Magnetoresistance Of Films Research Articles

Chemical solution deposition and transport properties of La 1− xNa xMnO 3 films on YSZ substrates

Monovalent Na-doped LaMnO 3 films (La 1− x Na x MnO 3) were prepared on single crystal YSZ substrates using chemical solution deposition, which is a low-cost method for large-area film preparation. It was observed that the derived La 1− x Na x MnO 3 films were highly ( h 0 0)-oriented, which was different from the case of previously reported colossal magnetoresistance films on YSZ substrates. The transport properties clearly suggested that the La 1− x Na x MnO 3/YSZ films behaved like epitaxial films, and the relatively large low-field magnetoresistance at 300 K, 5% at 0.5 T, suggest that it would be interesting to further study the Na-doped LaMnO 3 systems.

Chemical solution deposition and transport properties of Ag-doped manganite films

The preparing technique of chemical solution deposition (CSD) for La 0.85Ag 0.15MnO 3 and La 0.85Ag 0.1MnO 3 colossal magnetoresistance (CMR) film is investigated. Polycrystalline-like La 0.85Ag 0.15MnO 3 films are obtained on LaAlO 3 ( h 0 0) and YSZ ( h 0 0) single-crystal substrates as a seed layer is not utilized. However, as a seed layer is used, an epitaxial-like La 0.85Ag 0.1MnO 3 film can be successfully fabricated on LaAlO 3 ( h 0 0) single-crystal substrate. XRD shows that Ag atoms can substitute La atoms without forming any second phases. The magneto-transport property measurement shows that the polycrystalline-like La 0.85Ag 0.15MnO 3 and the epitaxial-like La 0.85Ag 0.10MnO 3 films behave as CMR effect in the whole temperature region below metal–insulator transition ( T p) and in the vicinity of T p, respectively. The results indicate that the CSD method is a worthwhile technique for preparing manganite CMR films with tuning grain orientations.

Optimized Design of Plastic Package for InSb Thin-Film Magneto-Resistance Devices for Gear-Tooth Rotation Detection

This paper discusses the optimized design of the plastic package of Sn-doped InSb thin film magneto-resistance (MR) devices for gear tooth rotation detection. The newly developed package of magneto-resistance elements helps to simplify the assembly of gear-tooth rotation detectors. The properties for detecting rotation and the electrical and operational properties of the new package MR detectors were studied, including the upper limit of operation temperature.

Spinodal induced homogeneous nanostructures in magnetoresistive CoCu granular thin films

A process for producing a dispersion of nanometer-sized, Co-rich particles embedded in a thin film of Cu-rich matrix is presented. Thin films were prepared by thermal evaporation of a bulk CoCu alloys on an amorphous C substrate. In situ transmission electron microscopy (TEM) and field-emission gun TEM equipped with an energy dispersive x-ray spectrometer were used to investigate spinodal decomposition of the initial homogeneous thin film alloy. The maximum giant magnetoresistance (GMR) is found to be 18% for a Co45Cu55 after heating the film from room temperature at 2°C∕minto204°C and holding for 10min. These nanostructures are expected to exhibit optimum GMR for granules having higher Co content.

Interface stability between amorphous ferromagnetic layer and Al oxide barrier in tunneling magnetoresistive films at elevated temperatures

The interface stability and microstructure between amorphous and crystalline ferromagnetic (FM) layers Fe56Co24B20 and Co70Fe30 (at. %) and oxide barrier layers (AlO) deposited by physical vapor deposition, in both as-deposited and annealed states, have been studied using hysteresis loops for magnetic measurement, x-ray photoelectron spectroscopy for elemental depth profiling, and transmission electron microscopy for atomic-level microstructure. AlO was found to be amorphous on both amorphous Fe56Co24B20 and polycrystalline Fe30Co70 FM layers. Substantial Fe diffusion towards the AlO layer and Al diffusion towards the FM layer are clearly observed for the Fe56Co24B20∕AlO system when annealed above 360°C and will likely cause magnetic tunneling junction devices made from this system to fail.

