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15 Jan 2002

Volume 91, Issue 2, pp. 551-892

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Effect of Cr concentration gradient on the intergranular exchange in CoCr(Ta,Pt) thin films

Bogdan Valcu and H. Neal Bertram

J. Appl. Phys. 91, 764 (2002); http://dx.doi.org/10.1063/1.1413492 (8 pages) | Cited 2 times

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Intergranular exchange in CoCr-alloy polycrystalline thin films utilized for longitudinal recording media is analyzed in terms of details of their chemical composition. Two neighboring interacting grains are modeled by a linear “atomic” chain extending from the center of one grain to the center of another. The composition at each spin site determines the interspin exchange interaction. Thermal fluctuations are included via mean field theory and they yield spacial variations of the saturation magnetization and the crystal anisotropy that differ from the bulk properties. Equilibrium spin configurations for the linear chain are obtained for different Cr concentrations at the grain boundary and for different temperatures. Chromium segregation at the boundary is confirmed to be the mechanism for grain decoupling. An effective exchange parameter, assuming uniformly magnetized grains like those in large-scale micromagnetic simulations, is determined. This parameter decreases significantly with increasing temperature and increases slightly with relative anisotropy axis orientation. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.50.Cc Other ferromagnetic metals and alloys

Influence of stress on nucleation field of CoCrPt perpendicular media

C. L. Platt, J. K. Howard, A. G. Roy, and D. E. Laughlin

J. Appl. Phys. 91, 772 (2002); http://dx.doi.org/10.1063/1.1423395 (3 pages) | Cited 3 times

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The influence of stress on the nucleation field was investigated for CoCrPt perpendicular media grown on a Ta/Hf buffer layer. The nucleation field increased to −1.5 kOe (second quadrant) following postdeposition annealing of a sample at 232 °C in air for 1 h. The residual in-plane stress for the annealed film was tensile, and in-plane x-ray diffraction showed that the a0 lattice parameter increased with increasing annealing time. It is believed that the change in stress was due to surface oxidation of the CoCrPt film. The increased stress anisotropy perpendicular to the plane of the film resulted in the increased nucleation field. © 2002 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Ss Magnetic recording materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Cc Other ferromagnetic metals and alloys

Influence of the crystal structure and chemical order on the magnetic and magneto-optical properties of equiatomic CoPt alloy

L. Uba, S. Uba, O. Horpynyuk, V. N. Antonov, and A. N. Yaresko

J. Appl. Phys. 91, 775 (2002); http://dx.doi.org/10.1063/1.1425430 (5 pages) | Cited 10 times

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The influence of the structure-dependent electronic effects on the magnetic, magneto-optical (MO), and anisotropic properties of equiatomic CoPt alloy was modeled with the use of fully relativistic linear-muffin-tin-orbital calculations. We found large differences between the MO spectra of the alloy of the AuCu (L11) and CuPt (L10) superlattice type structures, as well as a strong sensitivity of the spectra on the degree of chemical order. Very good agreement between the experimental and theoretical spectra for both a partially ordered and a fully disordered alloy, modeled by a Monte Carlo simulation, is found, demonstrating the applicability of the theoretical approach. © 2002 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Rf Relativistic effects
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.20.Gj Other metals and alloys

Lorentz transmission electron microscopy and magnetic force microscopy characterization of NiFe/Al-oxide/Co films

Andrew C. C. Yu, Chester C. H. Lo, Amanda K. Petford-Long, David C. Jiles, and Terunobu Miyazaki

