B.Z. Rameev

High Curie-temperature ferromagnetism in cobalt-implanted single-crystalline rutile

The ion implantation technique has been used to fabricate a Co-rich layer in rutile: single-crystalline TiO2 substrates were heavily irradiated by Co+ ions with energy of 40?keV. The magnetic properties of as-prepared and post-annealed samples were studied by both inductive and Faraday magnetometry as well as ferromagnetic resonance (FMR). A ferromagnetic Curie temperature as high as 700?K was measured in our samples. The analysis of the magnetic hysteresis loop, the temperature dependence of the saturation magnetization, and strong out-of-plane anisotropy of the FMR spectra allow us to suppose that the origin of the macroscopic high-temperature ferromagnetism is the exchange interaction mediated by oxygen vacancies.

Anisotropy of ferromagnetism in Co-implanted rutile

Magnetic anisotropy of cobalt implanted single-crystalline rutile has been studied by means of magneto-optical Kerr effect (MOKE) and superconducting quantum interference device (SQUID) techniques. We observed for the first time strong angular dependence of the remanent magnetization and coercive field in the plane of the implanted surface: twofold anisotropy for the (100)-substrate and fourfold anisotropy for the (001)-substrate samples. The observation opens up new possibilities to tailor magnetic anisotropies of the material. Possible origins of ferromagnetism and anisotropies in dielectric and diamagnetic single-crystalline TiO2 samples after Co-ion implantation are discussed.

Ferromagnetic resonance in double perovskite epitaxial thin films of La2NiMnO6 on SrTiO3 and NdGaO3 substrates

Ferromagnetic resonance (FMR) studies of epitaxial La2NiMnO6 (LNMO) thin films on (100) oriented SrTiO3 and (110) oriented NdGaO3 substrates at room temperature are presented. Observation of FMR spectra above the Curie temperature of this compound confirms the presence of magnetic ordering in LNMO thin films at room temperature. Best fitting of FMR spectra has been made on the assumption of the coexistence of two magnetic phases with different easy and hard axis periodicities in the film plane of LNMO. The spectra of the films on various substrates are characterized by different in-plane and out-of-plane symmetries, which indicates the existence of different epitaxial growth on the substrates with different crystal symmetries and orientations.

Ion synthesis of iron granular films in polyimide

Abstract 40 keV Fe+ ions were implanted into polyimide (PI) films with doses of (0.25–1.25)×1017 ions/cm2 at ion current densities of 4, 8 and 12 μA/cm2. Transmission electron microscopy study showed that iron granular films consisting of isolated metal particles with lateral sizes of 25–300 nm were formed in the irradiated (carbonised) layer of polymer. An influence of implantation parameters and thermal annealing on magnetic properties of the synthesised iron films was investigated by the ferromagnetic resonance technique. It was found that the metal/polymer composite layer is formed at highest dose of 1.25×1017 ions/cm2 and it reveals the characteristics of a continuous magnetic film: remanent magnetisation and coercive field.

Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001)

Magnetic anisotropies of Co-implanted ZnO (0001) films grown on single-crystalline Al2O3 (112¯0) substrates have been studied by ferromagnetic resonance (FMR) technique for different cobalt implantation doses. The FMR data show that the easy and hard axes have a periodicity of 60° in the film plane, in agreement with the hexagonal structure of the ZnO films. This six-fold in-plane magnetic anisotropy, which is observed for the first time in ZnO-based diluted magnetic semiconductors, is attributed to the substitution of cobalt on Zn sites in the ZnO structure, and a clear indication for long range ferromagnetic ordering between substitutional cobalt ions in the single-crystalline ZnO films.

Ion synthesis and FMR studies of iron and cobalt nanoparticles in polyimides

Polyimide foils were implanted with 40 keV Fe+ and Co- to doses of 0.25-1.5×1017 ions/cm2. Electron microscopy studies showed the formation of iron and cobalt nanoparticles in the implanted polymer layer with a thickness of about 70 nm. The size and shape of the ion-synthesized metal nanoparticles depend on the implantation parameters and subsequent thermal annealing. A ferromagnetic resonance (FMR) response was found in the iron-implanted samples as well as in the annealed cobalt and iron samples. The effective magnetization values of the metal/polymer composite layers were extracted from the FMR spectra and plotted as a function of implantation dose. The magnetic properties of the iron and cobalt nanoparticles in polyimide are compared and discussed.