Chemical solution deposition and properties of La0.8Na0.1A0.1MnO3 (A = Ca, Na, Sr) films

Chemical solution deposition as an alternative method for colossal magnetoresistance films is used to prepare the La0.8Na0.1A0.1MnO3 (A = Ca, Na, Sr) on single crystalline LaAlO3 (h00) substrates. The results show that all the derived films are highly (h00)-oriented and have rather large magnetoresistance values near the room temperature. Moreover, for the three films, it is found that the insulator–metal transition temperature (TIM) is higher than that of the paramagnetic–ferromagnetic transition (Tc). It is interesting to find that in the Na-doped manganites the maximum MR value and TIM as well as Tc can be synchronously improved.

Effects of Pt addition on the formation of Co–ITO granular magnetoresistance films by a two-step method

Platinum (Pt) has been added to Co–ITO (ITO: indium tin oxide) films to promote the formation of Co(Pt)–ITO granular structure by a two-step method which includes sputtering deposition at room temperature and postdeposition thermal annealing in a vacuum. Such films consist of magnetic Co(Pt) nanoparticles distributed uniformly in an amorphous ITO matrix. The Co(Pt) particles are formed during the thermal annealing by precipitation, and the matrix also contains certain amount of Co and Pt that suppress the crystallization of the amorphous ITO. Pt plays an important role in controlling the precipitation of Co(Pt) particles and the microstructure formation. First, by adding Pt into the films, more Co can be incorporated into the amorphous phase in the as-deposited state, which ensures sufficient Co to form magnetic particles through precipitation. Second, by incorporating Co and Pt into the film, the crystallization temperature of amorphous ITO is also increased to a temperature as high as 400°C. These two effects make it possible to fabricate the Co(Pt)–ITO granular magnetoresistance films by the two-step method.

Current induced bistability in giant magnetoresistive multilayer thin films

The low frequency noise observed in giant magnetoresistive (GMR) sensors exhibited a bistability at certain critical values of bias current. As the sensor oscillated between the two states of a bistable system, the power spectral density (PSD) of the noise showed two peaks; a narrow low frequency peak corresponding to twice the average residence time in a bistable system and a broad high frequency peak corresponding to intrawell vibration. The peaks were visible in the PSD even when the bistability was not pronounced in a time trace. The PSD showed deviations from a Lorentzian behavior indicating that the energy minima and the barrier between them depended on the bias current. A simple analytic model was developed to describe the change in the energy of the system with bias current. The model was based on the physical structure of the sensor and the estimated path of current flow. At particular current induced bias field values, the system was described by multiple energy minima permitting thermal noise excitation of the free layer magnetization.

Metalorganic chemical vapor deposition of magnetoresistive manganite films exhibiting electric-pulse-induced resistance change effect

The behavior of the film precursors, Pr(DPM)3,Ca(DPM)2, and Mn(DPM)3, in the gas phase was investigated under actual chemical vapor deposition conditions of Pr1−xCaxMnO3. According to in situ infrared absorption spectroscopy, Pr(DPM)3 is much more stable against thermal decomposition than Ca(DPM)2. The atomic composition of the deposited film, such as the Ca∕(Pr+Ca) ratio, can be controlled using the precursor densities obtained by the in situ spectroscopic measurements. The praseodymium manganite films with the appropriate amount of the doped calcium can be deposited without any incorporation of carbon. The composition control on the basis of the in situ monitoring technique is expected to improve the reproducibility of the electrical and magnetic properties of the deposited film.

Ferromagnetic resonance studies on colossal magnetoresistance films: Effects of homogeneity and light illumination

Ferromagnetic resonance (FMR) in the dependence on magnetic field orientation, and effect of the laser light on the magnetic ordering were studied in colossal magnetoresistance films, La1−xSrxMnO3 and La1−xBaxMnO3. The FMR linewidth increased with the decrease in temperature in La1−xSrxMnO3 films, and was nearly temperature independent in La1−xBaxMnO3, that was attributed to the different degree of magnetic homogeneity of the films. Layered structures La1−xBaxMnO3 on silicon with intermediate layer of SrTiO3 were characterized by FMR as highly homogeneous. From the orientation and temperature dependences of the FMR spectra, the effective magnetization, and effective anisotropy fields were estimated. The laser light illumination resulted in the change of FMR line shape and intensity, and was interpreted in terms of optically induced magnetic disordering and effective heating of the spin system.

