Nanostructured Manganite Films Grown by Pulsed Injection MOCVD: Tuning Low- and High-Field Magnetoresistive Properties for Sensors Applications

The results of colossal magnetoresistance (CMR) properties of La0.83Sr0.17Mn1.21O3 (LSMO) films grown by pulsed injection MOCVD technique onto various substrates are presented. The films with thicknesses of 360 nm and 60 nm grown on AT-cut single crystal quartz, polycrystalline Al2O3, and amorphous Si/SiO2 substrates were nanostructured with column-shaped crystallites spread perpendicular to the film plane. It was found that morphology, microstructure, and magnetoresistive properties of the films strongly depend on the substrate used. The low-field MR at low temperatures (25 K) showed twice higher values (−31% at 0.7 T) for LSMO/quartz in comparison to films grown on the other substrates (−15%). This value is high in comparison to results published in literature for manganite films prepared without additional insulating oxides. The high-field MR measured up to 20 T at 80 K was also the highest for LSMO/quartz films (−56%) and demonstrated the highest sensitivity S = 0.28 V/T at B = 0.25 T (voltage supply 2.5 V), which is promising for magnetic sensor applications. It was demonstrated that Mn excess Mn/(La + Sr) = 1.21 increases the metal-insulator transition temperature of the films up to 285 K, allowing the increase in the operation temperature of magnetic sensors up to 363 K. These results allow us to fabricate CMR sensors with predetermined parameters in a wide range of magnetic fields and temperatures.

Блочные и монокристаллические пленки сплава висмут--сурьма 3-12 ат% с подслоем сурьмы

We investigated the effect of the antimony underlayer (10 nm) on the structure and galvanomagnetic properties of bismuth-antimony solid solution thin films (3-12 at.% Sb). The films were obtained on mica substrates by discrete vacuum evaporation and zone recrystallization. We found that the misorientation of the crystallite plane (111) increases relative to the film plane as well as the crystallite sizes decrease. The antimony underlayer does not change the crystallographic orientation during recrystallization and increases the film adhesion. The change in the galvanomagnetic coefficients when using a sublayer is due to the classical dimensional effect and increasing plane deformation.

METHOD OF EXCITATION OF QUASI LONGITUDINAL ACOUSTIC WAVES IN LAYERED STRUCTURES

The analysis of methodological possibilities of excitation of quasi-longitudinal (QL) acoustic waves of the megahertz frequency range in layered structures GaN-on-sapphire is studied and carried out. Volume-type transducers polarized by plate thickness are used to generate and detect QL waves. It is concluded that quasilongitudinal modes (QL) can be excited by this method – the so-called Anisimkin (AN) waves, for which the displacement plane is localized in the film plane and the displacement direction is directed along the wave vector.

Dependence on Film Thickness of Guest-Induced c Perpendicular Orientation in PPO Films

For poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting nanoporous-crystalline (NC) phases, c^ orientation (i.e., crystalline polymer chain axes being preferentially perpendicular to the film plane) is obtained by crystallization of amorphous films, as induced by sorption of suitable low-molecular-mass guest molecules. The occurrence of c^ orientation is relevant for applications of NC PPO films because it markedly increases film transparency as well as guest diffusivity. Surprisingly, we show that the known crystallization procedures lead to c^ oriented thick (50–300 μm) films and to unoriented thin (£20 μm) films. This absence of crystalline phase orientation for thin films is rationalized by fast guest sorption kinetics, which avoid co-crystallization in confined spaces and hence inhibit formation of flat-on lamellae. For thick films exhibiting c^ orientation, sigmoid kinetics of guest sorption and of thickening of PPO films are observed, with inflection points associated with guest-induced film plasticization. Corresponding crystallization kinetics are linear with time and show that co-crystal growth is poorly affected by film plasticization. An additional relevant result of this study is the linear relationship between WAXD crystallinity index and DSC melting enthalpy, which allows evaluation of melting enthalpy of the NC α form of PPO (DHmo = 42 ± 2 J/g).

