Study of Exchange Bias in All Ferromagnetic Fe/Co Soft/Hard Bilayer (original) (raw)
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Magnetic Structure in Fe/Sm-Co Exchange Spring Bilayers with Intermixed Interfaces
2010
The depth profile of the intrinsic magnetic properties in an Fe/Sm-Co bilayer fabricated under nearly optimal spring-magnet conditions was determined by complementary studies of polarized neutron reflectometry and micromagnetic simulations. We found that at the Fe/Sm-Co interface the magnetic properties change gradually at the length scale of 8 nm. In this intermixed interfacial region, the saturation magnetization and magnetic anisotropy are lower and the exchange stiffness is higher than values estimated from the model based on a mixture of Fe and Sm-Co phases. Therefore, the intermixed interface yields superior exchange coupling between the Fe and Sm-Co layers, but at the cost of average magnetization.
New Journal of Physics, 2012
The magnetization reversal processes are discussed for exchangecoupled ferromagnetic hard/soft bilayers made from Co 0.66 Cr 0.22 Pt 0.12 (10 and 20 nm)/Ni (from 0 to 40 nm) films with out-of-plane and in-plane magnetic easy axes respectively, based on room temperature hysteresis loops and first-order reversal curve analysis. On increasing the Ni layer thicknesses, the easy axis of the bilayer reorients from out-of-plane to in-plane. An exchange bias effect, 2 consisting of a shift of the in-plane minor hysteresis loops along the field axis, was observed at room temperature after in-plane saturation. This effect was associated with specific ferromagnetic domain configurations experimentally determined by polarized neutron reflectivity. On the other hand, perpendicular exchange bias effect was revealed from the out-of-plane hysteresis loops and it was attributed to residual domains in the magnetically hard layer.
Journal of Physics D: Applied Physics, 2013
Sm-Co(20 nm)/Fe(t Fe) bilayers are fabricated with different Fe layer thicknesses (t Fe = 0, 2, 4, 6 and 8 nm) in order to systematically investigate the intermixing effect between Fe and Sm-Co layers and its influence on the magnetic properties. X-ray diffraction analysis indicates that the deposition of soft layer (Fe) promotes crystallization of hard layer (Sm-Co) at a low annealing temperature (400 • C). The annealed films consist of hexagonal Sm 2 Co 7 , Sm 2 Co 17 and SmCo 5 phases in the hard layer and bcc-structured Fe(Co) in the soft layer. Rutherford backscattering is employed to investigate the atomic composition of the individual layers and thereby the extent of diffusion of Co atoms into the Fe layer. The estimated Co content is higher for lower t Fe. The magnetic properties of the bilayers very close to the interface are analysed by the magneto-optical Kerr effect. The calculated Kerr intensities (which represent the magnetization process) are significantly affected by the extent of diffused Co in the Fe layer. Superconducting quantum interference device magnetic measurements demonstrate smooth and single-phase magnetic behaviour for t Fe up to 6 nm and a good combination of high coercivity (6.5 kOe) and high magnetic remanence (834 emu cm −3) is obtained for t Fe = 4 nm.
Journal of Applied Physics, 2015
ABSTRACT Magnetization reversal of antiferromagnetically coupled (AFC) soft and hard (Co/Pd) multilayers was studied as a function of temperature. While the hard [Co(0.3 nm)/Pd(0.8 nm)]�10 was kept unchanged, the softness of the [Co(t)/Pd(0.8 nm)]�3 was controlled by varying the thickness t of the Co sublayer. Clear two-step hysteresis loops were observed for all the investigated multilayers with t ranging between 0.4 and 1 nm. The spin reorientation of the soft layer magnetization from in-plane direction to out-of-plane direction was investigated from 50 to 300 K. The antiferromagnetic field HAFC measured from the shift of the minor hysteresis loop reveals a good agreement to the quantum-well model. From the out-of-plane hysteresis loop of the uncoupled soft layer, its magnetization shows an in-plane orientation for t�0.6 nm. The strong HAFC helps to induce an out-of plane orientation of the soft layer with a linear decrease of its coercivity with temperature. These investigated structures show the possibility to reduce the unwanted stray field and improving the out-of-plane anisotropy even for relatively thicker soft layer. VC
Physica B: Condensed Matter, 2015
Hysteresis loops of the nanoscale magnetic layer Co 90 Fe 10 and Ni 81 Fe 19 and bilayer Co 90 Fe 10 /Ni 81 Fe 19 and Ni 81 Fe 19 /Co 90 Fe 10 films were measured as a function of external dc magnetic field and the thickness dependence of these films were plotted as a function of temperature. Time evolution of the minor/ middle/major hysteresis loops of 5/5 nm-thick Ni 81 Fe 19 /Co 90 Fe 10 monolayer have been observed at 10 K. The spin valve, exchange bias training and Barkhausen effects for magnetic layer and bilayer films have been analysed at various temperatures, thicknesses and different orientations according to the substrate. The exchange-bias training effects have been observed only in positive magnetization region. Origin of the exchange-bias training effects and asymmetric hysteresis loops are related to the relaxation mechanism of a pinning layer in magnetically coupled soft/hard bilayers.
