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The magneto-Seebeck (MS) effect, which is also called magneto-thermo-power, was observed in Co/Cu/Co and NiFe/Cu/Co spin valves. Their Seebeck coefficients in the parallel state were larger than those in the antiparallel state, and the MS ratio defined as (SAP -SP)/SP could reach –9% in our case. The MS effect originated not only from trivial giant magnetoresistance but also from spin current generated due to spin-polarized thermoelectric conductivity of ferromagnetic materials and subsequent modulation of the spin current by different spin configurations in spin valves. A simple Mott two-channel model reproduced a –11% MS effect for the Co/Cu/Co spin valves, qualitatively consistent with our observations. The MS effect could be applied for simultaneously sensing the temperature gradient and the magnetic field and also be possibly applied to determine spin polarization of thermoelectric conductivity and the Seebeck coefficient of ferromagnetic thin films. [ABSTRACT FROM AUTHOR]

We have calculated magnetostatic fields from transverse and vortex magnetic domain walls in a planar Ni81Fe19 nanowire using micromagnetic simulations. Magnetic fields were calculated either side of the wire in the wire plane. Asymmetries in the stray field from the two types of domain walls can be understood in terms of monopole, dipole and quadrupole contributions. These calculations indicate the required sensitivity of a nearby sensor for domain wall detection or being able to distinguish domain wall character. We demonstrate this by modeling the electrical response of a magnetoresistive multilayer element to a domain wall in a nearby magnetic nanowire. [ABSTRACT FROM AUTHOR]

The optical, magnetic, and transport behaviors of Ge1-xMnxTe (x=0.24 and 0.55) grown by solid-source molecular-beam epitaxy are investigated. X-ray diffraction shows that Ge1-xMnxTe crystallizes in rocksalt structure. The temperature-dependent magnetization (M-T) for x=0.55 sample gives a Curie paramagnetic temperature of θp∼180 K, which is consistent with the temperature-dependent resistivity ρ(T) measurement. Anomalous Hall effect is clearly observed in the samples and can be attributed to extrinsic skew scattering based on the scaling relationship of ρxy∝ρxx1.06. The magnetoresistance of Ge1-xMnxTe is isotropic and displays a clear hysterestic loop at low temperature, which resembles that of giant-magnetoresistance granular system in solids. [ABSTRACT FROM AUTHOR]

We report on magnetic field and temperature-dependent measurements of the anisotropic magnetoresistance (AMR) in epitaxial La1-xSrxMnO3 (LSMO) thin films. While in 3d ferromagnetic alloys increasing the magnetization, either by reducing the temperature or increasing the magnetic field, increases the AMR, we find that in LSMO films the AMR dependence on magnetization displays nonmonotonic behavior which becomes particularly pronounced in lightly doped compounds. We believe that this behavior is related to the inhomogeneity exhibited by these materials. [ABSTRACT FROM AUTHOR]

The interlayer coupling of CoFeB-based synthetic antiferromagnets (SyAFs), modulated by the ion-beam assisted deposition (IBAD) has been systematically investigated under different assisted deposition voltage from 0 to 140 V. We observe that proper IBAD voltage can significantly enhance the antiferromagnetically coupled saturation field from 280 to 1000 Oe and retain the amorphous structure of CoFeB layers. This approach provides a convenient method to enhance the magnetic coupling of SyAFs, which is useful for the magnetic tunnel junctions fabrication and magnetoresistive random access memory development. [ABSTRACT FROM AUTHOR]

Magnetotransport properties of La1-xCaxMnO3 (x=0.33, 0.5) thin films on different substrates are systematically studied. Due to the different lattice-substrate mismatch between films and substrates, compressive, and tensile epitaxial strain can be induced, respectively. The structure distortion induced by the strain with different sign influences the transport property and magnetoresistance. The tensile strain induces an increase of resistivity and magnetoresistance, while the resistivity peak temperature decreases. Compressive strain leads to a contrary behavior. The microstructure of films is also dominated by the lattice-substrate mismatch strongly. The inhomogeneities and different mixed domain structure induce the broadening of magnetic transition in films on SrTiO3 and NdGaO3, and a sharp increase in magnetoresistance in La0.67Ca0.33MnO3 films with increasing field. In addition, the low temperature metal–insulator transition in the resistivity of La0.5Ca0.5MnO3 film on LaAlO3 also indicates the sample inhomogeneities. The suppression of the charge-ordering state in La0.5Ca0.5MnO3 films is mainly dominated by the magnetic field, whereas the effect of the lattice-substrate mismatch is weak. It is due to the origin of the charge-ordering state. When the charge-ordering state is completely suppressed, the effect of lattice-substrate mismatch on charge transport and magnetoresistance shows up obviously. [ABSTRACT FROM AUTHOR]

