Heavy ion induced modifications on morphological, magnetic and magneto-transport behaviour of exchange biased Fe/NiO and NiO/Fe bilayers with Si substrate for spintronic applications (original) (raw)
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The role of defects on the magnetic behaviour of exchange coupled interfacial structures of Fe/NiO and NiO/Fe on Si substrates has been studied. For introduction of defects in the structures, swift (∼ 100 MeV) heavy ion irradiation has been used, which is known to cause structural and microstructural modifications. In our earlier study [Srivastava, N; Srivastava, P.C. J. Appl. Phys. 2012, 111, 123909] on similar structures, the significant magnetic behaviour (of exchange bias (EB) and coercivity) for Fe/NiO/nSi interfacial structure was observed and discussed in the realm of interfacial structural modification in the antiferromagnetic layer of the structure. The irradiated interfacial structures have been characterized from X-ray diffraction and M–H characteristics. Structural investigation has shown the formation of various silicide and oxide phases due to the irradiation-induced interfacial intermixing. A significant enhancement in EB field and coercivity has been observed for Fe/NiO/nSi interfacial structure on the irradiation (as compared to unirradiated ones). The observed enhanced EB and coercivity on the irradiation has been understood due to the creation of domain wall pinning centres across the interface as a result of ion irradiation. Moreover, the present study confirms the role of defects in the antiferromagnetic layer to cause the significant change in EB and coercivity. The observation supports the domain state model of EB in the exchange-coupled structures.
Effect of interface structure modifications on the properties of some magnetic multilayers
Journal of Alloys and Compounds, 2001
The effect of post-deposition thermal annealing on the interface structures of crystalline Fe-Tb multilayers and the associated changes in perpendicular magnetic anisotropy (PMA) has been studied using X-ray reflectivity, X-ray diffuse scattering and conversion electron Mossbauer spectroscopy. The main effect of annealing is a demixing at the interfaces attributed to a positive heat of mixing between Fe and Tb. Demixing is accompanied by a decrease in PMA due to increased shape anisotropy of the crystalline Fe layer. The results are compared with the effect of heavy ion irradiation in the same system.
Low temperature electronic and magneto-transport study across Fe/NiO bilayer on Si substrate has been reported. These bilayer structures have been irradiated by swift heavy ions (~ 100MeV Fe7+ ions with a fluence of 5×1012 ions/cm2). The electronic transport study across such bilayer (both unirradiated and irradiated) structures has shown the semiconducting nature of the interface. A significant decrease in current has been observed for the irradiated structure (as compared to unirradiated ones on the irradiation) which could be due to the irradiation induced introduction of defects/disorders in the structure. The magneto-transport study across unirradiated structure has shown the magnetic field sensitivity at low temperatures only whereas the irradiated structure has not shown any perceptible magnetic field sensitivity at low temperatures. Such observed intriguing feature of magnetic field sensitivity across the bilayer structures could be understood due to the motion of thermally assisted magnetic domain walls in the presence of external applied magnetic field. The observed high %MR could be related to spin-dependent electron scattering at the interfaces.
Swift iodine ion modification of the structural and magnetotransport properties of Fe/Cr systems
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
Fe/Cr/Fe trilayers and (Fe/Cr) 20 multilayers prepared under ultrahigh vacuum conditions by thermal evaporation were irradiated with 200 MeV I 13+ ions in the fluence range between 1 Â 10 11 and 8 Â 10 12 I/cm 2 . The structural properties of the Fe/Cr/Fe trilayers and (Fe/Cr) 20 multilayers were measured by X-ray reflectivity (XRR) and conversion electron Mössbauer spectroscopy (CEMS). Magnetic exchange coupling between the Fe layers through the Cr spacer layer was observed by SQUID magnetization measurements. Magnetoresistance effect was measured using four probe method at room temperature. The XRR spectra showed an increase of the interface roughness versus increasing irradiation fluence in the multilayers, while in the trilayers smoothening of the interfaces in the sample irradiated with fluence equal to 4 Â 10 11 I/cm 2 and very slight change for other fluences were observed. Improving of the interface structure in the trilayers at this fluence was observed also by CEMS. Moreover the Mössbauer spectra also confirm roughening of the interfaces as a function of fluence for multilayers. Before irradiation an antiferromagnetic coupling fraction dominated in all samples. After irradiation the changes of magnetic coupling were different in both types of samples. The trilayers were less sensitive to the irradiation fluence than multilayers and an increase of the antiferromagnetic fraction at small fluences was observed. In the multilayers a continuous decrease of the antiferromagnetic fraction as a function of fluence was evidenced. Vanishing of the antiferromagnetic coupling, observed for the largest fluence, resulted in the decrease of magnetoresistance effect in the Fe/Cr multilayers.
