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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Evolution of stress with L10 ordering in FePt and FeCuPt thin films

K. W. Wierman, C. L. Platt, J. K. Howard, and F. E. Spada

J. Appl. Phys. 93, 7160 (2003); http://dx.doi.org/10.1063/1.1555893 (3 pages) | Cited 29 times

Online Publication Date: 9 May 2003

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The evolution of stress in 50 nm FexPt1−x (x=0.41, 0.43, 0.49, 0.52, and 0.56) sputtered films was monitored in situ as a function of the temperature. In the as-deposited state, films have a disordered face-centered-cubic (fcc) structure with a strong (111) fiber texture and 685–978 MPa compressive stress. Below 200 °C, thermal expansion of the FexPt1−x fcc lattice produced an initial increase in residual in-plane compressive stress. Above 250 °C, a transition to a low stress state was observed, with the relaxation in the Fe0.52Pt0.48 film showing stronger temperature dependence. Comparisons of stress to a sputtered film of Fe0.35Cu0.15Pt0.5 indicate a faster transition rate to the low stress state can be achieved with the addition of Cu. In situ high temperature x-ray diffraction measurements show a decrease in (111) d spacing with an increase in temperature, and are consistent with the changes observed in the residual stress measurements. The large stress transition appears to arise from changes in the fcc phase prior to L10 phase transformation, because a substantial increase in film coercivity appears only after the transition to the low stress state has been completed. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
75.50.Ss Magnetic recording materials
61.72.Cc Kinetics of defect formation and annealing
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic and magneto-optical properties of ultrathin Fe50Pt50 films with Ag layers inserted

Zhengang Zhang, Kyongha Kang, and Takao Suzuki

J. Appl. Phys. 93, 7163 (2003); http://dx.doi.org/10.1063/1.1540039 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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Ultrathin Fe50Pt50 (2 nm)/Ag (x nm)/Fe50Pt50 (2 nm)/Ag (x nm)/Fe50Pt50 (2 nm) multilayer films are deposited onto a MgO (100) substrate by laser ablation and ex situ annealed at 630 °C for 15 min, with the Ag inserted layer changing in thickness from x=0 to 4 nm. (001) textured, highly ordered (ordering parameter S∼0.9) FePt films are obtained when x⩾1 nm. Both the perpendicular coercivity and anisotropy field (Hk) show a dependence on the inserted Ag layer thickness, with a peak appearing at x=1 nm. In the sample with the highest Hk, the rotational mode contributes to magnetization reversal, while in lower Hk samples domain wall motion plays a dominant role. The polar Kerr spectroscopy and optical constants of these samples are measured with photon energy in the range of 1.4–6.8 eV. The feature of diagonal dielectric elements at around 3.8 eV reveals the Ag plasma resonance effect. However, no obvious Kerr effect enhancement at the Ag plasma edge is observed. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.65.Ac Multilayers
81.15.Fg Pulsed laser ablation deposition
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.20.Ls Magneto-optical effects
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Size effect on the ordering of FePt granular films

Y. K. Takahashi, T. Ohkubo, M. Ohnuma, and K. Hono

J. Appl. Phys. 93, 7166 (2003); http://dx.doi.org/10.1063/1.1555895 (3 pages) | Cited 71 times

Online Publication Date: 9 May 2003

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We have investigated the A1→L10 ordering process of FePt granular films with different particle sizes. Although FePt particles larger than ∼7 nm ordered by annealing at 600 °C, the ordering did not proceed when the particle size was smaller than ∼4 nm in diameter. This suggests that there is a size dependence on the ordering of FePt particles. Calculation of the Helmholtz free energy using the Lennard-Jones potential suggested that Tc decreases below the annealing temperature when the particle size is decreased to a few nanometers suggesting that experimental observation is physically feasible. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials

Magnetic properties of FePt and FePt–Al2O3 granular films by post annealing

M. Matsumoto, A. Morisako, and N. Katayama

J. Appl. Phys. 93, 7169 (2003); http://dx.doi.org/10.1063/1.1543858 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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FePt and FePt–Al2O3 alloy thin films were prepared by rf magnetron sputtering system, then post annealed in vacuum. The as-deposited films were in disordered state and the ordered L10 structure was obtained by post annealing. The temperature for L10 structure of FePt and FePt–Al2O3 films was about 400 and 550 °C, respectively. The effect of film thickness on magnetic properties was studied. The coercivity decreased rapidly from 8 to 1.5 kOe at the thickness below 10 nm for the FePt L10 films. The decrease of coercivity is due the diffusion and compositional deviation. The surface roughness is as low as 0.3 nm for FePt–Al2O3 films with coercivity of about 3.3 kOe. © 2003 American Institute of Physics.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.50.Ss Magnetic recording materials
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.30.Gw Magnetic anisotropy

