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ABSTRACT: Compositional and temperature dependent ferromagnetic/anti-ferromagnetic transition of highly textured Fe<sub>100 - x</sub>Rh<sub>x</sub> (where x = 35 to 65) thin films deposited epitaxially on MgO (001) single crystal substrates were studied. First-order transition from ferromagnetic to anti-ferromagnetic phase was observed around 48 at. % Rh where x-ray diffraction spectra revealed a sharp discontinued decrease in lattice parameter- c coupled with a sudden decrease in magnetization from 1600 to 200 emu/cm<sup>3</sup>. The transition was sharp compared to non-textured randomly oriented thin films, bearing similarities to bulk FeRh. Temperature-dependent x-ray diffraction spectra and magnetic measurements revealed the occurrence of temperature induced anti-ferromagnetic to ferromagnetic phase transitions for films with Rh content larger than 47 at. %. The temperatures at which such transitions occurred were dependent on the Rh content, and broadened with increasing amounts of Rh.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
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ABSTRACT: The effect of the CrRu–SiO x underlayer with different doping concentrations and the thickness of the CrRu underlayer on the microstructure and magnetic properties of FePt–C films were investigated. FePt films exhibited L1 0 (001) texture at various SiO x doping concentrations. The coercivities were as large as 28 kOe and the slope of M–H loop at coercivity was approximately equal to 1, suggesting that FePt grains were well exchange decoupled. Grain size was only slightly reduced after introducing the CrRu–SiO x underlayer. But the contact angle between the FePt grains and the MgO intermediate layer around 135° indicated the a MgO intermediate layer was not favored for smaller grains to obtain good L1 0 (001) texture. X-ray photoelectron spectroscopy in-depth profile showed that Si diffused into a whole FePt–C layer and C diffused to the film surface.
Journal of Applied Physics 05/2011; · 2.17 Impact Factor
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ABSTRACT: In this study, L1 1 CoPt (111) films were deposited on glass substrates at 300 °C with observed superlattice (111) and (333) peaks and easy axis distribution of 2°. The magnetic anisotropy constant was in the order of 10<sup>7</sup> erg/cm<sup>3</sup>. The effect of CoPt layer thickness on domain structure and magnetic properties was investigated. With increasing film thickness, the squareness was reduced and the nucleation field changed from negative to positive, indicating low impedance to domain wall motion and increased demagnetizing energy. Magnetic force microscopy images demonstrated the magnetic domain structure changed from irregular and large domains to highly interconnected stripes with increasing CoPt layer thickness.
Journal of Applied Physics 05/2011; · 2.17 Impact Factor
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ABSTRACT: We report the effect of Mn doping on temperature-dependent magnetic properties of L10 FeMnPt (001) epitaxial films. (001) textured L10 Fe50−xMnxPt50 (x = 0, 5, 10, 15, 20 at. %) films were prepared by cosputtering Fe, Pt, and Mn onto MgO single crystal substrates at 550 °C. θ–2θ XRD scans indicated the lattice parameter c increased whereas the ordering parameter S decreased with Mn doping. The thermal magnetic properties measured using a superconducting quantum interference device showed that Curie temperature TC could be reduced to 500 K with 15 at. % Mn doping, but Ku was decreased to 1.6 × 107 erg/cm3. The relation of temperature-dependent anisotropy and saturation magnetization showed that it did not obey the Callen–Callen theory.
Journal of Applied Physics 04/2011; 109(7):07B747-07B747-3. · 2.17 Impact Factor
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ABSTRACT: Multilayer exchange spring media were fabricated by subsequently reducing the deposition temperature of the FePt-C film from the bottom layer to the top layer. Magnetic anisotropy and coercivity of FePt-C film increased with the increasing of deposition temperature because the chemical ordering of L10 FePt improved with deposition temperature. A two-layer microstructure was observed in the multilayer samples with a closely-packed granular hard layer and an isolated granular overlayer consisting of the soft magnetic layers deposited at lower temperatures. The coercivity of the tri-layer media was reduced to 5.4 kOe, half of that of the hard single layer FePt-C (10.8 kOe). The thermal stability of the multilayer structure was maintained although some soft magnetic layers involved.
Journal of Applied Physics 03/2011; 109(6):063910-063910-8. · 2.17 Impact Factor
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ABSTRACT: In this work, effects of exchange coupling of soft magnetic layer on switching field and magnetization reversal behaviour of CoPt-SiO2(soft)/CoPt-SiO2(hard) exchange coupled media were investigated. With increasing the thickness of the soft layer, both the coercivity and magnetization squareness of composite media decreased. Soft layer thickness 4 nm and below was more effective to significantly reduce the switching field than that above 4 nm. More incoherent switching behavior was observed with increasing soft layer thickness.
