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Applications using FeRh for controllable exchange coupling of two magnetic layers with in-plane and out-of-plane anisotropies require ultrathin (~10 nm) films with pure antiferromagnetic (AF) FeRh α" phase at room temperature (RT). However, it is also well known that the antiferromagnetic-ferromagnetic (AF-FM) transition of FeRh is sensitive to composition and deteriorates at low thicknesses. Hence, in this work, we study the composition-dependent phase ordering of co-sputtered FeRh thin films at ultrathin thicknesses of ~10 nm. As the ultrathin films get richer in Rh, the appearance of α" phase is typically characterized magnetically by a sudden drop in RT moment, and structurally by a slight decrease in degree of B2 chemical ordering with a sharp decrease in c-axis lattice constant. These observations are consistent with the FeRh phase diagram where FeRh abruptly enters the AF α" phase once it becomes slightly disordered. Dependences of magnetic transition parameters on composition were also described. Moreover, higher sputtering powers possibly allow the formation of purer α" phase with less γ-face centered cubic phase impurities. Consequently, a composition optimized 10 nm film shows a relatively low residual moment (13.5 emu/cc), thus suggesting good AF phase formation. In addition, correlation of the magnetic transition parameters with the crystal structural parameters reveal that the maximum rate of AF-FM transition (Rmax,h) and the corresponding total change in magnetization (ΔMh) interestingly shows linear dependence on the c-axis lattice constant, but would depart from this linearity under certain conditions, i.e., when grain sizes were large, crystallinity was improved and Fe content was high. [ABSTRACT FROM AUTHOR]

Highly ordered B2 FeRh films with sharp magnetic transitions from the antiferromagnetic (AF) to ferromagnetic (FM) states were prepared on thermally oxidized Si wafers with thicknesses as low as 10 nm. It is found that the transition temperature increases as the thickness decreases from 80 nm to 15 nm, and then decreases from 15 nm to 10 nm. While the ratio of the residual magnetization to the maximum magnetization keeps nearly unchanged for the film thickness of 15 nm and larger, it increases significantly when the thickness is reduced to 10 nm. This residual magnetization was suppressed by slightly increasing the Rh atomic content in 10 nm thick FeRh films. Low-pressure deposition is found to play an important role in the stabilization of the AF phase. By depositing FeRh films at an extremely low pressure of 0.057 Pa, a residual magnetization as small as 13.5 emu/cc at 100 K was observed for a film with a nominal thickness of 10 nm deposited on Si wafer. This value was further reduced to 6 emu/cc when the film is deposited on MgO substrates due to much improved FeRh crystallinity. These results are in close agreement with theoretical predictions on defect and interface induced FM stabilization. [ABSTRACT FROM AUTHOR]

Pseudo spin valves (PSVs) with the structure MgO substrate/L10-Fe50Pt50/TiN/L10-Fe50Pt50 were fabricated with varying TiN spacer thickness from 3 to 7 nm. The giant magnetoresistance (GMR) reached a maximum before diminishing with increasing TiN spacer thickness. The initial enhancement of the GMR was attributed to the reduction in interlayer coupling between the L10-FePt layers. However, a decline in GMR sets in when the current shunting effects negated the enhancement brought about by the improved decoupling. Magnetostatic coupling was the primary source of interlayer coupling in the PSVs. The dependence of interlayer coupling on the remanent state of the hard L10-FePt was also examined based on the magnitude and direction of shift in the center of the minor hysteresis loop. While magnetostatic coupling was present in fully saturated hard L10-FePt, dipolar stray field coupling contributed more significantly to the interlayer coupling strength in partially saturated hard L10-FePt. The stray field coupling strength depended on both the thickness of the spacer and the density of the reversed domains in the hard L10-FePt. [ABSTRACT FROM AUTHOR]

