Reversal of the Pinning Direction in the Synthetic Spin Valve with a NiFeCr Seed Layer (original) (raw)
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Applied Physics …, 2009
We report an oscillation of the giant magnetoresistance ͑GMR͒ ratio as a function of Ru layer thickness in the CoFe/Cu/͓CoFe/Ru/CoFe͔SAF/Cu/CoFe/IrMn dual spin valve ͑SV͒ structure. A normal GMR with a positive sign is observed for the thickness of Ru providing a ferromagnetic interlayer exchange coupling ͑IEC͒. The inverted GMR is observed for the thickness of Ru providing an antiferromagnetic IEC, which is consistent with IEC period across the Ru spacer as well as the electrical separation of the overall structure into two SVs connected in parallel.
Magnetic properties of uniaxial synthetic antiferromagnets for spin-valve applications
Physical Review B, 2005
The magnetic properties of synthetic antiferromagnetic Si͑100͒ /Ta ͑5 nm͒ /Co͑t 1 ͒ / Ru ͑0.65 nm͒ /Co͑t 2 ͒ /Ta ͑10 nm͒ with an obliquely sputtered Ta underlayer are reported as a function of the top Co layer thickness, t 2 . The morphological origin of the large in-plane magnetic anisotropy created by the obliquely sputtered Ta underlayer is revealed by atomic force microscopy. The magnetic anisotropy of the base Co layer is determined by measuring the dispersion of the Damon-Eshbach spin-wave mode with Brillouin light scattering. Ferromagnetic resonance measurements and hysteresis loops reveal that both the anisotropy and the saturation field of the trilayer system decrease with increasing top Co layer thickness. The dependence of the saturation field on layer thickness is fitted to an energy minimization equation that contains both bilinear and biquadratic exchange coupling constants. Magnetoresistance and polarized neutron reflectometry results both confirm that the magnetic reversal process of the system is through magnetic domain formation followed by rotation.
2020
A giant magnetoresistance (GMR) multilayer spin-valve stack was investigated utilizing X-ray diffraction (XRD), reflectivity (XRR) and cross-section transmission electron microscopy (XTEM). X-ray reflectivity analysis indicated that layer thickness and density values were within 10% percent of the nominal values with the exception of CoFe and Cu layers, both of which possessed lower than nominal thickness and density. Interface roughness/interdiffusion increased progressively from the substrate (2 A) to the surface (20 A) of the samples, especially with the addition of the antiferromagnetic NiMn layer. The top Ta layer possessed a thin (20 A), low-density oxide and the buried Ta/NiFe interface was deemed to be associated with a thin (18 A) low density Ta layer at the interface. X-ray diffraction analysis showed that the NiFe/CoFe/Cu/CoFe layers possess a single, sharp ( 11 l}fcc/(OO2)hcp fiber texture. A complex structural evolution was found to be associated with deposition of the ...
… , IEEE Transactions on, 2009
Giant magnetoresistance (GMR) in spin valves is due to spin-dependent scattering occurring at ferromagnet/normal metal (F/N) interfaces and/or in the ferromagnetic layers. In a spin valve with a typical F/N/F structure where the spin scattering asymmetry factor (alpha) of both F/N interfaces is the same (more or less than 1), the GMR is expected to be positive. If alpha is greater than one at one F/N interface and less than one at the other F/N interface, however, the GMR is expected to be negative. Here, we show that the F1/Cu/SAF/Cu/F2/IrMn dual spin valve structure exhibits negative GMR, where F1 and F2 are CoFe and SAF = CoFe/Ru t/CoFe, due to both opposite electron spin scattering asymmetry factor at the CoFe/Ru/CoFe interfaces as well as the electrical separation of the overall structure into two GMR spin valves connected in parallel. A GMR of 6% is observed in the structure without the Ru spacer layer, insertion of a 0.6 nm thick Ru in the SAF results in a negative GMR ratio of -3% , which becomes positive again at the Ru thickness of 0.8 nm, the oscillation from positive to negative MR is consistent with interlayer exchange coupling period across the Ru spacer.
