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7 May 2013

Volume 113, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 174302 (2013); http://dx.doi.org/10.1063/1.4798262 (4 pages)

Yuichiro Kurokawa, Takehiko Hihara, and Ikuo Ichinose
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back to top Ultra-thin and Multi-layer Films

Influence of Pt spacer thickness on the domain nucleation in ultrathin Co/Pt/Co trilayers

R. D. Shull, Y. L. Iunin, Y. P. Kabanov, V. I. Nikitenko, O. V. Skryabina, and C. L. Chien

J. Appl. Phys. 113, 17C101 (2013); http://dx.doi.org/10.1063/1.4793703 (3 pages)

Online Publication Date: 27 February 2013

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The effect of varying the interlayer coupling between two 0.6 nm thick Co layers with perpendicular anisotropy on their magnetic ground state and the domain nucleation processes during a field reversal was studied. A transition from out-of-plane to in-plane anisotropy was revealed as the Pt spacer thickness decreased below 1.6 nm. For Pt thicknesses in the range of 1.6–5.4 nm, domain nucleation occurred in both Co layers in a correlated manner, and subsequent motion of the domain walls proceeded as though bound together. A transition to uncorrelated domain nucleation and independent wall motion was observed at Pt thicknesses above 5.4 nm. Both conventional and “asymmetrical” domain nucleation centers were observed in the whole range of platinum spacer thicknesses.
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75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Static and dynamic properties of Fibonacci multilayers

L. D. Machado, C. G. Bezerra, M. A. Correa, C. Chesman, J. E. Pearson, and A. Hoffmann

J. Appl. Phys. 113, 17C102 (2013); http://dx.doi.org/10.1063/1.4794190 (3 pages)

Online Publication Date: 6 March 2013

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We theoretically investigate static and dynamic properties of quasiperiodic magnetic multilayers. We considered identical ferromagnetic layers separated by non-magnetic spacers with two different thicknesses chosen based on the Fibonacci sequence. Using parameters for Fe/Cr, the minimum energy was determined and the equilibrium magnetization directions found were used to calculate magnetoresistance curves. Regarding dynamic behavior, ferromagnetic resonance (FMR) curves were calculated using an approximation known from the literature. Our numerical results illustrate the effects of quasiperiodicity on the static and dynamic properties of these structures.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.30.Gw Magnetic anisotropy

Structural and magnetic properties in Heusler-type ferromagnet/antiferromagnet bilayers

N. Fukatani, K. Inagaki, T. Miyawaki, K. Ueda, and H. Asano

J. Appl. Phys. 113, 17C103 (2013); http://dx.doi.org/10.1063/1.4794133 (3 pages)

Online Publication Date: 7 March 2013

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The structure and magnetic properties of Heusler ferromagnet/antiferromagnet (FM/AFM) bilayers were investigated. Structural characterization revealed that Fe2CrSi/Ru2MnGe bilayers were epitaxially grown with an L21 ordered structure when the Ru2MnGe growth temperature was 573 K. The magnetization curve indicates that exchange bias occurs in the Fe2CrSi/Ru2MnGe bilayers at 77 K. The appearance of an exchange-anisotropy field Hex depends on the growth of Ru2MnGe layer, indicating that the exchange bias originates from the epitaxial Fe2CrSi/Ru2MnGe interface. The exchange anisotropy energy Jk of the Fe2CrSi/Ru2MnGe and Co2MnGe/Ru2MnGe bilayer systems appears to follow a Heisenberg-like exchange coupling model. This suggests that the Cr and Mn interface atoms in the FM layers play significant roles in exchange coupling in the Fe2CrSi/Ru2MnGe and Co2MnGe/Ru2MnGe bilayer systems, respectively.
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75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.at Other materials
75.30.Et Exchange and superexchange interactions

Using different Mn-oxides to influence the magnetic anisotropy of FePt in bilayers with little change of the exchange bias field