Oxidation of an AlOx insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 Å thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer. [ABSTRACT FROM AUTHOR]

It has been proposed earlier that the extraordinary magnetoresistance (EMR) observed at room temperature in nonmagnetic semiconducting materials containing metallic inhomogeneities can be used in suitably constructed read heads for magnetic storage devices. Here, we show that such read heads are much simpler in design, and allow for higher sensitivity than is observed using magnetic layered structures that employ the phenomenon of giant magnetoresistance. We calculate, with no adjustable material parameters, the room-temperature response of an EMR read-head design, using finite element analysis, as a function of the position of the magnetic bit relative to the read head. The scaling property of the EMR bodes well for increasing the storage density to 1 Tbit/in.[SUP2] in the near future. [ABSTRACT FROM AUTHOR]

Spin-dependent tunnel junctions, Co/Al[sub 2]O[sub 3]/Co (CoFe)/NiFe, were fabricated to investigate the effect of the additional Co (CoFe) interlayer on tunneling magnetoresistance. The quality of the junction was examined with a cross-sectional image generated by high-resolution transmission electron microscopy, and an electron energy loss spectra map. For junctions with a Co (CoFe) interlayer in the top electrode thinner than 0.8 nm (1.0 nm), the tunneling magnetoresistance ratio increases with interlayer thickness. For junctions with a 0.8–2.0 nm Co (1.0–2.0 nm CoFe) interlayer in the top electrode, the tunneling magnetoresistance ratio reaches the maximum value of 2.16 (4.45) times that without any Co (CoFe) interlayer in the top electrode. The increase in the tunneling magnetoresistance ratio may be attributed to the increased effective ferromagnetic electrode polarization and the various spin-flip scattering factors. [ABSTRACT FROM AUTHOR]

Provides information on a study that observed large negative magnetoresistace in Fe-xCr-10Co alloy thin films prepared by ion beam sputter. Experimental procedure; Results and discussion; Conclusions.

We study the anisotropic magnetoresistance and planar Hall effect of La0.8Sr0.2MnO3 when the field is rotated out of the film plane. We fit the data with a model, which consists of two independent contributions related to (a) the orientation of the magnetization relative to the crystal axes and (b) the orientation of the magnetization relative to the current. We find that the first contribution exhibits a two-fold symmetry, which cannot be explained by the angular dependence of the magnetization magnitude, suggesting an intrinsic source which reflects a deviation from cubic symmetry. [ABSTRACT FROM AUTHOR]

We measured the anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in a [001] oriented epitaxial thin film of La0.7Ca0.3MnO3 (LCMO) as a function of magnetic field, temperature, and current direction relative to the crystal axes. We find that both AMR and PHE in LCMO depend strongly on the current orientation relative to the crystal axes, and we demonstrate the applicability of AMR and PHE equations based on a fourth order magnetoresistance tensor consistent with the film symmetry. [ABSTRACT FROM AUTHOR]

We have performed rf-skin depth (complex-conductivity) and magnetoresistance measurements of antiferromagnetic UTX compounds (T=Ni and X=Al, Ga, Ge) in applied magnetic fields up to 60 T applied parallel to the easy directions. The rf penetration depth was measured by coupling the sample to the inductive element of a resonant tank circuit and then, measuring the shifts in the resonant frequency Δf of the circuit. Shifts in the resonant frequency Δf are known to be proportional to the skin depth of the sample and we find a direct correspondence between the features in Δf and magnetoresistance. Several first-order metamagnetic transitions, which are accompanied by a drastic change in Δf, were observed in these compounds. In general, the complex-conductivity results are consistent with magnetoresistance data. [ABSTRACT FROM AUTHOR]

The low temperature magnetic switching behavior of micron scale NiFe/Cu/Co circular ring elements has been investigated using micromagnetic simulations and magnetoresistance (MR) measurements. The rings were patterned, so that two different contact configurations could be used to measure MR simultaneously. By comparing these measurements with the simulation results, the rings’ magnetization states and switching routes were determined at both 1.7 and 300 K. It was found that at 1.7 K the rings exhibited multiple switching routes and also showed more metastable states and broader transitions between states than was observed at 300 K. The rings’ behavior at low temperature is explained as the result of an increase in the strength of magnetocrystalline and magnetoelastic anisotropies combined with an absence of thermal excitation which would usually aid the nucleation and depinning of domain walls. [ABSTRACT FROM AUTHOR]

