S. A. Matveev

Crystallite-conjugation regions and adjacent lattice regions in polycrystalline iridium: I. Composition and properties of adjacent lattice regions formed in polycrystalline iridium during annealing in an ultrahigh vacuum

In this work, we have studied the characteristics of regions in which atomic probes (APs) 57Co(57Fe) were diffusionally localized in polycrystalline iridium (poly-Ir) using a previously developed method based on Mössbauer spectroscopy. Poly-Ir becomes alloyed with oxygen during annealing even in an ultrahigh vacuum already at a temperature of 0.18Tm (Tm is the melting point of the matrix). After the annealing temperature reaches a certain value, there arises a “compensated” state of lattice regions adjacent to crystallite-conjugation regions (“adjacent zones,” or AZs) in poly-Ir. Such a state of AZs arises due to the mutual compensation of positive relaxation volumes of oxygen atoms and negative relaxation volumes of oxygen-vacancy complexes that are formed during each annealing. Therefore, in the “compensated” state of AZs the isomer shifts δ2 of components 2 of Mössbauer spectra of 57Fe APs become equal to “intrinsic” isomer shifts δintrs, 2 of the Mössbauer spectra of 57Fe APs located in the AZs of impurity-free metals. The “intrinsic” isomer shifts depend parabolically on the charges Z of the matrix-atom nuclei.

Crystallite-conjugation regions and adjacent lattice regions in polycrystalline iridium: II. Composition and properties of cores of crystallite-conjugation regions in polycrystalline iridium during annealing in an ultrahigh vacuum

Composition and properties of cores of crystallite-conjugation regions (CCRs) formed during annealing of polycrystalline iridium (poly-Ir) in an ultrahigh vacuum (UHV) have been studied using the method of intercrystalline diffusion in combination with Mössbauer spectroscopy (ID+MS) that has been developed in our previous works. Upon annealing in a UHV, poly-Ir is doped with oxygen from the atmosphere of the vacuum chamber. Complexes containing two vacancies per oxygen atom are formed in the CCR cores of poly-Ir because of a rearrangement of the atomic structure of the CCR cores upon their doping with oxygen. Using the ID+MS method, we for the first time revealed a “compensated” state of CCR cores in poly-Ir samples annealed in a UHV and of CCR cores in poly-Cr annealed in technical vacuum. The cause of the appearance of “compensated” states in CCR cores is the mutual compensation of relaxation volumes with opposite signs characteristic of different point defects. The relaxation volume of an oxygen atom in the CCR core of poly-Ir is by an order of magnitude greater than that in poly-Cr.

Investigation of nanostructures based on Ni80Fe20/(Ni80Fe20)20Mn80 bilayers with a unidirectional exchange anisotropy

The magnetic properties of nanostructures based on Ni80Fe20/(Ni80Fe20)20Mn80 bilayers have been investigated depending on the thickness of the antiferromagnetic layer and the material of the substrate. The possibility of using the antiferromagnetic alloy (Ni80Fe20)20Mn80 as the material for the pinning layer in spin valves has been considered.

Effect of thermomagnetic treatment on the magnetic properties of permalloy/manganese bilayer films

Formation of unidirectional exchange anisotropy has been studied during thermomagnetic treatment of permalloy-manganese bilayers. It has been found that, starting from the annealing temperature of 230°C, there is observed a shift of the hysteresis loop. The maximum value of the exchange bias field is achieved after annealing at 250°C for two hours and amounts to 155 Oe. Using electron microscopy, it has been demonstrated that the effects of the occurrence of unidirectional exchange anisotropy and of increase in the coercive force are due to the appearance of an ordered antiferromagnetic phase NiFeMn, which is formed as a result of diffusive interaction between permalloy and manganese upon annealing.

Formation of ordered NiFeMn antiferromagnetic phase in permalloy/manganese bilayers in the course of thermomagnetic treatment

The formation of the ordered NiFeMn antiferromagnetic phase in the course of thermomagnetic treatment of manganese-permalloy bilayers has been investigated. The influence of the type of substrate, number of layers, and modes of thermomagnetic treatment on the magnetic properties of the films is studied. It has been shown that the maximal effect of unidirectional anisotropy associated with the presence of the ordered NiFeMn ferromagnetic phase in ferromagnetic layers is attained at an annealing temperature of 260°C for 4 h. The shift in the magnetic hysteresis loop with a thickness of the switched layer of about 40 nm is 380 Oe, while the blocking temperature is ≌270°C.

Mössbauer spectroscopy of interphase boundaries of Co/CoO bilayers

Co films and Co/CoO bilayers that were deposited by the method of magnetron sputtering on the MgO(100) and Al2O3(110) single-crystal substrates have been studied using electron microscopy and Mössbauer spectroscopy. The surface, bulk, and interphase Mössbauer spectra of the layers and bilayers under examination have been investigated. It is shown that the 57Co(57Fe) atoms located in the region of a Co/CoO interphase boundary can be in different magnetic states and have different valences and chemical surroundings.

Study of the possibility of using Ni-Fe-Mn alloys as material for pinning layers in spin valves

Magnetic properties of nanostructures based on Ni80Fe20/(Ni80Fe20)1 − xMnx bilayers are studied at various compositions and thicknesses of the antiferromagnetic (AFM) layer. The possibility of using triple compounds based on Ni-Fe-Mn in spin valves is considered. Regularities of the formation of unidirectional anisotropy in permalloy/manganese bilayers during thermomagnetic treatment are revealed.

Study of YSZ films deposited using electron-beam sputtering onto a nickel alloy with a perfect cube texture

X-ray diffraction analysis and atomic force microscopy were used to study the effect of the state of a substrate (an Ni-11 at % Cr ribbon) and deposition conditions on the texture and roughness of an yttrium-stabilized zirconia (YSZ) buffer layer deposited by electron-beam sputtering. The presence of a sharp cube texture in the nickel-alloy ribbon was shown to be insufficient condition for obtaining a biaxial texture in the YSZ film. A two-dimensional (2 × 2) sulfur superstructure should be formed on the nickel-ribbon surface. In this case, the YSZ film with a sharp {100} 〈100〉 cube texture and surface roughness of ∼10–15 nm can be prepared at a low deposition rate of 0.005–0.008 nm/s and a substrate temperature of 700–800°C.