K.-W. Lin, C. Shueh, C.-H. Liu, E. Skoropata, T.-H. Wu, and J. van Lierop

J. Appl. Phys. 113, 17C104 (2013); http://dx.doi.org/10.1063/1.4794132 (3 pages)

Online Publication Date: 8 March 2013

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We have investigated the exchange coupling between a bottom FePt thin film layer capped with different Mn-oxides. Results have shown that the magnetization reversal of the soft FePt layer is influenced strongly by the capped Mn-oxide layer (Mn, MnO, and Mn3O4), as revealed by the enhanced coercivities. Typical temperature dependent magnetization between zero-field cooled (ZFC) and field cooled (FC) scans was observed in the Mn-oxide (8%O2/Ar)/FePt bilayer that exhibited a blocking temperature (TB ∼ 120 K) close to the Nèel temperature, TN, of MnO. However, the Mn/FePt bilayer exhibited unusual temperature dependent of M vs. T, implying that intermixing between Mn and FePt interfaces formed an AF FeMn that may have enabled a high irreversibility temperature (Tirr. ∼ 400 K) compared to almost identical ZFC and FC curves from weaker exchange coupling between FePt and the Mn3O4 created with 21 and 30%O2/Ar deposition conditions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Multilayer nanogranular films (Co40Fe40B20)50(SiO2)50/α-Si:H and (Co40Fe40B20)50(SiO2)50/SiO2: Magnetic properties

S. V. Komogortsev, E. A. Denisova, R. S. Iskhakov, A. D. Balaev, L. A. Chekanova, Yu. E. Kalinin, and A. V. Sitnikov

J. Appl. Phys. 113, 17C105 (2013); http://dx.doi.org/10.1063/1.4794361 (3 pages)

Online Publication Date: 8 March 2013

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Magnetic properties of multilayers, consisting of nanogranular (Co40Fe40B20)50(SiO2)50 layers as thin as magnetic granule diameter alternating the α-Si:H or SiO2 layers and the single layer film (Co40Fe40B20)50(SiO2)50 with the thickness much larger than the magnetic granule diameter are reported and compared. The thick single layer film is ferromagnetic but the multilayer film with the ultrathin granular layers and SiO2 spacer is superparamagnetic. This is interpreted as the result of increasing percolation threshold in the 2D granular media above 50% concentration of magnetic granules in the multilayer with the nonmagnetic and dielectric SiO2 spacer. The multilayer with the α-Si:H spacer is superparamagnetic at 300 K but it becomes ferromagnetic, when temperature is below 250 K. It is assumed to be resulted from the exchange interaction of magnetic granules through the semiconductor α-Si:H layers. The value of exchange interaction through the semiconductor spacer is estimated.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films

Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

M. Belmoubarik, T. Nozaki, H. Endo, and M. Sahashi

J. Appl. Phys. 113, 17C106 (2013); http://dx.doi.org/10.1063/1.4794875 (3 pages)

Online Publication Date: 8 March 2013

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Deposition of ZnO thin films on a ferromagnetic metallic buffer layer (Co3Pt) by molecular beam epitaxy technique was investigated for realization of ZnO-based magnetic tunneling junctions with good quality hexagonal ZnO films as tunnel barriers. For substrate temperature of 600 °C, ZnO films exhibited low oxygen defects and high electrical resistivity of 130 Ω cm. This value exceeded that of hexagonal ZnO films grown by sputtering technique, which are used as tunnel barriers in ZnO-MTJs. Also, the effect of oxygen flow during deposition on epitaxial growth conditions and Co3Pt surface oxidation was discussed.
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73.61.Ga II-VI semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
81.65.Mq Oxidation
68.55.ag Semiconductors

