Magnetic and structural characteristics of exchange biasing systems based on NiMn antiferromagnetic films (original) (raw)
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Texture and magnetic properties of exchange bias systems
We report on the magnetic and structural properties of IrMn/CoFe exchange bias systems deposited onto a dual seed layer of NiCr͑X͒/Ru͑5 nm͒, with X = 2, 6, and 20 nm. Samples with the structure NiCr ͑Xnm͒/IrMn ͑7 nm͒/CoFe ͑3 nm͒/Ta ͑10 nm͒ with X = 2, 6, and 20 nm were prepared by dc sputtering for magnetic characterization. A second set of samples with structure NiCr ͑Xnm͒/IrMn ͑10 nm͒ with X = 2, 6, and 20 nm were deposited onto TEM grids for structural characterization by TEM. A method of manipulating of the TEM grid to allow a qualitative analysis of the in-plane texture of the samples is described and used to analyze the microstructure of these samples. The microstructure and particularly the texture are correlated with the anisotropy constant ͑K AF ͒ of the antiferromagnet ͑AF͒ layer, with an optimum NiCr seed layer of 6 nm to give a maximum value of K AF of 1.2ϫ 10 7 ergs/ cc.
Effect of Granular Spacer on the Exchange Bias Effect in FeMn-Based Film Structures
Physics of Metals and Metallography, 2018
The article deals with a study of interactions between permalloy layers separated by granular Со-Al 2 O 3 spacer. Multilayer Ta/FeNi/FeMn/FeNi/Co-Al 2 O 3 /FeNi/Ta films prepared by magnetron sputtering are the test object. The spacer thickness and content of metallic phase in the spacer have been varied from 0 to 8 nm and 0 to 40%, respectively. A correlation has been found between the Co concentration in the spacer and critical spacer thickness. When the thickness of the spacer exceeds a critical value, the independent magnetization reversal of the permalloy layers adjacent the spacer takes place. It has been shown that, in the case of both cooperative and independent magnetization reversal of permalloy layers, the presence of a spacer substantially affects the hysteretic properties of film structure. The data obtained can be useful when purposefully controlling the coercive force and exchange-bias field in film structures with the unidirectional anisotropy.
Annealing effects on the structure and magnetic properties of Ni/Ti multilayers
Journal of Magnetism and Magnetic Materials, 1993
Fe-C granular films with different Fe volume fraction x v were fabricated using a DC facing-target sputtering system at room temperature and subsequently annealed at different temperatures. X-ray diffraction and selected area electron diffraction analyses indicate that as-deposited and low-temperature annealed ( 350 • C) samples are composed of amorphous Fe and C, and higher temperature annealing makes the amorphous Fe transform to α-Fe, which is also confirmed by high-resolution transmission electron microscopy. Magnetic measurements indicate that at room temperature the as-deposited Fe-C (x v = 58) granular films are superparamagnetic and annealed ones are ferromagnetic. The coercivity of 100 nm thick Fe-C (x v = 58) granular films increases with annealing temperature (for 1 h) and time (at 450 • C). The coercivity of the 100 nm thick Fe-C (x v = 58) samples annealed at temperatures ranging from 400 to 500 • C decreases linearly with measuring temperature T , signalling a domain wall motion mechanism. For the samples annealed at 550 • C, the change of in-plane coercivity with T satisfies the relation H c ∼ T 1/2 , reflecting that this system behaves better as a set of Stoner-Wohlfarth particles. It was also found that there exists a critical thickness (∼133 nm) for the 450 • C annealed (for 1 h) Fe-C (x v = 58) granular films with thickness in the range 100-200 nm, below and above which the magnetization reversal is dominated by domain wall motion and by Stoner-Wohlfarth rotation, respectively.