Double magnetic tunnel junctions (DMTJs) have been fabricated using alumina barriers with NiFe particles (∼1.8 nm) embedded within. The junctions exhibit spin-dependent transport properties and Coulomb blockade effects. We study differences between control samples and the DMTJs; specifically I-V characteristics and tunnel magnetoresistance (TMR) versus bias voltage characteristics. Clear differences in the systems are evident: the DMTJ with NiFe particles shows a marked peak in TMR at low bias, whereas the dependence of TMR on bias is much weaker for the control MTJ without embedded particles. Hence the TMR at low bias is enhanced by the Coulomb blockade effects. [ABSTRACT FROM AUTHOR]

Annealing is necessary to achieve giant tunneling magnetoresistance (TMR) values in sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). In this study three complementary techniques were used to study the resulting changes in junction microstructure. The as-deposited TMR was modest, 5%, but rose to 101% after annealing at 325 °C for 1 h, corresponding to the tunneling spin polarization rising from 16% to 58%. Soft x-ray resonant magnetic scattering showed a roughening of the magnetic interfaces of the MTJ free layer, confirmed by transmission electron microscopy, which also showed the changes in the CoFeB and MgO to a lattice-matched polycrystalline form. [ABSTRACT FROM AUTHOR]

The magnetization reversal process of MnAs epitaxial films grown on semiconductor substrates was investigated by magneto-optical Kerr effect (MOKE) microscopy, magnetic hysteresis, and magnetoresistance measurements. While the stripe patterns with opposite magnetization in the α-phase of MnAs have been observed previously, we have observed domain dynamics on a vastly different length scale. MOKE images revealed domain nucleation and avalanche domain reversal, which are a collective behavior resulting from interactions among a large number of α-phase regions. The observed reversal processes are reflected in the magnetic hysteresis and magnetotransport measurements. These effects are strongly film thickness dependent. [ABSTRACT FROM AUTHOR]

Tunneling magnetoresistance spectroscopy measurements have been performed on spin-valve magnetic tunnel junctions where the free magnetic electrode is a Cu38Ni62 alloy with a Curie temperature of around 240 K. These measurements allow us to follow the temperature dependence of the energy of the bottom of a minority-spin band close to the Fermi energy, which is partly responsible for the tunneling conductance. The temperature dependence of the tunneling spin polarization of the CuNi electrode has also been extracted using the Julliere formula. We show that the tunneling spin polarization as a function of temperature can be related to the temperature-dependent magnetization using an extension of the commonly applied Stearns model that incorporates the motion of the band close to the Fermi level. This model reproduces the nonlinear relation between tunneling spin polarization and magnetization obtained for Cu38Ni62. [ABSTRACT FROM AUTHOR]

The postdeposition annealing of magnetic tunnel junctions has become standard practice in junction fabrication to improve barrier properties. We have performed tunneling measurements at elevated temperatures during the annealing process on plasma-oxidized, MgO barrier, magnetic tunnel junctions. The data were interpreted in terms of the Hartman model which accounts for an asymmetric barrier profile. The results could not be interpreted solely by the temperature smearing of the Fermi distribution and so the electrode/barrier/electrode structure had been altered during the annealing. While the barrier height at one interface improved, the other was degraded. Our experiments lead us to believe that this is due to the diffusion of Mn to the barrier/pinned electrode interface. We show that through transport and tunneling magnetoresistance measurements it is possible to monitor physical processes such as material migration during the annealing process. [ABSTRACT FROM AUTHOR]

The effects of MgO tunnel barrier thickness on the magnetic-transport characteristics of perpendicularly magnetized magnetic tunnel junction device are explored. Saturation magnetization and initial switching field of the free layer decrease with MgO barrier thickness. Increased MgO thickness that extended interaction distance and diminished the influence from the magnetized pinned layer leads to a smaller initial switching applied field required for saturation. The oscillating dependences of the high coercivity of pinned layer and the low coercivity of free layer on MgO thickness are discovered. Moreover, an out-of-phase feature between both layers’ coercivity cyclic variation is exhibited. This unique cyclic varying of coercivity with MgO barrier thickness is revealed and analogous to the recent finding of the magnetoresistance’s periodic variation with MgO thickness. [ABSTRACT FROM AUTHOR]