Magnetic stability of ultrathin FeRh films

G. C. Han, J. J. Qiu, Q. J. Yap, P. Luo, D. E. Laughlin, J. G. Zhu, T. Kanbe, and T. Shige

J. Appl. Phys. 113, 17C107 (2013); http://dx.doi.org/10.1063/1.4794980 (3 pages)

Online Publication Date: 21 March 2013

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This paper presents magnetic properties of highly ordered ultrathin FeRh films deposited on Si/SiO wafers with MgO as a buffer layer. The antiferromagnetic to ferromagnetic (FM) transition is observed with a thickness as low as 3 nm. However, as the thickness decreases, the residual magnetization (Mrs) at low temperature increases and the amplitude of the transition decreases. In addition, the transition becomes much broader for the thinner films. This broadening is related to the grain size reduction in the thinner films. The temperature dependence of the magnetization of a highly ordered B2 FeRh film with a thickness of 10 nm was carefully measured as a function of field. The results show that the transition temperature decreases almost linearly with a rate of 0.93 K/kOe (heating) and 0.97 K/kOe (cooling) close to the value for the bulk samples, while Mrs obtained at 100 K increases rapidly at low field and then linearly at a field larger than 10 kOe, which clearly demonstrates that an applied field would induce FM stabilization in ultrathin FeRh films.
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75.70.Ak Magnetic properties of monolayers and thin films
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Cd Deposition by sputtering
68.55.at Other materials

(001) oriented L10 FePt/B4C multilayer thin films on naturally oxidized Si substrate

J. Zhang, H. Ding, S. Q. Li, Q. T. Li, H. B. Wang, Q. Mo, and H. Wang

J. Appl. Phys. 113, 17C108 (2013); http://dx.doi.org/10.1063/1.4795324 (3 pages)

Online Publication Date: 21 March 2013

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(001) oriented FePt/B4C multilayer thin films with high perpendicular coercivity (≥9.7 kOe) were prepared on naturally oxidized Si substrates by magnetron sputtering and thereafter annealing. Effect of FePt layer thickness on the texture parameter of the (001) orientation, chemical ordering, and magnetic properties has been studied. It was found that the texture parameter of (001) orientation increases while the degree of chemical ordering decreases with the decrease of FePt layer thickness. The coercivity drops with the decrease of layer thickness due to the low degree of chemical ordering. The results of δM plots analysis show that intergrain exchange coupling action weakens in response to the decrease of layer thickness and thus decreases the remanence ratio.
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81.15.Cd Deposition by sputtering
68.55.jm Texture
68.65.Ac Multilayers
75.50.Ss Magnetic recording materials
75.50.Vv High coercivity materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Ion irradiation induced enhancement of out-of-plane magnetic anisotropy in ultrathin Co films

P. Mazalski, Z. Kurant, A. Maziewski, M. O. Liedke, J. Fassbender, L. T. Baczewski, and A. Wawro

J. Appl. Phys. 113, 17C109 (2013); http://dx.doi.org/10.1063/1.4798805 (3 pages)

Online Publication Date: 3 April 2013

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Ga+ or He+ irradiated MBE grown ultrathin films of sapphire/Pt/Co(dCo)/Pt(dPt) were studied using polar Kerr effect in wide ranges of both cobalt dCo and platinum dPt thicknesses as well as ion fluences F. Two branches of increased magnetic anisotropy and enhanced Kerr rotation angle induced by Ga+ or He+ irradiation are clearly visible in two-dimensional (dCo, LogF) diagrams. Only Ga+ irradiation induces two branches of out-of-plane magnetization state.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.jd Thickness

Microstructure study of CoPt thin film with phase change from A1 → L11 → A1 → L10

An-Cheng Sun and Chuan-Fa Huang

J. Appl. Phys. 113, 17C110 (2013); http://dx.doi.org/10.1063/1.4799526 (3 pages)

Online Publication Date: 8 April 2013

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In this study, 50-nm-thick CoPt film was sputtered on MgO(111) substrate at substrate temperature (Ts) from room temperature (RT) to 750 °C. Within the temperature range, the phase evolves in the sequence of A1 (disordered) at RT, L11 (ordered), A1, and L10 (ordered) at 750 °C. L11-ordering occurred in the range of 250 °C ≦ Ts ≦ 500 °C induces strong perpendicular magnetic anisotropy. Microstructure results indicate that the CoPt grain size increases gradually from about 10 to 50 nm as Ts increases from RT to 600 °C. Grain size significantly increases to larger than 70 nm as Ts > 600 °C, which is attributed to the occurrence of L10-ordering. Further increase Ts to 750 °C, isotropic L10-(111) textured CoPt forms with a higher Hc of 5.0 kOe. Detailed discussion of relation between magnetic behaviors and microstructure is given.
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75.70.Ak Magnetic properties of monolayers and thin films
64.70.kd Metals and alloys
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
75.30.Gw Magnetic anisotropy

