NiMn/FeNi exchange biasing systems–magnetic and structural characteristics after short annealing close to the phase transition point of the AFM layer (original) (raw)
Related papers
Journal of Magnetism and Magnetic Materials, 2003
We have investigated the magnetic and the structural characteristics of bi-layer exchange biasing (EB) systems NiMn-Co as function of the antiferromagnetic (AFM) film deposition parameters and of the post-deposition annealing and field-cooling procedures. The effects of sputtering pressure, growth rate, seed layer and of the annealing parameters were studied by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Magneto-Optical Kerr (MOKE) effect measurements. The results yielded optimised deposition conditions and permitted us to establish efficient annealing and field-cooling procedures. The best obtained EB systems with 5 nm Co film reveal coercive field H c X35 Oe and exchange bias field H EB X95 Oe and have good stability in air up to at least 2001C.
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 .
Physical Review Letters, 2008
For pOlycrystalline NiFe/FeMn bilayers, we have observed and quantified the rotation of the pinning direction in the exchange bias training and recovery effects. During consecutive hysteresis loops, the rotation of the pinning direction strongly depends on the magnetization reversal mechanism of the ferromagnet layer. The interfacial uncompensated magnetic moment of antiferromagnetic grains may be irreversibly switched and rotated when the magnetization reversal process of the ferromagnet layer is accompanied by domain wall motion and domain rotation, respectively.
Inhomogeneous magnetic field influence on magnetic properties of NiFe/IrMn thin film structures
Journal of Magnetism and Magnetic Materials, 2019
We demonstrate how the configuration and magnitude of a magnetic field, applied during magnetron sputtering of a NiFe/IrMn bilayer, influence the magnetic properties of the structure, such as hysteresis loop shape, coercivity, and exchange bias. Furthermore, we illustrate that it is possible to create a stepwise hysteresis loop in the sample's region with the highest field gradient. The found features can be used for future sensor applications.
Competing magnetic interactions in exchange-bias-modulated films
Physical Review B, 2010
The magnetization reversal in stripe-like exchange bias patterned Ni81Fe19/IrMn thin films was investigated by complementary inductive and high resolution magneto optical magnetometry, magneto optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange bias direction. Due to the interaction of interfacial coupling, exchange, and magneto-static energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micro-patterned exchange bias films.
Long range magnetic ordering with giant magnetic moments in Pt doped NiMn thin films
Journal of Applied Physics, 2009
Magnetization and electron spin resonance ͑ESR͒ measurements have been carried out on a 1.2 at. % Pt doped NiMn thin film ͑100 Å͒ in the temperature range of 5-150 K for both parallel ͑magnetic field parallel to the film surface͒ and perpendicular configurations. M versus H loops were recorded for each configuration at 5, 40, and 120 K. We have observed a number of differences between M versus H loops: for the perpendicular configuration, the hysteresis loops shift as a whole along the negative field axis ͑22 Oe at 5 K and 15 Oe at 120 K͒ for the field cooling case as a manifestation of the rigid component of the unidirectional anisotropy field, while no shift was observed for the parallel configuration. In addition, for the perpendicular configuration, M goes to the technical saturation value at a field much less than the corresponding demagnetization field ͑ϳ4M s ͒, indicating that this sample has a large bulk uniaxial anisotropy perpendicular to the film surface. It is also interesting that the observed saturation magnetization is much larger than the value ͑ϳ10.2 kOe͒ corresponding to the full alignments of Ni and Mn moments, exceeding the experimental uncertainty, leading us to suggest that orbital magnetism may be responsible for the enhanced saturation magnetization. Furthermore, the exchange stiffness constant ͑D͒, bulk anisotropy constant, and surface anisotropy constant were deduced from ESR data analysis. Based on magnetization and ESR results, we conclude that the magnetic behavior is compatible with the ESR fitting parameters. We also show that the competing asymmetric surface effects due to magnetostatic interactions play a crucial role in the overall magnetic behavior of this film.
