Inter layer magnetic coupling in exchange bias and spin valve structures with Fe-Mn and Ir-Mn antiferromagnetic layers (original) (raw)
Related papers
Journal of Magnetism and Magnetic Materials, 2008
Exchange bias and spin valve systems with Fe-Mn antiferromagnetic layers of different Fe concentrations were obtained by the thermo-ionic vacuum arc method. The adherence of the multilayer system to the Si substrate depends on the Fe-Mn composition. The overall roughness depends on the growing order of the antiferromagnetic/ferromagnetic layers. Very low blocking temperatures for exchange bias were observed for the considered compositions of the Fe-Mn layer. The coercive forces of both the pinned and the free layers of spin valve structures can be considerably modified along a large set of samples simultaneously prepared. r
Physical Review B, 2010
We demonstrate an exchange bias in (Ga,Mn)As induced by antiferromagnetic coupling to a thin overlayer of Fe. Bias fields of up to 240 Oe are observed. Using element-specific x-ray magnetic circular dichroism measurements, we distinguish a strongly exchange coupled (Ga,Mn)As interface layer in addition to the biassed bulk of the (Ga,Mn)As film. The interface layer remains polarized at room temperature. PACS numbers: 75.70.Cn, 75.50.Pp, 75.50.Bb Ferromagnetic (FM) semiconductors offer the prospect of combining high-density storage and gate-controlled logic in a single material. The realization of spin-valve devices from FM semiconductors requires the controlled switching of magnetization in adjacent layers between antiferromagnetic (AFM) and FM configurations. This has motivated several theoretical investigations of interlayer coupling in all-semiconductor devices 1 , and AFM coupling has recently been demonstrated in (Ga,Mn)As multilayers separated by p-type non-magnetic spacers 2 . However, the Curie temperature T C of (Ga,Mn)As is currently limited to 185 K in single layers 3 , and is typically much lower for layers embedded within a heterostructure 2 , which is an obstacle to the practical implementation of semiconductor spintronics.
Structural and magnetic properties of (Fe/Mn) exchange-biased multilayers
Physica B: Condensed Matter, 2013
Exchange-biasing of ferromagnetic (F) Fe layers by adjacent antiferromagnetic (AF) Mn layers has been investigated in (Fe/Mn) 10 multilayered films. This study has been focused on the relationship between the evolution of the exchange-bias field and the evolution of the film microstructure as a function of the deposition temperature. The increase of the deposition temperature results in the formation of an Fe-Mn alloy at the interfaces and columnar features whose size increases with the deposition temperature. In parallel, the exchange-bias field decreases significantly, due to interface roughness. (C. Bordel). Physica B 416 (2013) 45-50
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.
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 .
Changes in ferromagnetic spin structure induced by exchange bias in Fe/MnF_ {2} films
2004
Depth-dependent Fe spin structures of the remanent state in exchange-coupled Fe/MnF 2 films have been probed using 57 Fe conversion electron Mössbauer spectroscopy, both above and well below the MnF 2 Néel temperature. 57 Fe probe layers were embedded either at the Fe/MnF 2 interface or in the center of the Fe film. Remarkably, exchange bias induces a significant change of the in-plane angular distribution of the Fe magnetic moments at the interface and inside the Fe film, away from the saturation magnetization direction. Results from vector magnetometry support these conclusions.
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.
Enhanced exchange bias in ferromagnet/antiferromagnet multilayers
Journal of Magnetism and Magnetic Materials, 2005
We study a series of NiFe ð10:0 nmÞ=½Ir 20 Mn 80 ð6:0 nmÞ=Co 80 Fe 20 ð3:0 nmÞ N multilayers with different numbers N of bilayers grown by DC magnetron sputtering. After field-cooling, SQUID and MOKE measurements show a sizable increase of the exchange bias field with N. X-ray specular and diffuse scattering data reveal no significant variation of the lateral correlation length and only a weak dependence of the vertical rms interface roughness on N. Atomic and magnetic force microscopy, however, show a strong reduction of the grain size accompanied by distinct changes of the magnetic domain structure. We conclude that the enhancement of the exchange bias effect is related to the shrinking of the domain size in the antiferromagnet due to the structural evolution in the multilayers. r
Physical Review B, 2008
The impact of in-plane alternating currents on the exchange bias, resistance, and magnetoresistance of a Co85Fe15/Ni0.85Co0.15O/Co85Fe15/Cu/Co85Fe15 spin-valve is studied. With increasing current, the resistance is increased while the maximum magnetoresistance ratio decreases. Noticeably, the reversal of the pinned layer is systematically suppressed in both field sweeping directions. Since Ni0.85Co0.15O oxide is a good insulator, it is expected that the ac current flows only in the Co85Fe15/Cu/Co85Fe15 top layers, thus ruling out any presence of spin-transfer torque acting on the spins in the antiferromagnetic layer. Instead, our measurements show clear evidences for the influence of Joule heating caused by the current. Moreover, results from temperature-dependent measurements very much resemble those of the current dependence, indicating that the effect of Joule heating plays a major role in the current-in-plane spin-valve configurations. The results also suggest that spin-transfer torques between ferromagnetic layers might still exist and compete with the exchange bias at sufficiently high currents.
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.