Journal of Nanoscience and Nanotechnology 03/2011; 11(3):2607-10. · 1.56 Impact Factor
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ABSTRACT: This paper presented the usage of the NiW/Ru underlayer to replace the single Ru underlayer for promoting CoPt hcp (0002) texture. Fcc (111) textured NiW film was used to induce the Ru hcp (0002) texture. It was found that the utilization of the (111) textured NiW alloying layer promoted the formation of Ru(0002) texture, enhanced the magnetic grain isolation and generated the uniform grains with gain size less than 10 nm in CoPt-SiO2 recording layer. The out-of-plane coercivity was also enhanced with the growth of 10 nm NiW underlayer below the Ru layer.
Journal of Nanoscience and Nanotechnology 03/2011; 11(3):2636-9. · 1.56 Impact Factor
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ABSTRACT: In this work, we prepared SmCo5 thin films with (0001) texture exhibiting perpendicular anisotropy in a wide range of Sm(x)Co(100-x) compositions (x = 13.2 approximately 37.0) on Cu/Ta underlayers. At a composition of Sm16.7Co83.3 (SmCo5), the SmCo5 film exhibits a maximum perpendicular coercivity of 18.2 kOe, which is attributed to a good crystallinity and an excellent (000l) texture. The SmCo5 (000l) peaks are shifted to smaller angles compared to the standard powder sample which indicates the formation of a SmCoCu alloy through Cu diffusion. The EDX result for this sample gives a composition of SmCo3Cu2.1 which confirms Cu diffusion into the SmCo5 layer. TEM image shows that SmCo5 film is well crystallized with a grain size of 50 nm.
Journal of Nanoscience and Nanotechnology 03/2011; 11(3):2644-7. · 1.56 Impact Factor
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ABSTRACT: In this report, the effect of simultaneously adding two dopants (C and Ta2O5) in FePt was investigated. (Fe55Pt45)79C21-(x vol%) Ta2O5 films (where x = 0% to 20%) were prepared using both low and high power magnetron sputtering on MgO (2 nm)/CrRu (30 nm) underlayers with in-situ heating at 350 degrees C. Films deposited at low power showed a decrease in exchange coupling with increasing Ta2O5 content. Out-of-plane coercivity of 7.2 kOe was observed even with up to 20 vol% Ta2O5. X-Ray diffraction spectra showed presence of FePt(001) texture for all compositions of Ta2O5 ranging from 0 to 20 vol% suggesting that the perpendicular anisotropy was maintained even with up to 20 vol% of dopant content. Films deposited at high power showed a different behavior with an initial increase in out-of-plane coercivity to 8.2 kOe and a reduction in exchange coupling with loop slope parameter (alpha) approaching a fully decoupled value of 1. Further increase in doping content led to deterioration in the out-of-plane coercivity, as well as an increase in the exchange coupling.
Journal of Nanoscience and Nanotechnology 03/2011; 11(3):2588-92. · 1.56 Impact Factor
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ABSTRACT: We reported the fabrication of (001) textured FePt – TiO <sub>2</sub> exchange coupled composite (ECC) media including hard/soft bilayer and multilayer with well isolated columnar microstructures. The magnetic anisotropy of FePt – TiO <sub>2</sub> was adjusted by applying various substrate bias during film deposition. The cross-sectional transmission electron microscopy images showed isolated granular microstructures in single hard layer, bilayer, and multilayer media. For the bilayer media, it was observed that both the coercivity and magnetization squareness of composite media decreased with increasing thickness of the soft layer. A soft layer with the thickness of 4 nm was more effective to significantly reduce the switching field and maintain a higher thermal stability factor than that of others. Incoherent switching behavior was observed as the soft layer thickness was increased to 6 nm. For multilayer media, it was found that the out-of-plane coercivity decreased to 6.5 kOe, which was close to half of that of the single hard layer. However, the thermal stability factor of the multilayer media slightly decreased compared with the single hard layer and bilayer media due to finite thickness. The results suggested a way to obtain the adjustable anisotropy for ECC media in high density magnetic recording application.