Interface States of Fe3O4/Si Interfacial Structure and Effect of Magnetic Field
Electronic transport across Fe3O4/Si interfacial structure has been studied with and without the application of magnetic fields along the interfacial plane, up to 8 kG. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics across the junction have been recorded for various bias voltages, frequency and magnetic field. The interfacial parameters, such as, ideality factor (n), barrier height (/B0), series resistance (RS) and donor concentration (ND) etc. have been estimated from the characteristics. The interface state density (NSS) and their energy distribution have been estimated by using the interfacial parameters. It has been observed that theNSSdecreases as the energy increases from the conduction band edge towards the valence band. A magnetoresistance (MR) of40% has been estimated from theI–V–Hdata along with its variation with magnetic field. The change of interface state density with the magnetic field shows a similar variation as MR versusH. From the observed variations, the interface states seem to be related to electronic spins. The possibility of an interfacial magnetic silicide or magnetic ions in the interfacial region has been invoked for the observed interface states.
Surfactant influence on interface roughness and magnetoresistance value in Fe/Cr multilayers
Thin Solid Films, 2013
Effect of interfacial roughness on magnetoresistance (MR) value in Fe/Cr multilayers was studied. The Fe/Cr multilayers were prepared on a MgO(100) substrate by molecular beam deposition technique and doped with Bi and In surfactants. The morphology of the layers, especially the interface structure, was studied using conversion electron Mössbauer spectroscopy (CEMS). CEMS spectra indicate an increase in the width of interfaces of modified samples; this effect is stronger for the sample doped with In. Auger electron spectroscopy shows the segregation of the surfactant to the surface. Magnetic and magnetotransport properties of the samples were studied by the magneto-optic Kerr effect and MR measurements. The observed hysteresis loops confirm in all samples antiferromagnetic arrangement of Fe layers sandwiched between Cr while the value of MR is larger for the doped samples. It was observed that roughening of the interfaces resulted in an increase of the MR effect.
Magnetic Interactions on Oxide Ferromagnet/Ferromagnetic Intermetallide Interface
Physics of the Solid State, 2019
The magnetic properties of heterostructures consisting of two films are studied. The upper layer involves rare-earth intermetallic nanostructured superlattices consisting of exchange-coupled layers (TbCo 2 /FeCo) n (TCFC), and the lower layer includes either epitaxial manganite La 0.7 Sr 0.3 MnO 3 (LSMO) with optimum strontium doping or an epitaxial film of an yttrium-iron garnet Y 3 Fe 5 O 12 (YIG) with a Bi additive. TCFC is a ferromagnet having high Curie temperature and provides controllable induced magnetic anisotropy. Experimental studies showed that the interlayer interaction of the TCFC/LSMO heterostructure is antiferromagnetic. There was an increase in the FMR line width in the structures due to the flow of a spin current through the interface between two films. There was electric voltage in the TCFC/YIG heterostructure induced in the TCFC intermetallide film, due to an inverse spin Hall effect under ferromagnetic resonance conditions.
Physical Review B, 2010
We demonstrate an exchange bias in (Ga,Mn)As induced by antiferromagnetic coupling to a thin overlayer of Fe. Bias fields of up to 240 Oe are observed. Using element-specific x-ray magnetic circular dichroism measurements, we distinguish a strongly exchange coupled (Ga,Mn)As interface layer in addition to the biassed bulk of the (Ga,Mn)As film. The interface layer remains polarized at room temperature. PACS numbers: 75.70.Cn, 75.50.Pp, 75.50.Bb Ferromagnetic (FM) semiconductors offer the prospect of combining high-density storage and gate-controlled logic in a single material. The realization of spin-valve devices from FM semiconductors requires the controlled switching of magnetization in adjacent layers between antiferromagnetic (AFM) and FM configurations. This has motivated several theoretical investigations of interlayer coupling in all-semiconductor devices 1 , and AFM coupling has recently been demonstrated in (Ga,Mn)As multilayers separated by p-type non-magnetic spacers 2 . However, the Curie temperature T C of (Ga,Mn)As is currently limited to 185 K in single layers 3 , and is typically much lower for layers embedded within a heterostructure 2 , which is an obstacle to the practical implementation of semiconductor spintronics.