The effects of metal-insulator interfacial roughness, modulated by Ar+ irradiation, on bias dependence of tunnel magnetoresistance (TMR) and electrical transport of CoFe–AlOx–CoFe magnetic tunnel junctions (MTJs) have been studied. Reduction of TMR ratio and asymmetric TMR falloff curves as a function of dc bias have been observed for Ar+-irradiated MTJs. The results are analyzed by x-ray reflectivity together with complex impedance techniques, indicating interfacial roughness which likely results in a proportional rising trap state density (TSD). Increasing TSD for Ar+-irradiated MTJs increases an unpolarized current which decreases TMR ratio. The asymmetric TMR falloff curves are attributed to the different TSDs of bottom and top CoFe–AlOx interfaces in tunneling process. [ABSTRACT FROM AUTHOR]

Arrays of micrometer-sized giant magnetoresistance (GMR) magnetic sensors with corresponding micrometer-sized spacing on a single chip are being used to detect very small magnetic fields with high spatial resolution. These very small magnetic fields, or changes in magnetic fields, are associated with magnetic biosensors, nondestructive evaluation, precision position sensing, document validation including currency and magnetic tape, and other magnetic imaging. By using a silicon substrate, the signal conditioning and logic capability of integrated circuits can be incorporated to optimize system performance. This integrated technique reduces the effect of noise and simplifies the sensor/signal-processing interface. GMR sensor arrays with sensor spacing as small as 5 micrometers as well as single-chip arrays with 128 sensors covering a 4 mm width have been constructed. The GMR sensors are made of multilayer material consisting of FeCo/Cu layers with 8% to 20% GMR and maximum sensitivities of 1.0 mV/V/G (100 nV/nT @10 V). The sensor elements are photolithographically patterned with 1.5 to 2 μm wide stripes for high resistance and directional sensitivity. These on-chip magnetic arrays are being applied to various forms of magnetic media as well as work with biosensors and nondestructive test. [ABSTRACT FROM AUTHOR]

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance (MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 °C. The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR. [ABSTRACT FROM AUTHOR]

The role of the density of states in the giant magnetoresistance (GMR) of ferromagnet 1 (FM1)/nonmagnetic (NM=Cu)/ferromagnet 1 (FM1) sandwiches has been investigated by inserting a thin layer of the second ferromagnetic material (FM2=Co) at the FM1/Cu interfaces. As the thickness of the inserted layer increases, the GMR increases to a value seen for purely Co/Cu/Co sandwiches. By using differing FM1 materials [e.g., Py (permalloy (Ni[sub 80]Fe[sub 20]), Ni, Fe] we observe the exponential increase in GMR as more Co is inserted to be dependent on the FM1 material behind it. This is explained by realizing that although the GMR is dominated by the scattering caused by defects like those at the FM2 material/Cu interface, the nature of the scattering depends on the density of states of the FM1 material. This result is discussed in terms of advanced theories on the origin of the GMR in magnetic multilayers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Conventional spin valves consist of two magnetic layers, one of which is pinned by exchange bias to act as a reference magnetic layer in giant magnetoresistance measurements. Antiparallel biased spin valves feature a Co/Ru/Co trilayer in place of this pinned layer, where the Co layers are strongly antiferromagnetically coupled. This leads to hugely enhanced pinning since an applied field will exert opposite torques on the Co layer moments. Spin valves are typically deposited in a magnetic field to define magnetic anisotropies, and the development of magnetic structure in the pinned AF couple is not trivial under these conditions. The resultant moment of the AF couple is found to slowly rotate as the final Co layer is deposited. This results in canted pinning once the exchange bias layer is added. There appears to be some magnetic friction as the Co layers rotate during growth. The rotation means that the pinning direction can take any angle with respect to the growth field, leading to positive or negative (or even orthogonal) exchange bias. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present measurements on hybrid ferromagnetic/semiconductor devices. Single, submicron ferromagnetic structures have been fabricated directly onto the surface of a semiconductor, which incorporates a near-surface two-dimensional electron gas (2DEG). The induced Hall resistance and magnetoresistance of the 2DEG are used to measure the magnetic properties of the stripes directly. The relative merits of these two techniques are compared using a device geometry in which both types of measurement can be made simultaneously. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the oscillatory interlayer magnetic coupling of sputtered iron/neodymium supperlatices. Analysis of the strength of the magnetoresistance oscillations; Experimental methods; Results and discussion.