Applied Physics Express, 2012
Antiferromagnetic-ferromagnetic exchange coupling is known for its pinning effect on the magnetic hard layer through coercivity enhancement or exchange bias. This study reports its effect on controlling perpendicular magnetization in the soft magnetic regime. In a series of Ni 78 Fe 22 (Py)/Mn bilayers, we demonstrate that the magnetization, coercivity, and thermal stability of perpendicular anisotropy can be controlled by varying the thicknesses of the Py and Mn layers, based on the competition between the in-plane anisotropy of the Py layer and the out-of-plane-oriented Py-Mn exchange coupling. This offers a new possibility for the design of magnetic free layers in perpendicular-based magnetic logical devices.
Physical Review B, 2012
Magnetization reversal in nanoscale (Sm-Co)/Fe (hard/soft) bilayer exchange-spring magnets with in-plane uniaxial magnetic anisotropy was investigated by magnetometry, conversion-electron Mössbauer spectroscopy (CEMS) and atomistic Fe spin-structure calculations. Magnetization loops along the easy direction exhibit signatures typical of exchange-spring magnets. In-field CEMS at inclined γ -ray incidence onto thin (2 nm) 57 Fe probe layers embedded at various depths in the 20-nm-thick natural (soft) Fe layer provides depth-dependent information (via the line-intensity ratio R 23 as a function of the applied field H ) about the in-plane rotation of Fe spins. A minimum in the R 23 -vs-H dependence at (H min , R min ) determines the field where Fe magnetic moments roughly adopt an average perpendicular orientation during their reversal from positive to negative easy-axis orientation. A monotonic decrease of H min with distance from the hard/soft interface is observed. Rotation of Fe spins takes place even in the interface region in applied fields far below the field of irreversible switching, H irr , of the hard phase. Formation of an Fe-Co alloy is detected in the interface region. For comparison, the noncollinear Fe spin structure during reversal and the resulting R 23 ratio were obtained by electronic-structure calculations based on a quantum-mechanical Hamiltonian for itinerant electrons. The coupling at the hard/soft interface is described by the uniaxial exchange-anisotropy field, h int , as a parameter. Our calculated R 23 ratios as a function of the (reduced) applied field h exhibit similar features as observed in the experiment, in particular a minimum at (h min , R min ). R min is found to increase with h int , thus providing a measure of the interface coupling. Evidence is provided for the existence of fluctuations of the interface coupling. The calculations also show that the Fe spin spiral formed during reversal is highly inhomogeneous. In general, our simulation of the Fe spin structure is applicable for the interpretation of experimental results on layered exchange-spring magnets.
Low Temperature Physics, 2012
The influence of magnetic anisotropy of ferromagnetic film on the phenomenon of exchange bias is studied. Hysteresis behavior in the 2-spin model of a ferro/antiferromagnet (FM/AFM) bilayer with exchange bias has been investigated in detail. In this model a half-space of AFM with fixed magnetic configuration contacts with a 2-layer FM film. Twelve different types of magnetization curves M(H) (both with and without hysteresis) have been found. Some of the M(H) curves demonstrate unusual features, such as plateaus and inclined segments. The hysteresis loop becomes asymmetric if the surface anisotropy is taken into account. 0 2 2 0 J J J J H .
Origin and control of exchange-bias-like phenomenon in coupled ferromagnetic [Pt/Co]/NiFe bilayers
Physical Review B, 2011
Domain formation in a [Pt/Co] multilayer with out-of-plane anisotropy leads to a shift of the hysteresis loop of an adjacent NiFe thin film with in-plane anisotropy in an analogous manner to the exchange-bias phenomenon typically observed in ferromagnetic/antiferromagnetic systems. This paper shows that the loop shift can be gradually tuned through modification of the magnitude of the perpendicular anisotropy of the [Pt/Co]/NiFe system by simply varying the thickness of an underlying Pt buffer layer. Magnetometry, magnetotransport, and magnetic force microscopy experimental measurements were made. It appears that the key parameter which controls the exchange-bias effect in this system is the presence of a vortex core in between magnetic domains in the [Pt/Co] multilayer. The magnitude of the exchange-bias is related to the ability to unpin this vortex core, which is related to the magnitude of the perpendicular anisotropy. Micromagnetic simulations illustrate the magnetic configuration responsible for the exchange-bias phenomenon in this nonstandard exchange-biased type system.
Journal of Magnetism and Magnetic Materials, 2019
The M-H hysteresis curves of field cooled CoFe /FeMn bilayers and CoFe /FeMn /CoFe trilayers were studied to understand the exchange bias phenomena in these systems. The measured data revealed that the values of the exchange bias corresponding to a bottom CoFe layer reduced by about 23.5 % with an addition of another CoFe layer at the top of bilayer stack. It was also observed that, while this reduction in exchange bias of a bottom CoFe layer (calculated in %) depends on thicknesses of a top CoFe layer and an antiferromagnetic FeMn layer, it is independent of the thickness of bottom CoFe layer. As the strength of exchange bias depends on the presence of pinned uncompensated moments in an antiferromagnetic layer, our observations indicate that the FeMn layer consists comparatively lower amount of pinned uncompensated moments in trilayers. This reduction in pinned uncompensated moments of FeMn layer in trilayers is then co-related with the domain wall suppression in the FeMn layer in CoFe /FeMn /CoFe trilayers.