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19 May 2003

Volume 82, Issue 20, pp. 3379-3570

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Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages)

Michael Mück, Christian Welzel, and John Clarke
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Magnetic anisotropy and thermal stability study on FePt nanoparticle assembly

X. W. Wu, K. Y. Guslienko, R. W. Chantrell, and D. Weller

Appl. Phys. Lett. 82, 3475 (2003); http://dx.doi.org/10.1063/1.1576501 (3 pages) | Cited 16 times

Online Publication Date: 12 May 2003

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The temperature dependence of the first-order magnetic anisotropy constant has been investigated for off-stoichiometric chemically ordered L10, Fe45Pt55 nanoparticle samples. A representative sample shows an anisotropy energy density of Ku = 0.7×107 erg/cm3 and a thermal stability factor of KuV/kBT = 77 at room temperature. With decreasing temperature, from room temperature to 5 K, a 50% increase of Ku, accompanied by a 25% increase of the saturation magnetization MS is observed. The temperature dependence of Ku is explained on the basis of the spin-Hamiltonian approach with an Fe effective spin. The estimated median “magnetic” grain size, obtained from time-dependent measurements, decreases by about 15% with decreasing temperature from 298 to 100 K. This magnetic grain size reduction is attributed to the decrease of the superparamagnetic fraction in the FePt nanoparticle sample. © 2003 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.10.Dg Crystal-field theory and spin Hamiltonians

Magnetic behavior of nanoparticles in patterned thin films

J. Escrig, P. Landeros, J. C. Retamal, D. Altbir, and J. d’Albuquerque e Castro

Appl. Phys. Lett. 82, 3478 (2003); http://dx.doi.org/10.1063/1.1573333 (3 pages) | Cited 9 times

Online Publication Date: 12 May 2003

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The magnetic behavior of truncated conical nanoparticles in patterned thin films is investigated as a function of their size and shape. Using a scaling technique, phase diagrams giving the relative stability of characteristic internal magnetic structures of the particles are obtained. The role of the uniaxial anisotropy in determining the magnetic properties of such systems is discussed, and a simple method for establishing its strength is proposed. © 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
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
61.46.-w Structure of nanoscale materials
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.)

Thermal effect on the field-dependent refractive index of the magnetic fluid film

Y. F. Chen, S. Y. Yang, W. S. Tse, H. E. Horng, Chin-Yih Hong, and H. C. Yang

Appl. Phys. Lett. 82, 3481 (2003); http://dx.doi.org/10.1063/1.1576292 (3 pages) | Cited 13 times

Online Publication Date: 12 May 2003

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The field-dependent refractive index (nMF–H curve) of the magnetic fluid film (MFF) is measured at various temperatures to investigate the thermal effect on the refractive index. It was found, at a certain temperature, that the refractive index becomes higher under higher magnetic fields. This nMF–H curve is moved toward the region with lower nMF when the temperature is raised. Since the variation in the refractive index of the MF under external fields is due to the formation of the magnetic columns, the structural patterns are then examined to clarify the origin of the change in the nMF–H curve with the temperature. Under a given field strength, the particles of columns are dispersed into the liquid carrier at a higher temperature. This depresses the phase separation in the MFF under fields, and in turn, reduces the refractive index of the MFF. The observed results also reveal that the temperature exhibits a compensation effect on the refractive index of the MFF with respect to the magnetic field. © 2003 American Institute of Physics.
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78.66.Nk Insulators
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
75.50.Mm Magnetic liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.15.+e Liquid thin films
64.75.-g Phase equilibria

Hybridization reduction of the magnetization for N-doped FeCo superlattices

Miyoung Kim and A. J. Freeman

Appl. Phys. Lett. 82, 3484 (2003); http://dx.doi.org/10.1063/1.1576917 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2003

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In search of a soft magnetic material exhibiting high magnetization, we investigated the magnetic and structural properties of an (Fe3Co)4Nm superlattice (SL) with (m = 2) and without (m = 0) N doping via first principles full-potential linearized augmented plane wave calculations in order to examine the possible magnetic enhancement by (i) N addition (which has drawn considerable attention since the first report (in 1972) of a giant magnetic moment for quasistable α″-Fe16N2) and (ii) the lowered dimensionality of the SL. The structural optimization was fully accomplished by total energy and atomic force calculations within the generalized-gradient approximation. Despite the lattice expansion by 9% due to the N insertion, the magnetization of (Fe3Co)4N2 was found to be reduced from the value of the Fe3Co superlattice by the strong hybridization of N with Fe and Co. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Monolithic low-transition-temperature superconducting magnetometers for high resolution imaging magnetic fields of room temperature samples

F. Baudenbacher, L. E. Fong, J. R. Holzer, and M. Radparvar

Appl. Phys. Lett. 82, 3487 (2003); http://dx.doi.org/10.1063/1.1572968 (3 pages) | Cited 12 times

Online Publication Date: 12 May 2003

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We have developed a monolithic low-temperature superconducting quantum interference device (SQUID) magnetometer and incorporated the device in a scanning microscope for imaging magnetic fields of room temperature samples. The instrument has a ∼ 100 μm spatial resolution and a 1.4 pT/Hz1/2 field sensitivity above a few hertz. We discuss design constraints on and potential applications of the SQUID microscope. © 2003 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Laser ablation of Co:ZnO films deposited from Zn and Co metal targets on (0001) Al2O3 substrates

W. Prellier, A. Fouchet, B. Mercey, Ch. Simon, and B. Raveau

Appl. Phys. Lett. 82, 3490 (2003); http://dx.doi.org/10.1063/1.1578183 (3 pages) | Cited 82 times

Online Publication Date: 12 May 2003

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We report on the synthesis of high-quality Co-doped ZnO thin films using the pulsed laser deposition technique on (0001)-Al2O3 substrates performed in an oxidizing atmosphere, using Zn and Co metallic targets. We first optimized the growth of ZnO in order to obtain the less strained film. Highly crystallized Co:ZnO thin films are obtained by an alternative deposition from Zn and Co metal targets. This procedure allows an homogenous repartition of the Co in the ZnO wurzite structure which is confirmed by the linear dependence of the out-of-plane lattice parameter as a function of the Co dopant. In the case of 5% Co doped, the film exhibits ferromagnetism with a Curie temperature close to the room temperature. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
68.55.-a Thin film structure and morphology
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition
75.70.Ak Magnetic properties of monolayers and thin films
68.60.Bs Mechanical and acoustical properties
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