Ion Beam Synthesis of Magnetic Nanoparticles in Polymers

Different polymers (viscous-flow epoxies, viscoelastic silicone resins and solid state polyimides) were implanted with 40 keV Fe+ or Co+ ions to the doses of 0.1÷2.0×1017 ions/cm2. The influence of the dose and viscosity of polymer target on the process of nucleation and growth of metal nanoparticles in the implanted polymers as well as on the magnetic properties of ion-synthesized composites were investigated by electron microscopy and magnetic resonance. The implantation of the polymers with 40 keV ions causes a surface carbonization of polymer substrate and at the doses more than 0.25×1017 ions/cm2 results in the formation of metal (iron or cobalt) nanophase in thin subsurface layer. Mean sizes, crystalline structure, shape and space packing of the ion-synthesized nanoparticles strongly depend on the dose, kind of implanted ions and the polymer viscosity during implantation. The ion synthesis of the isolated cubic or spherical particles with the mean sizes in the range of 2÷200 nm, as well the formation of many-particles clusters, fractal-type agglomerates and single microscaled plates are observed in the implanted polymers under study. Ion-synthesized iron or cobalt nanoparticles reveal the magnetic resonance response, and at high doses their resonance signals demonstrate the typical features of ferromagnetic resonance in granular magnetic films. The values of magnetization and coercivity of the granular composite films were obtained from the analysis of FMR data. The non-linear dependencies of the composite magnetization on ion dose and on the viscosity of polymer target are presented and discussed in the frame of the magnetic percolation transition in the many-particles system.

Novel approaches in nuclear magnetic/quadrupole resonance techniques for explosives detection

Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) are very prospective methods of the bulk detection of explosives and illicit substances. Both methods are based on use of apparatus, which are very similar technically and in some cases could be applied simultaneously. We report our experimental works on NQR/NMR techniques for explosives detection. In addition of classical single-frequency NMR/NQR we also explored a potential of double resonance (NMR/NQR) and multifrequency NQR approaches as well as magnetic resonance imaging (MRI) techniques. Multifrequency (two/three) NQR technique involves various (two or three) transitions in the three energy level system of 14N nuclei. It is shown that this kind of NQR technique allows filtering spurious signal after radiofrequency pulses and increases the sensitivity of NQR detection. On the other hand, various liquids can be detected using NMR. We shown that reliable discrimination among extended set of liquids reveal a need in use of additional NMR parameters or complimentary techniques. It is demonstrated that MRI is also feasible method for detection of explosive/illicit liquids.

Multiparameter NMR Identification of Liquid Substances

In this paper we study the method of distinguishing the substances by measuring their nuclear paramagnetic longitudinal and transverse relaxation times and the diffusion coefficient of molecules. Experiments performed using a commercial high magnetic field NMR spectrometer show the possibility to use this method for reliable identification of liquids. Observables in these experiments rather often cannot be described by a single exponential function. In the article we discuss how to utilize the non-single exponential experimental dependences for a quantitative processing of the NMR experimental results.

Secondary signals in two-frequency nuclear quadrupole resonance on 14N nuclei with I = 1

Our experimental and theoretical studies show that using two-frequency excitation of (14)N nuclei it is possible to observe secondary NQR signals at one of the three possible transitions due to irradiation of another adjacent transition. As a result of the pulse sequence applied to the adjacent transition the spin-echo signals on the detected transition are observed after essential time interval from the initial single pulse on this frequency. Experiments have been performed on the (14)N nuclei in the sodium nitrite (NaNO(2)) and the military explosive hexahydro-1,3,5-trinitro-s-triazine C(3)H(6)N(6)O(6) (RDX).