Magnetic anisotropy and thermal stability study of perpendicular Co/Ni multilayers

Guangzhong Wang, Zongzhi Zhang, Bin Ma, and Q. Y. Jin

J. Appl. Phys. 113, 17C111 (2013); http://dx.doi.org/10.1063/1.4799524 (3 pages)

Online Publication Date: 10 April 2013

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The perpendicular magnetic anisotropy (PMA) and thermal stability of Ta (3.0 nm)/Cu (tCu)/[Co (0.29 nm)/Ni (0.65 nm)]N/Ta (3.0 nm) multilayers are investigated with various Cu thicknesses (tCu) and Co/Ni periodic numbers (N). A relatively thick Cu seed layer and a suitable Co/Ni repetition number benefit the PMA with larger coercivity and remanence ratio. But the magnetic hysteresis loop for the structure with N in excess of 10 exhibits a bow-tie shape due to the formation of multi-domains, which may cause a significant drop of the remanence ratio. The post-annealing experiments show that the thermal stability of PMA increases with increasing N. In addition to the intermixing of Co and Ni atoms at interfaces, we consider that the diffusion of nonmagnetic atoms into the magnetic layers is also responsible for the PMA decay with increasing annealing temperature.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.70.Ak Magnetic properties of monolayers and thin films

Crossover between in-plane and perpendicular anisotropy in Ta/CoxFe100-x/MgO films as a function of Co composition

Sung-Min Ahn and G. S. D. Beach

J. Appl. Phys. 113, 17C112 (2013); http://dx.doi.org/10.1063/1.4799779 (3 pages)

Online Publication Date: 10 April 2013

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Interfacial magnetic anisotropy in Ta/CoxFe100-x (CoFe)/MgO films for alloy compositions spanning pure Co to pure Fe has been studied in order to investigate the role of chemical composition in the onset of perpendicular magnetic anisotropy at the CoFe/MgO interface. Out-of-plane magnetization is not observed in Ta/Fe/MgO (x = 0) and Ta/Co/MgO (x = 100), for all ranges of CoFe thickness (t), but a t-dependent crossover between in-plane and out-of-plane anisotropy is found for x = 20, 50, and 80. Interestingly, effective magnetic anisotropy Ku as well as interfacial anisotropy Ki are maximized for Co50Fe50 at a fixed t = 0.8 nm. The results suggest that the degree of filling of valence bands in the CoFe adjacent to the interface, which determines the relative population of the anisotropic d-bands, plays an important role in the interfacial anisotropy brought on by CoFe-O hybridization at the metal/oxide interface.
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75.30.Gw Magnetic anisotropy
82.80.-d Chemical analysis and related physical methods of analysis
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films

Nonlinear temperature dependent nucleation field in perpendicular exchange spring typed magnetic tunnel junctions

Yi Wang, D. Le Roy, Jun Jiang, Xiaolu Yin, H. X. Wei, S. H. Liou, and X. F. Han

J. Appl. Phys. 113, 17C113 (2013); http://dx.doi.org/10.1063/1.4801406 (3 pages)

Online Publication Date: 11 April 2013

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The nonlinear temperature dependence of nucleation field (Hn) of [Co/Pt]n multilayer based perpendicular magnetic tunnel junction stacks with wedged Co60Fe20B20 insertion layers is reported. When temperature decreases, the tilted spins away from perpendicular direction near Co60Fe20B20/AlOx interface play dominating role to promote the nucleation process and lower Hn value and even change the sign of Hn. By taking advantage of high temperature annealing under high perpendicular magnetic field, this nonlinear behavior and sign of Hn could be manipulated. The understanding of temperature dependent properties in such system is important for spintronics applications, such as in memory and spin oscillators.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments

Magnetic anisotropy in Fe films epitaxied by thermal deposition and pulse laser deposition on GaAs(001)