Co-ITO granular magnetoresistance films fabricated by precipitation of magnetic nanoparticles from amorphous oxide

Abstract

Wet and dry etching of La 0.67(Sr,Ca) 0.33 MnO 3 films on Si

We report etching processes of epitaxial La 0.67(Sr,Ca) 0.33 MnO 3 (LSCMO) colossal magnetoresistive (CMR) films grown on Bi 4Ti 3O 12/CeO 2/YSZ oxide-buffered Si using buffered HF (BHF), potassium hydroxide (KOH) and Ar ion beam etching (IBE) methods. LSCMO films demonstrate high resistivity against the KOH etchant whereas 22 nm/min etching rate was obtained in the BHF with high selectivity over photoresist and Si. Compared to 24 nm/min for Si, Ar IBE yields 16 nm/min etching rate for the LSCMO film and the oxide-buffer layers.

Tuning the inherent magnetoresistance of InSb thin films

We have investigated the 300 K inherent magnetoresistance of undoped InSb epilayers grown on GaAs(001) by molecular-beam epitaxy. The magnetoresistance of these films can be described well using a simplified model that incorporates gradation of properties away from the InSb/GaAs interface and the interplay between conduction and impurity bands. Although there is no significant intrinsic contribution in InSb bulk crystalline (001) materials due to its isotropic Fermi surface and mobility tensor, the linear and quadratic terms in the magnetoresistance as well as the overall magnitude can be tuned by varying the film thickness from 100 to 2000 nm.

Terahertz radiation from magnetoresistive Pr07Ca03MnO3 thin films under strong electric fields

Terahertz (THz) radiation characteristics have been investigated for voltage-biased photoswitching devices (PSDs) coupled with dipole antennas made on magnetoresistive Pr0.7Ca0.3MnO3 thin films. Even under a fixed illumination of femtosecond laser pulses with a power of 14 µJ/cm2, we find the high electric strength in PSDs made on Pr0.7Ca0.3MnO3 thin films in the charge-ordered (CO) state at 10 K. THz radiation linearly enhances with an increase of the biased electric field up to 400 kV/cm without any change of the waveform of the radiated THz pulse. On the other hand, the static time-averaged photoconductance is nearly constant below 200 kV/cm but deviates from it above 200 kV/cm. Such behavior can be ascribed to an increase in the change of the fraction of photogenerated metallic patches within the CO insulating phase. Therefore our findings show that not only Pr0.7Ca0.3MnO3 but also other manganites having a CO state above room temperature may act as efficient THz radiation sources.

Swift ion irradiation induced changes in the structural and transport properties of La 0.7Sr 0.3MnO 3 thin films

Highly c-axis oriented, magnetoresistive thin films of La 0.7Sr 0.3MnO 3 deposited on LaAlO 3(1 0 0) (LAO) substrates by pulsed laser deposition have been subjected to thermal annealing and subsequently to irradiation with swift heavy ions. While the as-deposited films show insulator metal transition T p at ∼265 K, the annealed films show metallic behavior over a wide temperature range viz. from 125 K to 400 K. We have investigated the effect of 90 MeV O 7+ ions and 200 MeV Ag 15+ ions on structural and electrical properties of these films. Dose values ranging from 1 × 10 12 to 1 × 10 14 ions/cm 2 of O 7+ ions and from 1 × 10 11 to 1 × 10 12 ions/cm 2 of Ag 15+ ions were used. The metal–insulator transition reoccurs in the irradiated films and the T p can be tailored to room temperature with irradiation dose value and energy of the ion. Attempt is made to comprehend this variation in T p on the basis of swift ion irradiation induced defects and related strain rather than change in oxygen content of the films.