Spin–orbit torque driven magnetization switching in W/CoFeB/MgO-based type-Y three terminal magnetic tunnel junctions

We have studied current induced magnetization switching in W/CoFeB/MgO based three terminal magnetic tunnel junctions. The switching driven by spin—orbit torque (SOT) is evaluated in the so-called type-Y structure, in which the magnetic easy-axis of the CoFeB layer lies in the film plane and is orthogonal to the current flow. The effective spin Hall angle estimated from the bias field dependence of critical current (Ic) is ~ 0.07. The field and current dependence of the switching probability are studied. The field and DC current induced switching can be described using a model based on thermally assisted magnetization switching. In contrast, the 50 ns long pulse current dependence of the switching probability shows significant deviation from the model, even if contribution from the field-like torque is included. The deviation is particularly evident when the threshold switching current is larger. These results show that conventional thermally assisted magnetization switching model cannot be used to describe SOT induced switching using short current pulses.

Magnetic properties of (Bi1−xLax)(Fe,Co)O3 films fabricated by a pulsed DC reactive sputtering and demonstration of magnetization reversal by electric field

Abstract(Bi1−xLax)(Fe,Co)O3 multiferroic magnetic film were fabricated using pulsed DC (direct current) sputtering technique and demonstrated magnetization reversal by applied electric field. The fabricated (Bi0.41La0.59)(Fe0.75Co0.25)O3 films exhibited hysteresis curves of both ferromagnetic and ferroelectric behavior. The saturated magnetization (Ms) of the multiferroic film was about 70 emu/cm3. The squareness (S) (= remanent magnetization (Mr)/Ms) and coercivity (Hc) of perpendicular to film plane are 0.64 and 4.2 kOe which are larger compared with films in parallel to film plane of 0.5 and 2.5 kOe. The electric and magnetic domain structures of the (Bi0.41La0.59)(Fe0.75Co0.25)O3 film analyzed by electric force microscopy (EFM) and magnetic force microscopy (MFM) were clearly induced with submicron scale by applying a local electric field. This magnetization reversal indicates the future realization of high performance magnetic device with low power consumption.

Exstraordinary and planar Hall effects in thin permalloy films

The Hall resistance hysteresis loops in thin (d = 80 –280 nm) magnetically ordered permalloy films (Ni0.8 Fe0.2) were studied at room temperature at different angles between the film plane and the magnetic field direction (φ = 0 –360°) (extraordinary and ordinary Hall effects), at different angles (θ = 0 – 90°) between the magnetic field direction and the flowing current (planar Hall effect at φ = 0°) in a magnetic field up to B = 1.25 T. The thin films were obtained on sitall dielectric substrate by ion beam sputtering. Sharp peaks of the Hall resistance were observed in the extraordinary and planar Hall effects during the magnetisation reversal of the films due to a change of the magnetisation direction with respect to the sampling current direction. In the extraordinary Hall effect the position and full width at half maximum of a peak is determined by the angle between the magnetic field direction and the film plane. It has been shown that as the direction of the external magnetic field approaches the spontaneous magnetisation direction, both the peak magnetic field position Bp and the full width at half maximum of the peak Δ Bp increase. In the angles range of φ = 0 – 90° Bp and Δ Bp varies in the magnetic field range from Δ В ≈ 0.2 to 5.0 mT. A non-monotonic dependence of the planar Hall resistance and its peak position on the angle between the flowing current and the magnetic field direction was detected. It is related to the change of the longitudinal and transverse components the resistance of the magnetically ordered solids by an external magnetic field. The values of the ordinary and extraordinary Hall effects coefficients have been determined: RH0 = 6 ⋅ 10–9 m3/C and RH1 = 3.2 ⋅ 10–8 m3/C, respectively.

c-Perpendicular Orientation of Poly(ʟ-lactide) Films

Poly(ʟ-lactide) (PLLA) films, even of high thickness, exhibiting co-crystalline and crystalline α phases with their chain axes preferentially perpendicular to the film plane (c⊥ orientation) have been obtained. This c⊥ orientation, unprecedented for PLLA films, can be achieved by the crystallization of amorphous films as induced by low-temperature sorption of molecules being suitable as guests of PLLA co-crystalline forms, such as N,N-dimethylformamide, cyclopentanone or 1,3-dioxolane. This kind of orientation is shown and quantified by two-dimensional wide-angle X-ray diffraction (2D-WAXD) patterns, as taken with the X-ray beam parallel to the film plane (EDGE patterns), which present all the hk0 arcs centered on the meridian. PLLA α-form films, as obtained by low-temperature guest-induced crystallization, also exhibit high transparency, being not far from those of the starting amorphous films.