Differential dual spin valves (DDSVs) are a potential candidate for read sensors in ultrahigh density data storage. In this work, we show that the magnetostatic coupling (MC) plays a dominant role in the reversal process of DDSVs at a recording density of 10 Tb/in.2 It has been demonstrated that the conventional bias scheme using a pair of permanent magnet abutted junctions is not suitable in DDSVs due to MC preferring a flux closure configuration between the two free layers (FLs). The unidirectional longitudinal bias field causes the magnetization of the FLs to vary in an asymmetrical way, resulting in undesirable fluctuation when the sensor is subject to a uniform external field. Further studies on the bias field strength revealed that the overall output signal differs in shape and fluctuation magnitude with field. In the differential field test, the MC-induced reversal process was clearly observed, which leads to synchronized magnetization reversal between the two FLs. The single-magnetization transition evaluation shows that DDSV sensors do not respond to the differential fields with a linear dependence, but have an output influenced by the absolute magnitude of the fields. The results presented here are useful for optimization of DDSV sensors for future hard disk recording. [ABSTRACT FROM AUTHOR]

We compared the magnetoresistance (MR) ratios of current-confined-path (CCP) current-perpendicular-to-plane (CPP) giant MR spin valves (SVs) calculated using the two-current-model. The simplified two-current model, which places the parasitic resistance external to the two-current network, has been inaccurate in determining the overall resistance of a SV in parallel magnetization configuration. The characteristics of the error in MR depend on the parasitic resistance value, the spin asymmetry coefficient, and the spacer layer resistivity. In comparison to the complete two-current model, we found that although the simplified model could generally predict the trend of various MR behaviors, it also overestimates MR for different CCP densities. A more comprehensive calculation on the CCP SVs was then performed using the spin-drift-diffusion equations based on the Valet–Fert model. It was found that the MR behavior upon considering spin relaxation in the ferromagnetic layers has a closer match with results predicted by the simplified model due to the strong reduction in spin accumulation in the parasitic layers. Spin relaxation in the spacer layer, however, shows a competing effect that tends to reduce the MR ratios. Our results in this paper are useful for accurate evaluation of MR performance in a CPP SV sensor with current-confined paths. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed to analyze both bulk and interfacial spin depolarization effects on the magnetoresistance (MR) of nanoscale spin valves (SVs). The model is based on the spin coupled Boltzmann transport equations where the momentum spin relaxation arising from spin flip and non-spin-flip scattering are considered. In the boundary conditions we include the parameter q which denotes the interfacial spin flip probability, while bulk spin depolarization is characterized by the ratio r of spin flip to non-spin-flip scattering times. We consider a typical Fe/Cr/Fe pseudo-SV trilayer, and calculate the current for parallel and antiparallel alignments, to deduce the MR. A decreasing trend in MR is observed with an increase in either r or q, with the dependence on q being more pronounced. We also studied the combined effect of interfacial diffusive scattering (described by parameters Ns and D↑) and spin flip scattering. We found that although diffusive scattering generally results in an improvement in MR, this is more than offset by the MR suppression effect arising from spin flip scattering. [ABSTRACT FROM AUTHOR]

Room temperature ferromagnetic Zn0.95Co0.05O thin film with (002) preferential orientation has been deposited by pulsed laser deposition at different substrate temperatures on n-type (100) silicon substrate. A maximum saturation magnetization of 0.86μB/Co was achieved at room temperature. High-resolution transmission electron microscope and x-ray photoelectron spectroscopy results indicate that this ferromagnetism behavior is not due to Co microclusters in the thin film. Zinc interstitials, oxygen vacancies, and lattice defects induced by low substrate deposition temperature show a significant effect on ferromagnetic behavior. By changing the substrate deposition temperature to control the amount of zinc interstitials, oxygen vacancies, and lattice defects, ferromagnetism can be tuned significantly as well, which is a direct evidence that these defects contributed to the ferromagnetism in ZnO:Co thin films. [ABSTRACT FROM AUTHOR]