Reversal of the Pinning Direction in the Synthetic Spin Valve with a NiFeCr Seed Layer
Nanomaterials
The effect of the seed layers on the magnetic properties of the giant magnetoresistance thin films has received a lot of attention. Here, a synthetic spin valve film stack with a wedge-shaped NiFeCr seed layer is deposited and annealed following a zero-field cooling procedure. The film crystallinity and magnetic properties are studied as a function of the NiFeCr seed layer thickness. It is found that the exchange coupling field from the IrMn/CoFe interface and the antiferromagnetic coupling field in the synthetic antiferromagnet both increase as the seed layer thickness increases, indicating the perfection of film texture. In this film, the critical thickness of the NiFeCr seed layer for the formation of the ordered IrMn3 texture is about 9.3 nm. Meanwhile, a reversal of the pinning direction in the film is observed at this critical thickness of NiFeCr. This phenomenon can be explained in a free energy model by the competition effect between the exchange coupling and the interlayer ...
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.
Surface pinning in ferromagnetic films with perpendicular anisotropy
Physical Review B, 2011
We have studied the ferromagnetic resonance response in a series of atomically disordered FePt thin films as a function of film thickness (9-200 nm) and excitation frequency (9.5 and 24 GHz). These films are characterized by a perpendicular anisotropy that promotes a stripelike magnetic domain structure above a critical thickness dcr~30 nm. All films display a resonant absorption due to the uniform precession of the magnetization vector. The analysis of the linewidth as a function of film thickness shows that the line broadens considerably above dcr. In the thinner films (d<28 nm) we have only observed the absorption related to the uniform precession mode, but thicker films, in which a stripe domain pattern is observed at zero field in static magnetic measurements, show an additional resonance line when the magnetic field is applied at, or very close to, the film plane normal. This line appears at fields below the main resonance and is observed at both X and K bands with approximately the same field separation from the uniform mode. We have also found that the line separation between the two resonances varies with the film thickness, indicating that the appearance of an additional resonance is related to confinement effects, but does not follow the quadratic law expected for infinite surface pinning. The ferromagnetic resonance results have been interpreted within a model of standing spin waves with finite surface pinning. From the angular variation of the pinning parameter close to the film normal we have found that the surface anisotropy is perpendicular to the film plane and increases with film thickness. The origin of the surface anisotropy seems to be related to a substrate-induced strain produced in the fabrication process and to a surface layer with a reduced magnetization. Annealing the samples at relatively low temperatures produces important changes in the resonance spectra. The overall observed behavior suggests that even though the resonance experiments are made at fields large enough to be in a magnetically saturated state, the formation of a stripe structure and the changes observed in the ferromagnetic resonance spectra above dcr are not completely uncorrelated phenomena.
Journal of Magnetism and Magnetic Materials, 2018
Exchange bias properties of NiFe/FeMn thin films have been investigated through X-ray diffraction, hysteresis loops, angular measurements of anisotropic magnetoresistance (AMR) and magnetic torque. As first predicted by Meiklejohn and Bean we found a decrease on the bias field as the NiFe layer thickness increases. However such reduction is not as strong as expected and it was attributed to the increase on the number of uncompensed antiferromagnetic spins resulting from the increase on the number of FeMn grains at the interface as the thickness of the NiFe layer is increased. The angular evolution of AMR and the magnetic torque were calculated and compared to the experimental ones using the minimization of the free magnetic energy and finding the magnetization equilibrium angle. The free energy, for each grain of the polycrystalline sample, is composed by the following terms: Zeeman, uniaxial, unidirectional and the rotatable energies. While from the AMR curves we obtain stable anisotropy fields independently on the measuring fields, from the torque curves we obtain increasing values of the uniaxial and rotatable fields, as the measuring field is increased. These results were attributed to the physical origin and sensitivity of the two different techniques. Magnetoresistance is mainly sensitive to the inner portion of the ferromagnetic layer, and the torque brings out information of the whole ferromagnetic layer including the interface of the layers. In this way, we believe that the increase in the uniaxial and rotatable values were due to an increase on the volume of the ferromagnetic layer, near the interfaces, which is made to rotate with the measuring field. Studying the rotational hysteresis by both techniques allows to separately obtain the contributions coming from the inner portion of ferromagnetic layer and from the interface.