Production of nanoparticles of different materials by means of ultrashort laser pulses

Ultrashort pulsed laser ablation in vacuum of different targets was performed in order to investigate the possibility of producing nanoparticles with controlled size and shape. A systematic morphology characterization of deposited products was performed for nickel and silicon as a function of laser pulse intensity and wavelength, at a fixed pulse repetition rate. The nanoparticles were investigated by atomic force microscopy, and clear trends for their size and shape anisotropy were evidenced. The best conditions to obtain nanosized particles of oblate ellipsoidal shape, with the minor axis below 10 nm, were determined in the case of nickel targets. Our results show that ultrashort pulse laser deposition can be considered as an interesting technique for the tailoring of nanogranular films with the desired particles dimension and shape, according to the peculiar properties required in specific applications. Moreover, the preliminary features are very promising from the point of view of the production of magnetoresistive films with specific anisotropy.

CPP-GMR with oxidized CoFe layer on various lower-electrode materials

We investigated current perpendicular to the plane-giant magnetoresistive (CPP-GMR) films with a current screen layer of oxidized CoFe. The magnetoresistance (MR) ratio increased monotonically with an increment of resistance-area product (RA) when the thickness of the precursor CoFe layer was increased. We were able to obtain a high MR ratio of 6.7% at an RA of about 2 /spl Omega//spl mu/m/sup 2/. Based on transmission electron microscopic observations, the current screen layer was crystalline, and some metal portions were locally observed in the current screen layer. We also investigated the dependence of CPP-GMR properties on he crystalline structure by changing lower-electrode materials. Decreasing RA without a degradation of MR ratio was observed with increasing grain sizes by changing the lower-electrode materials. Fabricated read heads for perpendicular recording, which had a track-width of 80 nm with an MR ratio of 3% and an RA of 0.6 /spl Omega//spl mu/m/sup 2/, showed a high output voltage of 2.2 mV and a good head-amp signal-to-noise ratio of 30 dB, at an operating voltage of 120 mV. Therefore, an improved CPP-GMR film up to a high MR ratio of 6% at the low RA of 0.3 /spl Omega//spl mu/m/sup 2/ with good soft magnetic properties is promising for future read heads of over 200 Gb/in/sup 2/.

Compositional dependence of magnetoresistance in TbFeCo amorphous film

The dependence of Tb and Co concentration on the magnetoresistance (MR) of TbFeCo amorphous films with perpendicular magnetic anisotropy have been studied at room temperature. Tb/sub x/Fe/sub (88-x-y)/Co/sub y/ films (where x=15--37 at% and y=5--25 at%) with thickness of 200 nm are deposited by dc-magnetron sputtering. The MR ratio is sensitively dependent on the Tb concentration. The MR ratio is increased up to about 2.8% for a Tb concentration of about 22.4 at% then decreased for more Tb content. No significant effect of Co concentration on the MR ratio has been observed. The relation between MR ratio and film composition can be ascribed to the dependence of the domain wall width on the film concentration. The domain wall width decreases with an increase in Tb concentration and again increases for more Tb content showing its minimum value at about 22.4 at % of Tb concentration. It may be considered that the observed MR is contributed from the domain wall.

In situ magnetoresistance measurements of a nanoconstricted nickel-iron film with in-plane configuration

A nanoscale NiFe permalloy point-contact was fabricated in planar configuration on a MgO substrate using an etching process with a horizontal incidence ion beam. In-situ anisotropic magnetoresistance (MR) measurements were successively performed in a vacuum to prevent oxidation. After around 800 seconds of milling, the MR ratio steeply increased to about 2.3% which was much larger than the anisotropic MR ratio of the MR film. In addition, the test-element showed low (high) resistance with parallel (anti-parallel) magnetic geometry of the pinned and free area.

Local structure and electronic properties in colossally magnetoresistive thin film of La0.87Na0.13MnO3 by Mn-K edge EXAFS and XANES

Mn-K edge EXAFS and XANES spectra of La0.87Na0.13MnO3 manganite films with different thicknesses (750, 250, 125 and 50Å), have been acquired at RT. In the 50Å film a shift of the Fermi level downward in energy is found if compared to the other films. In addition, the density of the empty minority spin states is decreased. This finding has been attributed to the presence of some Mn ions experiencing a different local chemical environment that results in the breaking of some DE paths, and in addition to an Anderson localisation of the charge carriers. This last conclusion can explain both the strongly insulating nature and the spin glass like behaviour of the magnetic response of the 50Å film, and has been corroborated by the results of the EXAFS analysis.