Antiferromagnetic layer thickness dependence of the IrMn/Co exchange-bias system
Physical Review B, 2003
We have investigated the dependence of magnetic anisotropies of the exchange-biased NiFe/FeMn/CoFe trilayers on the antiferromagnetic ͑AF͒ layer thickness ͑t AF ͒ by measuring in-plane angular-dependent ferromagnetic resonance fields. The resonance fields of NiFe and CoFe sublayers are shifted to lower and higher values compared to those of single unbiased ferromagnetic ͑F͒ layers, respectively, due to the interfacial exchange coupling when t AF Ն 2 nm. In-plane angular dependence of resonance field reveals that uniaxial and unidirectional anisotropies coexist in the film plane, however, they are not collinear with each other. It is found that these peculiar noncollinear anisotropies significantly depend on t AF . The angle of misalignment displays a maximum around t AF = 5 nm and converges to zero when t AF is thicker than 10 nm. Contributions from thickness-dependent AF anisotropy and spin frustrations at both F/AF interfaces due to the structural imperfections should be accounted in order to understand the AF-layer thickness dependence of noncollinear magnetic anisotropies.
Physical Review B, 2007
We have studied the magnetic properties of ͓Ag͑t Ag ͒ /Co͑1.2 nm͔͒ 60 multilayers grown in an oxygen atmosphere. Partial oxidation of the Co layers results in the appearance of t Ag dependent exchange-bias properties. A strong increase in the exchange-bias field H E together with a significant reduction in the coercivity H C are observed when t Ag is decreased below t Ag * = 4 nm, whereas these two parameters adopt approximately constant values for t Ag Ͼ t Ag * . At t Ag * , a transition from continuous to islandlike silver layers ͑on reducing t Ag ͒ is signaled by electrical resistivity and x-ray reflectivity results. From magnetic hysteresis loops recorded at room temperature and magnetization curves, it is concluded that this transition induces a granular morphology in the Co regions, which are previously ͑t Ag Ͼ t Ag * ͒ plateletlike, and enhances the oxidized fraction of Co ͑f CoO ͒. The increase ͑decrease͒ in H E ͑H C ͒ with reducing t Ag below t Ag * is correlated to the increase in both the electrical resistivity and f CoO . From the latter correlation, we infer that the higher degree of oxidation in the granular Co layers is associated with effectively thicker antiferromagnetic ͑CoO͒ regions than in the t Ag Ͼ t Ag * ͑continuous multilayer͒ case-with correspondingly higher magnetic anisotropy energies-which may account for both the enhancement in H E and the reduction in H C . In addition, our study provides information on the surfactant effect of O 2 in Ag sputter growth since the continuity thickness value ͑t Ag * =4 nm͒ is found to be lower than those previously reported in nonreactive sputtering of Ag.
Journal of Magnetism and Magnetic Materials, 2014
Magnetic films and multilayers are the focus of much attention motivated mainly by their wide range of applications, such as magnetic data storage devices and sensors. The magnetic multilayer structures are normally prepared through physical means of deposition, as molecular beam epitaxy (MBE) or sputtering. However, there are already examples of materials produced by electrochemical routes, which share with the other deposition techniques a high sensitivity of magnetic and transport properties of the samples on their crystallographic and chemical structure. In addition, electrochemical deposition allows growing structures with high aspect ratio, which are not possible to obtain by MBE deposition followed by lithographic processes. The present work investigates the Co/Ni bilayered nanocrystalline films produced through the temperature-elevated electrochemical deposition, and modified by annealing carried out also under an external magnetic field. The results indicate an increase of the coercive field of deposited Co/Ni bilayers, when the electrodeposition process was conducted under magnetic field of 1 T. The annealing processing caused further remarkable increase of the coercive field of as-prepared bilayers that has been preserved under magnetic annealing conditions. The magnetic properties are discussed in terms of samples microstructure. In as-prepared samples the in-plane magnetization was observed, while high temperature treatment, causing microstructural changes in the film, resulted also in appearance of a small component of magnetization oriented perpendicularly to the films' plane that could have been observed by MFM analysis. The induced perpendicular magnetization component in the post-annealed samples was a result of the magnetic field applied in the perpendicular direction to the samples' surface during annealing treatment.