Dual behavior of antiferromagnetic uncompensated spins in NiFe/IrMn exchange biased bilayers
Physical Review B, 2010
We present a comprehensive study of the exchange bias effect in a model system. Through numerical analysis of the exchange bias and coercive fields as a function of the antiferromagnetic layer thickness we deduce the absolute value of the averaged anisotropy constant of the antiferromagnet. We show that the anisotropy of IrMn exhibits a finite size effect as a function of thickness. The interfacial spin disorder involved in the data analysis is further supported by the observation of the dual behavior of the interfacial uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we have observed that the antiferromagnetic uncompensated spins are dominantly frozen with nearly no rotating spins due to the chemical intermixing, which correlates to the inferred mechanism for the exchange bias. PACS numbers: 75.60.Jk, 75.70.Cn, 61.12.Ha The tremendous advances of spintronics research initiated by the discovery of interlayer exchange coupling [1] and giant magnetoresistance [2, 3] uses extensively the exchange bias (EB) effect to control the magnetization of ferromagnetic components. This is a consequence of the direct exchange at the interface between feromagnetic and antifereomagnetic layers and/or nanoscale heterostructures which causes a shift and a broadening of the hysteresis loop of the ferromagnet. This effect which was engineered by nature a few billion years ago [4], was experimentally discovered 60 years ago by Meiklejohn and Bean (M&B) [5] when studying Co particles embedded in their natural oxide (CoO) matrix. Extensive experimental and theoretical studies of the EB effect provide now sufficient understanding for utilizing it as a probe for further fundamental research .
IEEE Transactions on Magnetics, 2000
We present a study of the dependence of Cu spacer interlayer coupling field ( coupl ) on the thickness of the Cu and the deposition rate of the layers in spin valves (SVs). We considered two series of SVs made of NiFe/CoFe/Cu/CoFe/MnIr with Cu ranging from 16 to 26 A. In series 1, the deposition rates were 0.49 A s for Cu and 0.29 A s for CoFe. In series 2, the deposition rates were lower: 0.28 A s for Cu and 0.23 A s for CoFe. We found that lowering the deposition rates led to considerably lower coupl ; about 24 Oe in series 1 versus about 13 Oe in series 2, both with = 19 A and temperature = 300 K. In both series, we observed an increase of coupl when is reduced (as would be expected from Néel coupling dominance). The increase is weaker in the low deposition rate series. The difference is related to the different roughness of the ferromagnetic/nonferromagnetic interfaces under the two deposition rates. We also measured the temperature dependence of the magnetoresistance (MR), starting at 20 K, observing values between 9% and 16% for series 2 and between 13% and 16% for series 1. MR then decreased linearly with increasing for all SVs, vanishing at a temperature 0 of about 600 K, well below the bulk Curie point. However, we observed a striking difference between series 1 and series 2 in the temperature dependence of the GMR slopes, where GMR is the giant magnetoresistance.
Advanced Materials Research, 2014
The giant magnetoresistance (GMR) effect in FeMn/NiCoFe/Cu/NiCoFe spin valve prepared by dc opposed target magnetron sputtering is reported. The spin valve thin films are characterized by Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and magnetoresistance ratio measurements. All measurements are performed in room temperature. The inserted 45 mm thickness FeMn layer to the NiCoFe/Cu/NiCoFe system can increase the GMR ratio up to 32.5%. The coercive field to be increased is compared with different FeMn layer thickness. Furthermore, the coercive field (Hc) decreases with increasing FeMn layer thickness. Magnitude of coercive field is 0.1 T, 0.09 T and 0.08 T for FeMn layer thickness is 30 nm, 45 nm and 60 nm, respectively. The FeMn layer is used to lock the magnetization in the ferromagnetic layer through the exchange anisotropy. This paper will describe the development of a GMR spin valve and its magnetic properties.
Three-dimensional spin structure in exchange-biased antiferromagnetic/ferromagnetic thin films
Applied Physics Letters, 2009
A coexistence of lateral and in-depth domain walls in antiferromagnet/ferromagnet ͑AF/FM͒ thin films exhibiting double hysteresis loops ͑DHLs͒ is demonstrated. Comparison of single and DHLs together with local and global measurements confirms the formation of two oppositely oriented domains in the AF that imprint a lateral domain structure into the FM layer. Most significantly, the magnetization reversal mechanism within each opposite domain takes place by incoherent rotation of spring-like domain walls extending through the Ni thickness. Therefore, complex three-dimensional domain walls are created perpendicular and parallel to the AF/FM interface in exchange biased systems.
Temperature dependence of giant magnetoresistance properties of NiMn pinned spin valves
Journal of applied physics, 1998
The giant magnetoresistance response of NiMn pinned spin valves was studied at elevated temperature. Top spin valve films were made by ion beam sputtering and thermally treated to induce the strong unidirectional pinning field in the pinned layer. Both δR and δR/R decrease linearly with temperature. The sheet resistance of the spin valves also increases linearly with temperature. The exchange coupling between pinned layer and free layer decreases slightly and the coercivity of the free layer increases slightly. The temperature dependence of the exchange pinning field is unique in NiMn spin valves. The pinning field has a weakly increasing temperature dependence up to 200 °C, then decreases to zero at the blocking temperature of 380 °C. Samples with different thickness NiMn layers show different temperature dependencies. However, the blocking temperature is unchanged. The pinning fields of NiMn, FeMn, IrMn, and NiO spin valves were also measured up to 200 °C NiMn pinned spin valves show the least dependence of pinning field at elevated temperatures.