Thermal magnetization fluctuations in tunneling magnetoresistive heads with track width of ∼100 nm have been studied through high-frequency magnetic noise measurement as a function of both transverse and longitudinal fields. The study suggests that in the dynamic region of the heads, the related power spectral density is determined by the magnetization fluctuations of the free layer. At high fields which drive the sensor to the magnetization saturation, an “abnormal” resonance with substantially high amplitude in comparison with that of the free layer is observed when the magnetization of the free layer is nearly antiparallel to that of the reference layer. This abnormal resonance is excluded from the spin torque effect. The detailed analysis suggests that this resonance is due to the magnetization fluctuations in the reference/pinned layers. [ABSTRACT FROM AUTHOR]

We performed a theoretical study and analysis of the effect of modifying the layer thicknesses of a current-perpendicular-to-plane (CPP) spin valve multilayer on its magnetoresistance (MR) ratio. An increase in the ferromagnetic (FM) layer thickness results in (i) an increase in the spin-dependent component of its total resistance, thereby resulting in higher MR, but also leads to (ii) greater spin relaxation in that layer and (iii) an anomalous MR effect in the high resistance regime, both of which suppress the MR ratio. The interplay of these effects results in a complex MR dependence on FM thickness, instead of the simple monotonic MR increase predicted by the two-current model. It also explains the existence of an optimum FM thickness for maximum MR ratio, as evidenced by experimental data. Finally, we consider the MR dependence on the strength and spin selectivity of interfacial resistances, which can either arise naturally or be engineered in the spin valve structure. The study of the combined effects of the FM layer thickness and resistivity, the MR suppression in the high resistive limit, and the competitive spin-dependent scattering in the bulk and at the interfaces is essential for optimizing the structure and material of a practical CPP spin valve to achieve the maximum MR ratio. [ABSTRACT FROM AUTHOR]

The magnetostriction coefficient (λs) of ultrathin sputtered polycrystalline as-deposited and annealed Ta/Ni81Fe19(t)/Ta films was studied as a function of the thickness. λs and magnetoresistance (MR) of bottom-type spin valves (SVs) with nano-oxide layer (NOL) added in the pinned layer were investigated by using NiFe, Co90Fe10, and CoFe/NiFe/CoFe layers as free layer (FL), respectively. λs of SV with NOL increased slightly except that of CoFe FL. NOLs were added at different positions to study the effects of NOL on λs of CoFe FL. All λs of CoFe FL change from negative to positive and its absolute value also increases significantly with CoFeOx related NOL added below. Our λs and surface roughness results indicated that the structure of the film not the roughness dominates λs of ultrathin FL in SVs. [ABSTRACT FROM AUTHOR]

Magnetization properties of magnetic nanowire arrays are studied on various ferromagnetic materials grown in anodic alumina (alumite) and track etched polycarbonate (PCTE) membranes by pulsed electrodeposition. Magnetization curves were measured as functions of wire material, field orientation, and wire length. The coercivity (H[sub c]) and remanent squareness (S) of the various wire arrays were derived from hysteresis loops as a function of angle (θ) between the field and wire axis. For PCTE membranes, H[sub c](θ) curves for CoNiFe, NiFe, and Co nanowire arrays all show an otherwise-bell-type variation, while they change shapes from the otherwise bell to bell type for Ni nanowire arrays as the wire diameter decreases to 30 nm. These characteristics can be understood based on different magnetization reversal mechanisms of small wires. The effect of magnetostatic interaction among wires on the magnetic properties was examined by changing the wire lengths in alumite membranes. It is found that the interaction reduces H[sub c] and S values significantly and may cause the overall easy axis change from parallel to perpendicular to the wire axis. However, the interaction is much weaker than expected from an independent precession theory. The strong coupling among the wire may also induce a change of magnetization reversal mechanism. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the measurement of the magnetoresistance curves of a silver-clad bismuth tape below critical temperature over a magnetic field range up to 8 T. Method used to fabricate the samples with nominal composition; Expressions for a constant magnetic field and an isothermal magnetoresistance curve.

Presents detailed measurements of voltage-current curves and magnetoresistance for bismuth thick film. Discussion on the magnetic properties of superconductors; Use of magnetoresistance; Information on the voltage-current characteristics for bismuth silver clamped thick film at various temperatures.