Fabrication and characterization of ordered FePt nanoparticles

Y. H. Huang, Y. Zhang, G. C. Hadjipanayis, and D. Weller

J. Appl. Phys. 93, 7172 (2003); http://dx.doi.org/10.1063/1.1540040 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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Ordered FePt nanoparticles with unique magnetic properties were obtained by direct deposition of FePt and C onto heated substrates at temperature above 450 °C. The FePt particle sizes were controlled in the range from a few nanometers to 20 nm by adjusting the sputtering time from both the FePt and C targets. The tiny FePt nanoparticles (less than 3 nm) showed superparamagnetic behavior at room temperature. However, larger particles showed huge coercivities at room temperature (23 and 34 kOe for particles with average sizes of around 8 and 15 nm, respectively). For a certain FePt to C ratio, the films can show strong perpendicular anisotropy which is favorable for high density recording media. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Wx Nanopowders
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.-w Structure of nanoscale materials
81.15.Cd Deposition by sputtering
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy

Formation of FePt nanoparticles in annealed FePt/C multilayers

Y. Zhang, J. Wan, M. J. Bonder, G. C. Hadjipanayis, and D. Weller

J. Appl. Phys. 93, 7175 (2003); http://dx.doi.org/10.1063/1.1558232 (3 pages) | Cited 16 times

Online Publication Date: 9 May 2003

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The formation of FePt nanoparticles by annealing FePt/C multilayer in the range of 600–800 °C was studied. During annealing at 700 °C, the coercivity of FePt (5 Å)/C (5 Å) sample increases from 0.2 to 6 kOe after 2 min of annealing, reaching 14.5 kOe after 1 h, while the coercivity of FePt (5 Å)/C (20 Å) sample shows a much slower change with annealing, exhibiting a value of 3.5 kOe after 1 h of annealing. Transmission electron microscopy results did not show a layer structure in as-deposited 5 Å/5 Å samples, and a clear superlattice reflection was observed in 5 Å/5 Å samples subjected to 2 min of annealing, indicative of the L10 fct phase. The degree of atomic ordering of the fct structure increases with further annealing. After 1 h of annealing, the 5 Å/5 Å samples show aggregates of particles with a well-ordered structure and a wide particle size distribution. In the as-deposited 5 Å/20 Å sample, a layer structure was observed with a uniform particle size distribution. After 5 min annealing at 700 °C, the layers are completely broken with the appearance of weak superlattice reflections. Both particle size and degree of atomic ordering increase slowly with further annealing in the 5 Å/20 Å sample. After 1 h annealing, isolated particles were observed with an average particle size of 6 nm. Depositing thicker carbon layers appear to restrict the growth of particles and delay the onset of atomic ordering with annealing. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.Cc Kinetics of defect formation and annealing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Synthesis, chemical ordering, and magnetic properties of self-assembled FePt–Ag nanoparticles

S. S. Kang, D. E. Nikles, and J. W. Harrell

J. Appl. Phys. 93, 7178 (2003); http://dx.doi.org/10.1063/1.1543859 (3 pages) | Cited 42 times

Online Publication Date: 9 May 2003

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[FePt]1−xAgx nanoparticles were chemically synthesized. Self-assembled arrays were characterized by transmission electron microscopy and small angle x-ray diffraction (XRD). Particles were annealed at temperatures from 300 to 500 °C for 30 min and degree of chemical ordering was characterized by large angle XRD and by magnetometry. Compared with pure FePt nanoparticles, additive Ag reduced the A1 to L10 ordering temperature by more than 100 °C. A maximum coercivity of more than 10 kOe was measured for samples with ∼15% Ag annealed at 500 °C, compared with about 2 kOe for samples without Ag. This reduction in required annealing temperature significantly reduces particle coalescence and loss in positional order. XRD measurements suggest that the reduction of the ordering temperature is due to defects and lattice strain introduced by the Ag and the subsequent segregation of the Ag upon annealing, activating the nucleation of the ordered phase. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.Dn Self-assembly
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Cc Kinetics of defect formation and annealing

Studies of switching field and thermal energy barrier distributions in a FePt nanoparticle system