Journal of Applied Physics 07/2010; · 2.17 Impact Factor
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ABSTRACT: The effects of L1<sub>0</sub> CoPt-TiO<sub>2</sub>/FePt-TiO<sub>2</sub> bilayer and (Co<sub>x</sub>Fe<sub>100-x</sub>)<sub>50</sub>Pt<sub>50</sub>-TiO<sub>2</sub> (0 ¿ x ¿ 100 at.%) multilayer exchange coupled media on switching field and magnetization reversal mechanism were studied. Results showed that both bilayer and multilayer exchange coupled media with out-of-plane anisotropy in the hard and soft layers were effective to reduce the switching field of single layer FePt-TiO<sub>2</sub> media. First order reversal curve (FORC) distribution indicated that switching field distribution in the bilayer and multilayer exchanged coupled media was significantly narrowed down compared to the single layer and magnetization reversal was ascribed to domain formation followed by domain wall motion.
IEEE Transactions on Magnetics 07/2010; · 1.36 Impact Factor
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ABSTRACT: In this work, we have successfully induced SmCo<sub>5</sub>-(0001) texture using the Ni<sub>4</sub>W-(211) underlayer. A tungsten (W) seed layer of 4 nm resulted in a nanocrystalline (211)-textured Ni<sub>4</sub>W underlayer deposited at room temperature. Highly (0001)-textured SmCo<sub>5</sub> was achieved after the sputtering deposition in the temperature range of 500-540°C. The crystallinity of the SmCo<sub>5</sub> layer was reduced at higher deposition temperature (¿ 550°C), probably due to W diffusion. The nano-grained SmCo<sub>5</sub> thin film deposited at 500°C shows an out-of-plane coercivty of 12.7 kOe with a large perpendicular magnetic anisotropy. The thickness of Ni<sub>4</sub> W underlayer can be reduced to 13 nm without a significant change in the large perpendicular magnetic coercivity of the SmCo<sub>5</sub> thin film.
IEEE Transactions on Magnetics 07/2010; · 1.36 Impact Factor
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ABSTRACT: Tri-layer FePt–C graded media composed of three FePt–C layers with each single FePt–C layer deposited at different substrate temperatures were fabricated. The single hard layer FePt–C had a large coercivity of 11.4 kOe, while the coercivity of the tri-layer sample was only 5.7 kOe. A coercivity reduction factor of 2 was achieved without sacrificing the thermal stability of the media. The tri-layer media revealed incoherent magnetization switching—domain wall propagation. The microstructure showed that the tri-layer FePt–C graded media were graded media combined with modified coupled granular continuous (CGC) media. This new kind of graded media had a lower switching field and comparable thermal stability and should have the advantage of CGC media—lower transition noise.
Journal of Physics D Applied Physics 04/2010; 43(18):185001. · 2.54 Impact Factor
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ABSTRACT: Crystallographic structure, growth induced miscibility gap and strain in Ta/Co100−xPtx (0 ≤ x ≤ 43 at%)/Ru/Ta/glass films deposited at ambient temperature were investigated using polarized x-ray absorption spectroscopy to clarify the origin of observed perpendicular magnetic anisotropy (PMA) in Co72Pt28 film. Extended x-ray absorption fine structure spectroscopy data at Co K-edge showed that Co has a similar local atomic environment and averaged interatomic distance in the in-plane and out-of-plane polarization geometries for Co72Pt28, ruling out the contribution of magneto-elastic anisotropy and growth induced structural anisotropy as the origin of PMA. A large PMA in Co72Pt28 film was attributed to the preferred hexagonal close-packed stacking as observed using the x-ray absorption near-edge structure spectroscopy.
Journal of Physics D Applied Physics 09/2009; 42(18):185007. · 2.54 Impact Factor
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ABSTRACT: Exchange coupled L10 CoPt–Ta2O5 multilayer media of gradually reducing coercivity from bottom to top layer were demonstrated to reduce the coercivity of hardest layer. The coercivity of different layers was tuned by adjusting the Ta2O5 content. The coercivity of 12 nm hardest layer was reduced by factor of three using multilayer media of total thickness 20 nm. The exchange coupled media comprising 12 nm hardest layer and 8 nm softest layer was able to reduce the coercivity only by factor of two. This indicates that multilayer media is more effective to reduce the switching field than the exchange coupled media.