Field dependence of low frequency noise in tunnel magnetoresistance (TMR) heads with different barrier materials of TiO2, Al2O3, and MgO has been studied. It is found that for MgO-TMR heads, the noise amplitude increases as the sensor is driven from parallel to antiparallel magnetization configurations. However, this field dependence of the noise is not magnetic in origin and can be accounted for by the coherent tunneling mechanism in MgO-TMR heads. For TiO2- and Al2O3- TMR heads, low frequency noise is generally independent of magnetic field when the heads are biased properly by hard bias. A noise spike related to a resistance jump in the transfer curve is measured in a head without proper hard bias. Field-dependent low frequency noise is observed for TMR heads without hard bias. The noise amplitude follows the sensitivity function of the sensor and can be attributed to the thermally activated magnetization fluctuations. Spin transfer (ST) effect on low frequency noise was examined by noise measurements of field dependence at different current directions. Extra noise appears when the TMR head is in antiparallel magnetization configurations. The results suggest that the ST-induced extra noise can be either pure 1 / f noise or the combination of both 1 / f and random telegraph noises. [ABSTRACT FROM AUTHOR]

Two series of Co2MnAl (CMA) and Co2MnAlO (CMAO) thin films deposited on Si (100) coated with thermo-SiO2 by using two CoMnAl targets were studied. One target is oxygen-free and the other one contains 0.8% oxygen. The properties of the two series CMA (O) films strongly depend on deposition conditions and seed layers. The oxygen impurity is a key factor to influence the properties. It would obviously increase the thickness of magnetic dead layer, weaken the magnetic anisotropy, and significantly decrease the spin polarization in CMA film. The magnetoresistance ratios of IrMn pinned top-type magnetic tunnel junctions by utilizing CMAO/CMA as the bottom ferromagnetic electrode were 19% and 68%, respectively. [ABSTRACT FROM AUTHOR]

A series of polycrystalline full-Heusler Co2MnAl thin films were deposited on Si (100) coated with thermo SiO2 by using different types of seed layers such as Cr, Mg, MgO/Cr, and MgO. The properties of the Co2MnAl thin films such as the coercivity, atomic composition, and crystalline structure strongly depend on the deposition conditions and seed layers. Very soft Co2MnAl thin films with coercivity of 8.3 Oe and small magnetostriction coefficient λS=1.43×10-5 had been obtained when MgO was used as seed layer. Magnetic tunnel junctions with magnetoresistance ratio of 12%–19% by utilizing the Co2MnAl as bottom ferromagnetic electrode have been successfully fabricated. [ABSTRACT FROM AUTHOR]

The peak value (PSDp) from power spectral density (PSD) curves was obtained as a function of burning current before and after the breakdown in tunnel magnetoresistive (TMR) heads. The obtained PSDp versus current curves can be classified into two categories. For one set of TMR heads, an abnormal peak was observed just before the breakdown of TMR heads. For another set of TMR heads, PSDp shows a nearly linear current dependence as expected from the mag-noise theory. After the pinhole growth, the abnormal PSDp peak disappears, implying that it is related to the pinhole-free barrier. Spin transfer effect was examined to understand the abnormal increases in PSDp by both reversing current direction and reducing measuring current. The result shows that the spin transfer effect is not important for the presence of the abnormal increase in PSDp. In spite of the lack of a full understanding, we will give discussions on possible mechanisms. [ABSTRACT FROM AUTHOR]

A spin valve magnetoresistive random access memory with a flux-closed structure is presented. The flux-closed structure prevents the disruption to magnetization of the recording layer and increases the thermal stability. Simulation results show that the switching field increases under the uniform external field, however, the switching field has no change under the bit current field. Only the bit current that flows mostly at the center is used to switch the cell. Experimental results show that the bit current of 10 mA is sufficient to switch the 1 μm × 4 μm cell. [ABSTRACT FROM AUTHOR]