X. Xiao, J. H. Liang, Y. Huo, J. Zhu, G. Chen, and Y. Z. Wu

J. Appl. Phys. 113, 17C114 (2013); http://dx.doi.org/10.1063/1.4798819 (3 pages)

Online Publication Date: 12 April 2013

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The in-plane magnetic anisotropy of Fe films fabricated with thermal deposition (TD) and pulse laser deposition (PLD) techniques on GaAs(001) substrate was studied quantitatively. The volume anisotropy in TD Fe film is attributed to the constant strain anisotropy, supported by reflection high-energy electron diffraction analysis. The PLD growth was found to deeply influence the interface anisotropy at Fe/GaAs interface even through a 30 ML Fe TD underlayer. The volume anisotropy was found to exist in TD Fe film even grown on top of a PLD film. Our study indicates that the uniaxial magnetic anisotropy in Fe/GaAs(001) system can be controlled by a combination of TD and PLD growth.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
75.30.Gw Magnetic anisotropy

Tunable resonant properties of perpendicular anisotropy [Co/Pd]/Fe/[Co/Pd] multilayers

Jian Dou, Michael J. Pechan, E. Shipton, N. Eibagi, and E. E. Fullerton

J. Appl. Phys. 113, 17C115 (2013); http://dx.doi.org/10.1063/1.4801641 (3 pages)

Online Publication Date: 16 April 2013

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We describe the static and dynamic magnetic behaviors of Fe films (thicknesses 2, 4, and 6 nm) sandwiched between Co/Pd multilayers with strong perpendicular magnetic anisotropy. Out-of-plane measurements of both magnetization and ferromagnetic resonance confirm well-defined Fe layer response modified by large perpendicular exchange field arising from the coupling with the Co/Pd. The field/frequency dispersion is linear for all samples with field intercepts increasing with Fe layer thickness. Analysis in terms of shape anisotropy and interfacial exchange model yields a large out-of-plane interfacial coupling of ∼3.0–3.7 erg/cm2 that is mediated by the coupling across thin Pd layers. The value of this interface exchange is also shown to be tunable with interfacial Pd thickness.
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81.05.Bx Metals, semimetals, and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Annealing effect and under/capping layer study on Co/Ni multilayer thin films for domain wall motion

En Yang, Vincent M. Sokalski, Matthew T. Moneck, David M. Bromberg, and Jian-Gang Zhu

J. Appl. Phys. 113, 17C116 (2013); http://dx.doi.org/10.1063/1.4795720 (3 pages)

Online Publication Date: 17 April 2013

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Co/Ni multilayer structure with Perpendicular Magnetic Anisotropy (PMA) is considered to be one of the most promising film structures for current-driven domain wall motion. In this work, the field annealing effect on Co/Ni multilayer films with different underlayers is studied. The annealing temperature ranges from 250 °C to 375 °C. The effect of Pt capping layer is also investigated. It was found that the annealing process influences magnetic properties of Co/Ni multilayers with different underlayers differently. For Co/Ni multilayers with Ni underlayer, no PMA is observed in the as-deposited state, but they become perpendicular after annealing, and the effective perpendicular magnetic anisotropy (Keff) increases linearly with annealing temperature. The origin of the Keff increase is discussed. For Co/Ni multilayers with Pt underlayers, large PMA is observed for as-deposited films; however, Keff decreases after annealing. The effects of interfacial lattice mismatch, roughness, and impurities to surface anisotropy are discussed. It was also found that with Pt underlayer, the presence of a thin Pt capping layer is crucial for Co/Ni multilayers to cancel the in-plane Rashba field and stabilize the current-driven domain wall motion.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
81.40.Gh Other heat and thermomechanical treatments
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Metastable fcc-Fe film epitaxially grown on Cu(100) single-crystal underlayer

Mitsuru Ohtake (大竹充), Kohei Shimamoto (島本晃平), and Masaaki Futamoto (二本正昭)

J. Appl. Phys. 113, 17C117 (2013); http://dx.doi.org/10.1063/1.4801404 (3 pages)

Online Publication Date: 18 April 2013

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Fe film of 40 nm thickness is prepared on fcc-Cu(100) single-crystal underlayer at room temperature by ultra-high vacuum molecular beam epitaxy. The film growth and the detailed structure are investigated by reflection high-energy electron diffraction, cross-sectional high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). An Fe single-crystal with metastable fcc structure nucleates on the underlayer. The HR-TEM shows that fcc lattice is formed from the Fe/Cu interface up to the film surface. A large number of misfit dislocations are introduced around the Fe/Cu interface due to an accommodation of lattice mismatch. Dislocations exist up to the film near surface. The lattice constant is estimated by XRD to be a = 0.3607 nm. The film shows a ferromagnetic property, which reflects the property of fcc-Fe crystal with high-spin ferromagnetic state.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.at Other materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films

