dependence on the Fe and Ru layer thickness reveals the competition between two mechanisms of normal MR and inverse MR

Thickness dependence of interlayer fringe-field coupling in submicrometer NiFe/Cu multilayered pillars

The effect of fringe-field coupling on the magnetization reversal process in submicrometer scale giant magnetoresistive pillars consisting of [NiFe/Cu]/sub 6/ has been investigated by means of current perpendicular to plane magnetoresistance measurements and numerical simulations. The parabolic and reversible magnetoresistance curves due to an opposite rotation of magnetization in neighboring NiFe layers were observed. To explain the field sensitivity of the pillars quantitatively, we have proposed a modified single-domain model, where the magnetic energy of the system is reconstructed using the result of the micromagnetic simulation of a magnetostatically coupled bilayer system. The calculated magnetoresistance curves are consistent with the experimental ones. From the calculated results, the amplitude of the saturation field is found to be proportional to the thickness of the ferromagnetic layer and inversely proportional to the square root of the nonmagnetic layer thickness.

Withdrawal: Dependence of giant magnetoresistance on the thicknesses of magnetic and nonmagnetic layers in dual spin valves [phys. stat. sol. (a) 201, 2995 (2004)]

AbstractThe authors withdraw their article published in phys. stat. sol. (a) 201, 2995 (2004). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dependence of giant magnetoresistance on the thicknesses of magnetic and nonmagnetic layers in dual spin valves

Based on a previous semi-classical model, we investigated the giant magnetoresistance (GMR) as functions of the thicknesses of the outer and center ferromagnetic layers and the nonmagnetic layer in dual spin valves. The calculated GMR was found to be consistent with experimental results, indicating that our model is applicable even for complicated dual spin valve multilayers. Moreover, some theoretical predictions are given in this letter that allow us to propose ways to optimize dual spin valve structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures

The spin-polarized transport is investigated in a new type of magnetic tunnel junctionwhich consists of two ferromagnetic electrodes separated by a magnetic barrier anda nonmagnetic metallic spacer. Based on the transfer matrix method and thenearly-free-electron approximation the dependence of the tunnel magnetoresistance (TMR)and electron-spin polarization on the nonmagnetic layer thickness and the applied biasvoltage are studied theoretically. The TMR and spin polarization show an oscillatorybehaviour as a function of the spacer thickness and the bias voltage. The oscillationsoriginate from the quantum well states in the spacer, while the existence of the magneticbarrier gives rise to a strong spin polarization and high values of the TMR. Our resultsmay be useful for the development of spin electronic devices based on coherenttransport.

DEPENDENCE OF GIANT MAGNETORESISTANCE ON THE THICKNESS OF MAGNETIC AND NON-MAGNETIC LAYERS IN DUAL SPIN VALVES

Based on the previous semi-classical model, we have performed calculation of the giant magnetoresistance (GMR) as a function of the thickness of the top/bottom or center ferromagnetic layers and the non-magnetic layer in dual spin valves. Our results are in good agreement with that reported in experiment, i.e., a GMR maximum is observed when the thickness of the top/bottom magnetic layer is at 20 ~ 40 Å; the GMR value decreases monotonically with the increase of the non-magnetic layer thickness. By considering the "pin-hole" effect, the variation of GMR versus the thickness of the center magnetic layer is also found to be consistent with the experimental result. These calculations will be helpful in the design of high-quality spin-valve structures.

The influence of the top oxide layer and interfacial interdiffusion regions on the polarizing efficiency of FeCoV/TiZr supermirrors

The influence of interdiffusion at the interfaces and oxidation of the topmost layer on the polarizing efficiency of the FeCoV/TiZr supermirror has been studied. It was found out that the thickness of non-magnetic interdiffusion regions is 10±2 A ̊ and the thickness of non-magnetic oxide layer on top of the supermirror is 40±5 A ̊ . In spite of these structural imperfections, the polarizing efficiency of supermirrors is still quite high. The mean polarization of the neutron beam after two reflections from magnetized FeCoV/TiZr supermirrors was found to be no less than 0.9983 within 1.3– 2 A ̊ spectral range.

Magnetoresistance transformation observed in Fe/Mo multilayers prepared by electron beam evaporation

Fe/Mo multilayers were prepared by electron beam evaporation. The magnetoresistance (MR) properties of the multilayers changed significantly with the thickness of Mo layers in the films. When the thickness of nonmagnetic Mo layers reached 3.0 nm, the MR effect of the multilayers transformed from a negative to a positive one. The curve of MR is easily saturated at relatively low applied magnetic fields. The MR ratio of [Fe(1.5 nm)/Mo(1.0 nm)]42 multilayers with a typical negative MR effect can reach an absolute value of 0.1%, and that of [Fe(1.5 nm)/Mo(5.0 nm)]15 multilayers with a typical positive MR effect can reach a value of 0.42%. Antiferromagnetic interlayer coupling can be observed in our films at room temperature. The origin of the MR variation is discussed according to three contributions, i.e. ordinary MR, induced by Lorentz force, anisotropic MR and the MR induced by spin-dependent scattering between the interfaces of the magnetic–nonmagnetic layers.

Inhomogeneous magnetoelastic states and magnetoelastic wave spectrum in a system consisting of magnetic/nonmagnetic multilayers

A study is made of the magnetoelastic (ME) wave spectrum and ME superstructure nucleation in a system consisting of magnetic/nonmagnetic multilayers. A case of rhombic ferromagnetic layers with the hard magnetization axis $\stackrel{\ensuremath{\rightarrow}}{b}$ perpendicular to the layer surface is considered. We show that close to the phase transition associated with the spin reorientation in the layer plane, a ME wave with a horizontal polarization, propagating parallel to the layer plane, becomes unstable. The shear ME wave frequency and group velocity vanish for a finite value of a wave vector, and the wave becomes frozen, forming a ME domain structure localized near the layer interfaces. Existence of a new modulated phase is associated with a ME coupling of the magnetization to lattice deformation on the layer interfaces. The spectra of the surface ME in the homogeneous and modulated phases are calculated. Depending on the magnetic and nonmagnetic layer thickness and temperature, the stability regions of homogeneous collinear $(\stackrel{\ensuremath{\rightarrow}}{M}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{a})$ and angular phases and the ME domain structure are found, where $\stackrel{\ensuremath{\rightarrow}}{M}$ is the magnetization, and $\stackrel{\ensuremath{\rightarrow}}{a}$ is the easy orthorhombic axis direction. The calculation is extended to study the ME wave propagation in the systems consisting of two-sublattice orthoferrite/nonmagnetic multilayers.

Fundamental properties of ferromagnetic micro- and nanostructured semiconductors for optoelectronic application

Magneto-optical methods were applied for investigating the properties of Co/Cu/Co spin-valves deposited on Si substrate. The effects of electron transport and irradiation on remagnetization of such ferromagnetic (spin-valve)/semiconductor structures were studied for various thicknesses of ferromagnetic and non-magnetic layers.