G. S. Patrin

Crystal structure and magnetic anisotropy of ludwigite Co2FeO2BO3

Co3O2BO3 and Co2FeO2BO3 single crystals with a ludwigite structure are fabricated, and their crystal structure and magnetic properties are studied in detail. Substituted ludwigite Co2FeO2BO3 undergoes two-stage magnetic ordering at the temperatures characteristic of Fe3O2BO3 (TN1 ≈ 110 K, TN2 ≈ 70 K) rather than Co3O2BO3 (TN = 42 K). This effect is explained in terms of preferred occupation of nonequivalent crystallographic positions by iron, which was detected by X-ray diffraction. Both materials exhibit a pronounced uniaxial magnetic anisotropy. Crystallographic direction b is an easy magnetization axis. Upon iron substitution, the cobalt ludwigite acquires a very high magnetic hardness.

Magnetism of Co layers in a Co/Si multilayer film

The magnetic properties of Co/Si multilayer films produced through rf ion sputtering were studied in the temperature range 4.2–300 K. The dependences of the spontaneous magnetization and hysteresis characteristics of the films on the thicknesses of the magnetic layers and nonmagnetic spacers are established. It is shown that these dependences are determined to a large extent by interlayer interfaces, in which the effective magnetic moment of the Co atoms and the exchange interaction decrease and magnetic-anisotropy dispersion arises. A probable cause of the interface formation is interlayer mixing (which is estimated to penetrate to a depth of 15 Å) and the strong effect of Si on the Co electronic structure.

Optically driven conductivity and magnetoresistance in a manganite-based tunnel structure

In the multilayer structure, La0.7Sr0.3MnO3/depleted manganite layer/MnSi, the photovoltaic effect has been discovered. The depleted manganite layer in the structure is dielectric and serves as a potential barrier between the ferromagnetic conducting La0.7Sr0.3MnO3 and MnSi layers by the formation of a magnetic tunnel junction. The photoinduced changes in the transport properties of the magnetic tunnel structure have been observed in the current-in-plane geometry. The changes are reversible and saturate at radiation power densities over 30?mW?cm?2. The photovoltaic effect has a threshold character: it reveals only at h? > 1.17?eV. Most likely, the effect of optical radiation is related to the formation of electron?hole pairs due to interband absorption of light in the dielectric layer. A photocurrent through the tunnel junctions separating the conducting layers causes a redistribution of the current channels between the conducting layers, which influences the conductivity and the magnetoresistance of the structure.

Interface effect on the magnetic properties of Ni-Ge bilayer films

Magnetic and magneto-optical properties of the Ni-Ge bilayer films are studied. The unusual temperature behavior of the magnetization curves is revealed: the hysteresis loops at room temperature have a near-rectangular shape; when the films are cooled down to 4.2 K, the coercive force increases by more than an order of magnitude and the asymmetry and displacement of the loop along the field axis are observed. These effects are stronger in thinner Ni layers. The observed features are attributed to the effect of the interlayer between the Ni and Ge layers, which has a complex magnetic structure.

Spin-glass-like behavior of low field magnetisation in multilayer (Gd/Si/Co/Si)n films

Abstract The results of experimental investigations of magnetic properties of multilayer (Gd/Si/Co/Si) n films in low magnetic fields are represented. The spin-glass-like behavior of magnetization is found. The role of biquadratic exchange coupling in a forming of magnetic state of system is discussed.

Current-driven channel switching and colossal positive magnetoresistance in the manganite-based structure

The transport and magnetotransport properties of a newly fabricated tunnel structure manganite/depletion layer/manganese silicide have been studied in the current-in-plane (CIP) geometry. A manganite depletion layer in the structure forms a potential barrier sandwiched between two conducting layers, one of manganite and the other of manganese silicide. The voltage–current characteristics of the structure are nonlinear due to switching conducting channels from an upper manganite film to a bottom, more conductive MnSi layer with an increase in the current applied to the structure. Bias current assists tunnelling of a carrier across the depletion layer; thus, a low-resistance contact between the current-carrying electrodes and the bottom layer is established. Below 30 K, both conducting layers are in the ferromagnetic state (magnetic tunnel junction), which allows control of the resistance of the tunnel junction and, consequently, switching of the conducting channels by the magnetic field. This provides a fundamentally new mechanism of magnetoresistance (MR) implementation in the magnetic layered structure with CIP geometry. MR of the structure under study depends on the bias current and can reach values greater than 400% in a magnetic field lower than 1 kOe. A positive MR value is related to peculiarities of the spin-polarized electronic structures of manganites and manganese silicides.

Effect of the ferromagnetic layer thickness on the interlayer interaction in Fe/Si/Fe trilayers

Three-layer magnetic film systems Fe/Si/Fe have been studied by the method of magnetic resonance. It is established that the ferromagnetic layer thickness affects the magnitude of the interlayer exchange interaction in this system. A mechanism explaining the observed effect is proposed.

Magnetic properties of Fe/Si/Fe trilayer films

The magnetization of Fe/Si/Fe trilayer films is experimentally investigated at low temperatures. It is found that the shape of the magnetization curves measured at T<30 K depends on the thermomagnetic state of the system. The possible mechanisms of the interaction between iron layers are discussed.

Effect of optical radiation on magnetic resonance in Fe/Si/Fe trilayer films

A photoinduced change in the magnetic resonance parameters is observed in trilayer films of the system Fe/Si/Fe. The shifts of the resonance field and the character of the interlayer interaction are investigated as functions of the temperature, illumination of the films, and thickness of the silicon interlayer. It is found that at low temperatures the photoinduced contribution to the exchange interaction constant between the iron layers is antiferromagnetic.

Antiferromagnetic ordering in REM cobaltite GdCoO 3

Temperature and magnetic-field dependences of the static magnetization of polycrystalline cobaltite GdCoO3 have been measured. The magnetic properties of the GdCoO3 sample have been studied in the paramagnetic and antiferromagnetic states. The magnetic phase diagram has been constructed. The exchange field between the Gd-Gd sublattices and the anisotropy field have been estimated.