The intrinsic temperature dependence and the origin of the crossover of the coercivity in perpendicular MgO/CoFeB/Ta structures

Meng-Chiau Tsai, Chih-Wei Cheng, C. C. Tsai, and G. Chern

J. Appl. Phys. 113, 17C118 (2013); http://dx.doi.org/10.1063/1.4799518 (3 pages)

Online Publication Date: 19 April 2013

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A collapse of tunnel magneto resistance (TMR) in the perpendicular magnetic configuration of CoFeB/MgO/CoFeB tunnel junction at high annealing temperatures has been reported recently [Ikeda et al., Nature Mater. 9, 721 (2010)]. This observation indicates that not only the temperature-dependent magnetic characterization is important in a pseudo-spin valve type devices but also implies an asymmetrical dependence on the magnetic behavior between the top and bottom CoFeB layers. In this report, we have measured a series of MgO/CoFeB/Ta with different thicknesses of CoFeB (1.0−1.7 nm) and Ta cap layer (1–5 nm) and found a intrinsic dependence of magnetic coercivity of Hc = Hco[1−(T/TB)1/2], where Hco is Hc at 0 K and TB is the blocking temperature, for all films. A systematic study shows that Hco varies in the range of 2500 Oe−250 Oe with a rough inverse linear dependence on CoFeB layer thickness. The TB for all films except the thinnest one (1.0 nm) is in a smaller range of 280–300 K, but drops to 150 K for the thinnest film. The corresponded particle sizes are estimated ∼30 nm. The origin of the microstructure of the present films is probably related to the defect at the interface and formed during the post annealing process. A control of the collapse of the TMR through the cap Ta layer thickness will be discussed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Nt Magnetic annealing and temperature-hysteresis effects
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Scaling of the anomalous Hall effect in perpendicular CoFeB/Pt multilayers

S. B. Wu, X. F. Yang, S. Chen, and T. Zhu

J. Appl. Phys. 113, 17C119 (2013); http://dx.doi.org/10.1063/1.4801335 (3 pages)

Online Publication Date: 19 April 2013

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The anomalous Hall effect (AHE) in the perpendicular CoFeB/Pt multilayers has been investigated. It is found that AHE comes from a small side jump contribution combining with a large skew scattering contribution, which is in contradiction to the conventional perpendicular Co/Pt multilayers. Moreover, the contribution of skew scattering is enhanced with the increasing number of the CoFeB/Pt bilayer.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Packings of Os layers for the development of L10 order of FePt in nanoscale [Os-FePt]n multilayer systems

T. T. Su, Ching-Hung Hsiao, Shen-Chuan Lo, Wen Ouyang, Tzu-Yuan Li, H. Ouyang, and Y. D. Yao

J. Appl. Phys. 113, 17C120 (2013); http://dx.doi.org/10.1063/1.4800985 (3 pages)

Online Publication Date: 23 April 2013

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The element osmium (Os), with high melting and boiling points, plays a crucial role in the development of the L10 order for FePt in [Os(5 nm)/FePt(25 nm)]4 and [Os(1 nm)/FePt(5 nm)]20 systems. The large mismatches of lattice constants between Os and FePt, with specific epitaxial relations, induce a great strain in the [Os(5 nm) /FePt(25 nm)]4 system with fixed total thicknesses for the FePt and Os layers. Due to this large strain effect, the L10 order in a FePt structure can be enhanced through an application of stressing along the c axis for the face-centered cubic structure, which results in a higher coercivity. However, a smaller degree of average strain was observed in the 5 nm-thickness FePt system due to the existence of pinholes.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
64.70.dj Melting of specific substances
64.70.fh Boiling and bubble dynamics
68.65.Ac Multilayers
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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