Faraday effect and fragmentation of ferromagnetic layers in multilayer Co/Cu(1 1 1) nanofilms

With purpose to investigate influence of magnetically non-active metal layers on the Faraday effect in multilayer Ferromagnetic/Normal metal films, dependences of the Faraday rotation angles of the light polarization plane on magnetic field have been studied in multilayer [Co/Cu] nanofilms. It was revealed that the Faraday rotation φ varies with thickness of the Cu layers dCu. This φ(dCu) dependence consists of the monotonic component, namely a gradual rise of the angle with increase of dCu, and the non-monotonic one represented by two minima. The monotonic changes of the Faraday rotation were satisfactory described in frames of the effective medium method. Two minima are explained with the Co layer’s fragmentation due to influence of size electron quantization in the Cu layers on formation of Co clusters during deposition of the films.publishe

Magnetic behaviour of perovskite compositions derived from BiFeO3

The phase content and sequence, the crystal structure, and the magnetic properties of perovskite solid solutions of the (1−y)BiFeO3–yBiZn0.5Ti0.5O3 series (0.05 ≤ y ≤ 0.90) synthesized under high pressure have been studied. Two perovskite phases, namely the rhombohedral R3c and the tetragonal P4mm, which correspond to the structural types of the end members, BiFeO3 and BiZn0.5Ti0.5O3, respectively, were revealed in the as-synthesized samples. The rhombohedral and the tetragonal phases were found to coexist in the compositional range of 0.30 ≤ y ≤ 0.90. Magnetic properties of the BiFe1−y [Zn0.5Ti0.5]yO3 ceramics with y < 0.30 were measured as a function of temperature. The obtained compositional variations of the normalized unit-cell volume and the Néel temperature of the BiFe1−y [Zn0.5Ti0.5]yO3 perovskites in the range of their rhombohedral phase were compared with the respective dependences for the BiFe1−yB 3+yO3 perovskites (where B 3+ = Ga, Co, Mn, Cr, and Sc). The role of the high-pressure synthesis in the formation of the antiferromagnetic states different from the modulated cycloidal one characteristic of the parent BiFeO3 is discussed.publishe

Antisymmetric exchange in La-substituted BiFe0.5Sc0.5O3 system: symmetry adapted distortion modes approach

Neutron powder diffraction measurements on the 35 % La-substituted Bi1-xLaxFe0.5Sc0.5O3-composition revealed that the samples obtained under high-pressure (6 GPa) and high-temperature (1500 K) conditions crystalize into a distorted perovskite structure with the orthorhombic Pnma symmetry and the unit cell para-meters: a(0) = 5.6745(2) angstrom, b(0) = 7.9834(3) angstrom and c(0) = 5.6310(2) angstrom. A long-range magnetic ordering takes place below 220 K and implies a G-type magnetic structure with the moments 4.10(4)mu(B) per Fe aligned predominately along the orthorhombic c-axis. The space group representation theory using the orthorhombic symmetry yields four bi-linear coupling schemes for the magnetic order parameters imposed by antisymmetric exchange interactions. The couplings are analysed based on symmetry adapted distortion modes defined in respect of the undistorted cubic perovskite structure. The approach allows a quantitative estimation of the coupling strength. It is shown that the experimentally found spin configuration combines the magnetic order parameters coupled by the atomic displacement modes with the largest amplitudes. The results indicate that the antisymmetric exchange is the dominant anisotropic term which fully controls the direction of the Fe3+ spins in the distorted perovskite lattice

Magnetic phenomena in co-containing layered double hydroxides

Magnetic behavior of CoII(n)AlIII layered double hydroxides (LDHs) (n=Co/Al=2 and 3) intercalated with nitrate was studied as a function of temperature. Both LDH compounds are paramagnetic above about 8K. A rapid increase of their magnetic moments occurs below this temperature until the moments reach the maximum values at Tmax of 4.0K and 3.2K for Co(2)Al-NO3 and Co(3)Al-NO3, respectively. Below Tmax, the zero-field-cooled and the field-cooled static magnetization curves are strongly different. Along with this low-temperature phenomena, Co(2)Al-NO3 and Co(3)Al-NO3 demonstrate anomalous behavior of their temperature dependence magnetic susceptibility in a highertemperature range: between 75 and 175K, both the paramagnetic Curie temperature and the effective magnetic moment change in a non-monotonous way. Possible structural reasons of the observed magnetic behavior of the CoII(n)AlIII LDHs are discussed.publishe

High-power ultrasonic synthesis and magnetic-field-assisted arrangement of nanosized crystallites of cobalt-containing layered double hydroxideu

High-quality stoichiometric Co2Al–NO3 and Co2Al–CO3 layered double hydroxides (LDHs) have been obtained by precipitation followed by anion exchange, both high-power sonication assisted. Application of high-power ultrasound has been demonstrated to result in a considerable acceleration of the crystallization process and the anion-exchange reaction. Two independent approaches were used to form bulk and 2-D samples of Co2Al–NO3 with the oriented crystallites, namely uniaxial pressing of deposits from sonicated LDH slurries and magnetic field assisted arrangement of LDH crystallites precipitating on glass substrates. A convenient way of preparation of semi-transparent compacts with relatively big blocks of oriented crystallites have been demonstrated. Thin dense transparent films of highly-ordered crystallites of Co2Al–NO3 LDH have been produced and characterized.publishe

Phase transitions in the metastable perovskite multiferroics BiCrO3 and BiCr0.9Sc0.1O3: A comparative study

The temperature behavior of the crystal structure as well as dielectric and magnetic properties of the perovskite bismuth chromate ceramics with the 10 mol % Cr3+-to-Sc3+ substitution were studied and compared with those of the unmodified compound. Using a high-pressure synthesis, BiCrO3 and BiCr0.9Sc0.1O3 were obtained as metastable perovskite phases which are monoclinic C2/c with the √6ap × √2ap × √6ap superstructure (where ap is the primitive perovskite unit-cell parameter) under ambient conditions. At room temperature, the unit cell volume of BiCr0.9Sc0.1O3 is ∼1.3% larger than that of BiCrO3. Both perovskites undergo a reversible structural transition into a nonpolar GdFeO3-type phase (orthorhombic Pnma, √2ap × 2ap × √2ap) in the temperature ranges of 410-420 K (BiCrO3) and 470-520 K (BiCr0.9Sc0.1O3) with a relative jump of the primitive perovskite unit cell volume of about -1.6 and -2.0%, respectively. Temperature dependences of the complex dielectric permittivity demonstrate anomalies in the phase transition ranges. The Pnma-to-C2/c crossover in BiCrO3 is accompanied by a decrease in the direct current (dc) conductivity, while in BiCr0.9Sc0.1O3 the conductivity increases. The onset of an antiferromagnetic order in BiCr0.9Sc0.1O3 is observed at the Néel temperature (TN) of about 85 K as compared with TN = 110 K in BiCrO3. In contrast to BiCrO3, which exhibits a spin reorientation at Tsr ∼ 72 K, no such a transition occurs in BiCr0.9Sc0.1O3.publishe

Magnetic-field-assisted deposition of self-assembling crystallite layers of Co2+-containing layered double hydroxides

Precipitation of nanocrystallites of cobalt–aluminium layered double hydroxides in a magnetic field has been studied. In a magnetic field perpendicular to the substrate, dense and homogeneous films have been obtained. Magnetic anisotropy of the crystallites is explained by deviation from the statistical cation distribution in favour of honeycomb-like coordination of cobalt.publishe