Applied Physics Letters 06/2009; 94(23):232502-232502-3. · 3.84 Impact Factor
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ABSTRACT: In this work, we have studied the influence of seed layer on the microstructure of the Cu underlayer and its effect on the structure and magnetic properties of subsequently deposited SmCo <sub>5</sub> films. Our investigation concentrated on the thickness effect of Ta seed layer. Our study has shown that a smooth Ta seed layer can lead in a highly textured and well crystallized (111) Cu underlayer. At 4 nm (Ta thickness), the full width at half maximum of the rocking curve (Δθ<sub>50</sub>) of Cu (111) diffraction peak is only 3.3° and the surface root-mean-square roughness (Rq) of Cu surface is only 0.53 nm. With the smooth and highly (111) textured Cu underlayer, the superstructure SmCo <sub>5</sub> (000l) peaks are clearly observed. Also, the good texture of SmCo <sub>5</sub> results in a high perpendicular coercivity around 20 kOe with a large perpendicular anisotropy.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: L1<sub>0</sub> FePt – Ta <sub>2</sub> O <sub>5</sub> films with (001) texture were synthesized by cosputtering FePt and Ta <sub>2</sub> O <sub>5</sub> targets and in situ heated at 350 ° C . The (001) preferred orientation was preserved even when doped with 20 vol % Ta <sub>2</sub> O <sub>5</sub> . The out-of-plane coercivity, H<sub>c</sub> , increased from 6.7 kOe (for pure FePt film) to 8.8 kOe when doped with 20 vol % Ta <sub>2</sub> O <sub>5</sub> . Further increase in the dopant content to 25 and 30 vol % caused H<sub>c</sub> to decrease significantly to below 3 kOe. Well-isolated FePt grains of tall column structures were observed for the 12 nm thick FePt film when doped with 20 vol % . The loop slope parameter, α , of such FePt film approached 1.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: The effects of interlayer coupling on switching field and magnetization reversal mechanism of Co <sub>72</sub> Pt <sub>28</sub>– SiO <sub>2</sub>( hard )/ Co – SiO <sub>2</sub>( soft ) exchange coupled media were investigated. The soft layer, with thickness less than the domain wall width, followed domain wall assisted switching mechanism for direct interlayer coupling between the hard and soft layers. It was effective in significantly reducing the switching field. The strength of interlayer coupling between the hard and soft layers was controlled by inserting the Pt intermediate layer between them. The reduced interlayer coupling led to independent switching of the hard and the soft layer and was ineffective in reducing the switching field.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: Fe Pt –X ( X= C , Ti O <sub>2</sub> , Ta <sub>2</sub> O <sub>5</sub> ) nanocomposite films were deposited on Mg O / Cr Ru /glass substrates at 350 ° C by magnetron cosputtering. The comparison investigations on the magnetic properties and microstructure of Fe Pt –X films with various dopants were conducted. All Fe Pt –X films showed (001) preferred orientation and oxide dopants promoted the formation of magnetically soft fcc FePt phase. With 15 vol % C doping, FePt–C film with columnar grains of 7.5 nm was obtained and the out-of-plane coercivity measured at room temperature was as high as 14.4 kOe . The increase in carbon volume fraction to 20% caused the formation of two-layer structure, whereas for the 20 vol % Ti O <sub>2</sub> and Ta <sub>2</sub> O <sub>5</sub> doping, the columnar structure of the FePt films remained and the corresponding grain sizes were 5 and 10 nm , respectively. Ta <sub>2</sub> O <sub>5</sub> doping showed better grain isolation than the others. The out-of-plane coercivities of Fe Pt – Ti O <sub>2</sub> and Fe Pt – Ta <sub>2</sub> O-
<sub>5</sub> films were 7.5 and 8.8 kOe , respectively.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: The FePt:C films with different volume fractions of carbon were epitaxially grown on the CrRu(200) underlayer with Pt and MgO intermediate layers. The magnetic properties and microstructure of these FePt:C films were investigated. The FePt:C films grown on Pt intermediate layer consisted of a continuous layer of FePt, with overlying granular FePt grains. The FePt:C films grown on MgO intermediate layer consisted of a granular FePt:C layer with overlying granular grains. The formation of the overlying granular FePt grains was attributed to carbon diffusion to the surface, which resulted in the second nucleation of FePt. The different interface energy and surface energy of FePt on Pt and MgO intermediate layers caused the formation of initial continuous FePt layer on Pt intermediate layer and initial granular FePt layers on MgO intermediate layer. The out-of-plane coercivity measured at room temperature increased from 10.2 to 19 kOe when C concentrations increased from 0 to 15%. Further increasing the C contents to 20% and 25% caused the decrease of coercivity to 17.2 and 14.8 kOe, respectively. The coercivity of the exchange coupling assisted FePt:C perpendicular media was indeed substantially reduced.
IEEE Transactions on Magnetics 03/2009; · 1.36 Impact Factor
