Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: Layer-resolved ^{57}Fe Mössbauer spectroscopy and electronic structure calculations (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.
We investigate equilibrium properties of an exchange-spring magnetic system constituted of a soft layer (e.g., Fe) of a given thickness on top of a hard magnetic layer (e.g., FePt). The magnetization profile M(z) as a function of the atomic position ranging from the bottom of the hard layer to the top of the soft layer is obtained in two cases with regard to the hard layer: (i) in the case of a rigid interface (the FePt layer is a single layer), the profile is obtained analytically as the exact solution of a sine-Gordon equation with Cauchy’s boundary conditions. Additional numerical simulations also confirm this result. Asymptotic expressions of M(z) show a linear behavior near the bottom and the top of the soft layer. In addition, a critical value of the number of atomic planes in the soft layer, that is necessary for the onset of spin deviations, is obtained in terms of the anisotropy and exchange coupling between the adjacent plane in the soft layer. (ii) In the case of a relaxed interface (the FePt layer is a multilayer), the magnetization profile is obtained numerically for various Fe and FePt films thicknesses and applied field.
Study of Exchange Bias in All Ferromagnetic Fe/Co Soft/Hard Bilayer
IEEE Transactions on Magnetics, 2014
We report the unusual and exotic phenomenon of positive exchange bias observed in all ferromagnetic layered soft/hard Fe/Co spring magnet systems. Interestingly, the results are well reproducible both at low (5 K) and room temperatures (300 K). The effect of applied magnetic pinning field of 7 and −5 T reveals a noticeable shift of magnetic hysteresis loops along the field direction. We argue that the reason behind observed positive exchange bias is the establishment of antiferromagnetic (AFM) exchange coupling at the interface as a result of intermixing of Fe into the Co layer. The collective coupling of this intermix layers is AFM which facilitates positive shift of magnetic hysteresis loop.
The influence of the interfacial spin configuration on specific magnetic phenomena in exchange coupled magnetic phases is briefly discussed. The ability of the 57 F e Mössbauer technique to reveal the spin structures at the interface of iron containing magnetic phases is emphasized for some particular cases. Experimental results obtained on layered exchange-bias systems and on nanocomposites exchange-spring magnets are presented. The influence of the ferromagnetic top layer on the interfacial spin configuration of the bottom antiferromagnetic layer of the F e/F eSn2 exchange-bias system is illustrated. A possibility for evaluating the inter-phase coupling strength via Mössbauer spectroscopy in F e/Nd2F e14B exchange-spring ribbons is described. * The financial support by the Deutsche Forschunggemeinschaft (SFB 491) and Romanian CEEX Project 35/2005 is highly appreciated.
Spin structure of exchange-biased NiFe∕FeMn∕NiFe trilayers
Journal of Applied Physics, 2007
The magnetic hysteresis curves of NiFe͑t͒ / FeMn͑15 nm͒ / NiFe͑5 nm͒ exchange-biased trilayers, with t ranging from 3.8 to 18 nm, show two clearly separated loops, which were interpreted as corresponding to the independent magnetic reversal of the two ferromagnetic ͑FM͒ NiFe layers. Polarized neutron reflectometry allowed the determination of the evolution of these two layer magnetizations at various fields along the hysteresis curve. For increasing t, the behavior of the magnetization evolved from one where both layer magnetizations were always collinear to the applied field to one where rotation of the magnetizations was observed at various fields. Measurements on the thickest field-annealed sample additionally showed that, during the reversal, the magnetizations of the two NiFe layers are close to being perpendicular to each other. This magnetic configuration is discussed in terms of the FM/antiferromagnetic ͑AFM͒ interactions and of a possible coupling between the two FM layers across the thick AFM FeMn spacer.
2011
Magnetization reorientation from in-plane to perpendicular direction, observed in Co thin film coupled antiferromagnetically to high perpendicular magnetic anisotropy (Co/Pd) multilayers, is studied systematically for Co thickness ranging from 0 to 2.4 nm. The sample with 0.75 nm thick Co showed an exchange coupling field (H ex ) exceeding 15 kOe at room temperature and 17.2 kOe at 5 K. With an increase of Co thickness, H ex decreased as expected and beyond certain thickness, magnetization reorientation was not observed. Indeed, three regions were observed in the thickness dependence of magnetization of the thin layer; one in which the thin layer (in the thickness range up to 0.8 nm) had a perpendicular magnetic anisotropy due to interface effects and antiferromagnetic coupling, another in which the thin layer (0.9-1.2 nm) magnetization had no interface or crystallographic anisotropy but was reoriented in the perpendicular direction due to antiferromagnetic coupling, and the third (above 1.2 nm) in which the magnetization was in-plane. In addition, Hall effect measurements were carried out to observe the anomalous and planar Hall voltages and to quantify the perpendicular and in-plane components of magnetization. The sample with thicker Co layer (2.4 nm) showed an in-plane component of magnetization, whereas the sample with 0.75 nm Co showed no in-plane component. The high value of H ex observed in 0.75 nm Co samples can have important implications in spintronics and bit patterned media.
Reversal modes of the multilayer exchange-spring magnet
Journal of Magnetism and Magnetic Materials, 2001
A one-dimensional micromagnetic model of the multilayer exchange-spring magnet is utilized for calculating the analytical expression of the di!erential susceptibility at the nucleation "eld in terms of structural parameters. The phase diagram in the plane of half-layer thicknesses is given for a Sm}Co/Fe multilayer, showing the critical line of PR, which is the boundary for the irreversible demagnetization mode. For thin layers the optimum soft-phase volume fraction is deduced.
Physical Review B, 2008
We measured directly the depth-dependent Fe spin rotation upon magnetization reversal in exchangecoupled Fe/ MnF 2 bilayers using nuclear resonant scattering of synchrotron radiation from an 57 Fe-probe layer buried at different depths within the Fe film. Our results show that the exchange-biased ferromagnetic layer develops a noncollinear spin structure along the film normal direction, reminiscent of a partial domain wall parallel to the Fe/ MnF 2 interface. This is contrary to most theoretical models of exchange bias which assume a collinear spin structure in the ferromagnetic layer.
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.
Asymmetry in the static and dynamic magnetic properties of a weak exchange spring trilayer
Journal of Magnetism and Magnetic Materials, 2005
Experimental results and theoretical calculations are presented for the static and dynamic magnetic properties of a weak exchange-spring symmetric FeTaN/FeSm/FeTaN trilayer. Static properties were investigated by means of alternating gradient field and magneto-optic Kerr effect magnetometries. The frequencies of three spin wave modes were measured by inelastic light scattering from long wavelength thermal spin waves. The combined analysis of spin wave frequencies and magnetometry data provides a consistent set of exchange, anisotropy and film thickness parameters.