Changes in ferromagnetic spin structure induced by exchange bias in Fe/MnF2films
Ivan Schuller2004, Physical Review B
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Direct measurement of depth-dependent Fe spin structure during magnetization reversal in Fe/MnF2 exchange-coupled bilayers
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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.
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The angular dependence of the magnetic anisotropy of exchange biased Fe/MnF 2 bilayers was measured. Below the Néel temperature of the antiferromagnetic MnF 2 layer, an exchange anisotropy is observed which consists of unidirectional, uniaxial, threefold and fourfold symmetry components. The threefold exchange anisotropy term is responsible for the asymmetric magnetization reversal process recently observed in this system.
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Two different Fe/MnF 2 samples have been prepared by e-beam evaporation on MgO(001) substrates. The Fe layer in the samples includes a 10 Å thick 57 Fe probe layer either at the Fe/MnF 2 interface (interface sample) or 35 Å away from the interface (center sample). The samples are characterized by X-ray diffraction, B. Sahoo (B) · W. Keune · V. Kuncser
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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
INTERFACIAL SPIN CONFIGURATION IN EXCHANGE COUPLED MAGNETIC PHASES: EXCHANGE-SPRING AND EXCHANGE-BIAS SYSTEMS∗
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.
Angular dependence of the magnetization reversal in exchange-biased Fe∕MnF[sub 2]
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A detailed study of exchange-biased Fe/MnF 2 bilayers using magneto-optical Kerr Effect shows that the magnetization reversal occurs almost fully through domain wall nucleation and propagation for external fields parallel to the exchange bias direction.
Magnetization depth dependence in exchange biased thin films
Applied Physics Letters, 2006
The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet (AF/FM) exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF2/FM (FM=Fe, Ni, and Py) bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature (T_N) is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T_N have also been discussed. The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet ͑AF/ FM͒ exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF 2 /FM ͑FM= Fe, Ni, and Py͒ bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature ͑T N ͒ is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T N have also been discussed.
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The spin reorientation transitions in the intermetalfic compounds NdFe12_xVx (x ffi 2.2, 2, 1.8), which crystallize in the tetragonal ThMn12 structure, have been studied by M~Sssbauer and magnetization measurements on oriented absorbers. The spin reorientation has its onset in the range of 110-130 K and is completed in a few kelvin. The MiSssbauer spectra have been analyzed with a model which takes into account the preferential occupation by V of the i-sites in the ThMn12 structure. The temperature dependence of the canting angle has been determined both by this analysis and from the magnetization data, 0304-8853/90/$03.50 © 1990 -Elsevier Science Publishers B.V. (North-Holland)
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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.
Magnetization depth dependence in exchange biased thin films
Applied Physics Letters, 2006
The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet (AF/FM) exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF2/FM (FM=Fe, Ni, and Py) bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature (T_N) is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T_N have also been discussed. The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet ͑AF/ FM͒ exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF 2 /FM ͑FM= Fe, Ni, and Py͒ bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature ͑T N ͒ is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T N have also been discussed.
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