X. W. Wu, H. Zhou, R. J. M. van de Veerdonk, T. J. Klemmer, C. Liu, N. Shukla, D. Weller, M. Tanase, and D. E. Laughlin

J. Appl. Phys. 93, 7181 (2003); http://dx.doi.org/10.1063/1.1540041 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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Dynamic remanent hysteresis loops were measured at several time scales for a L10 ordered Fe45Pt55 nanoparticle array sample. At a fixed percentage of magnetization switched, Sharrock’s formula was applied to obtain both the thermal stability factor and the intrinsic switching field. From the magnetization dependence of the thermal stability factor, the width of the thermal energy barrier distribution was determined to be about 0.30. In comparison with the particle volume distribution width obtained from transmission electron microscopy, the energy barrier width is reduced significantly due to strong interparticle exchange interaction. The magnetization dependence of the intrinsic switching field was used to obtain the intrinsic, i.e., short time, remanent magnetization curves. The intrinsic switching field distribution width was found to be 0.34. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Wx Nanopowders
61.46.-w Structure of nanoscale materials
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys

Thermal stability of self-assembled FePt nanoparticles

T. S. Vedantam, J. P. Liu, H. Zeng, and S. Sun

J. Appl. Phys. 93, 7184 (2003); http://dx.doi.org/10.1063/1.1558233 (3 pages) | Cited 16 times

Online Publication Date: 9 May 2003

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We have produced self-assembled FePt nanoparticles by chemical synthesis and subsequent thermal annealing. The self-assembled samples were annealed in nitrogen or forming gas (95%Ar+5%H2) atmosphere for varying annealing time and temperatures. Thermal annealing above 500 °C resulted in phase transformation of the as-synthesized FePt from the chemically disordered fcc to chemically ordered fct structure which has a high uniaxial magneto-crystalline anisotropy. With increasing annealing temperature, the coercivity and the thermal stability factor KV/kT were found to increase due to improved chemical ordering, irrespective of the annealing atmosphere. For samples annealed at 580 °C for 30 min in forming gas, the maximum coercivity obtained was 6.95 kOe. The samples annealed in forming gas showed higher coercivity and KV/kT values than those annealed in nitrogen for the same annealing time and temperature. We have also measured the Curie temperatures of the FePt nanoparticle assemblies. The Curie temperatures were found to increase with increased annealing time for the samples annealed in nitrogen at 580 °C. © 2003 American Institute of Physics.
Show PACS
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.16.Dn Self-assembly
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.Nd Structural transitions in nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
75.30.Gw Magnetic anisotropy
81.16.Be Chemical synthesis methods

High density magnetic recording on protein-derived nanoparticles

Jay Hoinville, Angus Bewick, David Gleeson, Richard Jones, Oksana Kasyutich, Eric Mayes, Artur Nartowski, Barnaby Warne, Jason Wiggins, and Kim Wong

J. Appl. Phys. 93, 7187 (2003); http://dx.doi.org/10.1063/1.1555896 (3 pages) | Cited 30 times

Online Publication Date: 9 May 2003

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Self-organized Co/Pt nanoparticulate arrays offer a novel approach to fabricating magnetic recording media with the potential for supporting Terabit/in.2 recording densities. Protein-derived Co/Pt nanoparticles are prepared within apoferritin from aqueous reactants, with synthesis conditions controlling grain size, structure, and composition. Smooth films on glass disk substrates are produced by either spin coating or dip coating from aqueous dispersions of the precursor material. Films are typically annealed at 590 °C for 60 min with a 19 kPa (190 mBar) partial pressure of H2 to form the L10 phase. By varying the annealing conditions we are able to produce coercivities in the range of 500–8000 Oe. Electrical testing of Co/Pt nanoparticulate media using a contact test recorder shows that these nanoparticle films are capable of sustaining recording densities of more than 12.6 Gbits/in.2 (143.6 kfci, kilo flux changes per inch). In this article we will present results from finished films with regard to film structure, magnetic properties, and recording capabilities. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
81.16.Fg Supramolecular and biochemical assembly
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.16.Dn Self-assembly
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Fabrication of ordered FePt nanoparticles with a cluster gun

S. Stoyanov, Y. Huang, Y. Zhang, V. Skumryev, G. C. Hadjipanayis, and D. Weller

J. Appl. Phys. 93, 7190 (2003); http://dx.doi.org/10.1063/1.1555898 (3 pages) | Cited 25 times

Online Publication Date: 9 May 2003

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In this study we present a technique to obtain ordered fct FePt particles embedded in a C matrix. FePt nanoparticles are formed inside a high-pressure sputtering cell, called a particle gun (PG), and subsequently deposited on the substrate through a small orifice. These particles have a uniform size distribution with an average particle size that can be controlled in the range of 3–10 nm by adjusting the sputtering cell pressure, power, distance between the magnetron and the orifice, and by using a liquid nitrogen cooling jacket. The particles are converted to the L10 phase as they pass through a specially designed heating stage, attached to the top of the PG, heated by halogen lamps, thus avoiding alloying and oxidation effects. A strong dependence of coercivity on both the particle size and temperature was observed. © 2003 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
64.70.Nd Structural transitions in nanoscale materials
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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