J. Appl. Phys. 91, 780 (2002); http://dx.doi.org/10.1063/1.1427142 (5 pages) | Cited 2 times

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Magnetization reversal process of NiFe/Al-oxide/Co junction films was observed directly using Lorentz transmission electron microscopy (LTEM) and magnetic force microscopy (MFM). In situ magnetizing experiments performed in both LTEM and MFM were facilitated by a pair of electromagnets, which were mounted on the sample stages. A two-stage magnetization reversal process for the junction film was clearly observed in LTEM with NiFe magnetization reversed first via domain wall motion followed by Co magnetization reversal via moment rotation and domain wall motion. Reversal mechanism and domain characteristics of the NiFe and Co layers showed very distinctive features. The magnetization curve of the junction film measured using alternating gradient force magnetometry showed a nonzero slope at the antiparallel magnetization configuration region, which implies that magnetization directions of the NiFe and Co layers were not exactly antiparallel due to Co moment rotation existed in that region. After the magnetization reversal of the Co was complete, MFM images revealed some magnetic contrast, which suggests that an out-of-plane magnetization component remained in the Co layer. Such magnetic contrast disappeared at higher magnetic fields when the Co moments further rotated and aligned parallel to the applied field direction. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Jk Magnetization reversal mechanisms
68.37.Rt Magnetic force microscopy (MFM)
68.37.Lp Transmission electron microscopy (TEM)

Coexistence of paramagnetic-charge-ordered and ferromagnetic-metallic phases in La0.5Ca0.5MnO3 evidenced by electron spin resonance

F. Rivadulla, M. Freita-Alvite, M. A. López-Quintela, L. E. Hueso, D. R. Miguéns, P. Sande, and J. Rivas

J. Appl. Phys. 91, 785 (2002); http://dx.doi.org/10.1063/1.1426241 (4 pages) | Cited 30 times

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Throughout a complete electron spin resonance (ESR) and magnetization study of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated state established in this compound below T∼210 K. Between TN⩽T⩽TC, the ESR spectra shows two lines characteristic of two different magnetic phases. From the resonance field (Hr) derived for each line, we argue that the incommensurate-charge-ordering phase (ICO) which coexists with ferromagnetic–metallic (FMM) clusters in this temperature interval, is mainly paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a relatively small field, which suggests that the internal energy associated with those phases is very similar. Below TN, there is an appreciable ferromagnetic (FM) contribution to the magnetization and the ESR spectra indicates the presence of FM clusters in an antiferromagnetic matrix (canted). Our results show that ESR could be a very useful tool to investigate the nature of the phase-separated state now believed to play a fundamental role in the physics of mixed valent manganites. © 2002 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
76.30.-v Electron paramagnetic resonance and relaxation
64.75.-g Phase equilibria
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.28.+d Narrow-band systems; intermediate-valence solids
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena

Effect of Fe doping on the magnetotransport properties in Nd0.67Sr0.33MnO3 manganese oxides

Y. L. Chang, Q. Huang, and C. K. Ong

J. Appl. Phys. 91, 789 (2002); http://dx.doi.org/10.1063/1.1421044 (5 pages) | Cited 13 times

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We have performed magnetic and transport measurements on a series of Nd0.67Sr0.33Mn1−xFexO3 polycrystalline compounds with x=0.0, 0.05, 0.10, and 0.15. For the Fe-undoped Nd0.67Sr0.33MnO3 (NSMO) materials, a magnetoresistance (MR) as high as ∼33% was observed at the metal–insulator transition temperature, Tp=273 K, in a magnetic field of 10 kOe. Fe substitution in Mn sites leads to a reduction in Tp and an increase in the overall MR. A 10% Fe contribution increases the MR up to about 65% and lowers Tp to 88 K. The calculated magnetic moment at 5 K and an applied field at 9 T for the parent NSMO is 4.21 μB and decreases continuously with an increasing amount of iron added. It was found that with the same amount of Fe doping, the Curie temperature, TC, decreases much faster in the Nd-based system than in the corresponding La-based system. The enhanced colossal magnetoresistance and the suppression of ferromagnetism observed in this compound can be interpreted as due to the weakening of the double exchange mechanism by Fe3+ ions, which causes the localization of the hopping electrons. © 2002 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
72.60.+g Mixed conductivity and conductivity transitions
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
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