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7 Jun 2004

Volume 84, Issue 23, pp. 4599-4816

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4650 (2004); http://dx.doi.org/10.1063/1.1759390 (3 pages)

David I. Woodward, Ian M. Reaney, Gaiying Y. Yang, Elizabeth C. Dickey, and Clive A. Randall
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Magnetization dependence on strain in the Ni–Mn–Ga magnetic shape memory material

I. Suorsa, E. Pagounis, and K. Ullakko

Appl. Phys. Lett. 84, 4658 (2004); http://dx.doi.org/10.1063/1.1759771 (3 pages) | Cited 12 times

Online Publication Date: 19 May 2004

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Magnetic shape memory (MSM) materials can generate up to 10% strain when exposed to a magnetic field. The magnetization of the MSM material is closely related to its strain level. Modeling this relationship is of prime importance, especially in sensor and motion generation applications. In the present work, the magnetization curve of a Ni2MnGa MSM material was measured at different strain levels. The measurements were performed at magnetic fields of up to 130 kA/m, which includes the range used in most sensor applications. The measurement setup is described, and the results are compared with two models of magnetization dependence on strain, a linear and a nonlinear model. It is demonstrated that at high magnetic field strength values the relationship is linear, while at low fields (H<40 kA/m) the dependence between the strain and the magnetization is nonlinear. © 2004 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Dipolar interaction effects on the thermally activated magnetic relaxation of two-dimensional nanoparticle ensembles

S. I. Denisov, T. V. Lyutyy, and K. N. Trohidou

Appl. Phys. Lett. 84, 4672 (2004); http://dx.doi.org/10.1063/1.1759782 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2004

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The thermally activated magnetic relaxation in two-dimensional lattices of dipolar interacting nanoparticles with large uniaxial perpendicular anisotropy is studied by a numerical method and within the mean-field approximation for comparison. The role that the correlation effects play in magnetic relaxation and the influence of lattice structure and bias magnetic field on the relaxation process are revealed. The correlations of the nanoparticle magnetic moments enhance relaxation on small times, delay it on large times, and reduce the steady-state absolute magnetization at nonzero bias fields. In a hexagonal lattice, magnetic relaxation on small times occurs faster and the steady-state absolute magnetization has the larger magnitude than in a square lattice with the same lattice spacing. © 2004 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys

Planar Hall effect sensor for magnetic micro- and nanobead detection

L. Ejsing, M. F. Hansen, A. K. Menon, H. A. Ferreira, D. L. Graham, and P. P. Freitas

Appl. Phys. Lett. 84, 4729 (2004); http://dx.doi.org/10.1063/1.1759380 (3 pages) | Cited 59 times

Online Publication Date: 20 May 2004

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Magnetic bead sensors based on the planar Hall effect in thin films of exchange-biased permalloy have been fabricated and characterized. Typical sensitivities are 3 μV/Oe mA. The sensor response to an applied magnetic field has been measured without and with coatings of commercially available 2 μm and 250 nm magnetic beads used for bioapplications (Micromer-M and Nanomag-D, Micromod, Germany). Detection of both types of beads and single bead detection of 2 μm beads is demonstrated, i.e., the technique is feasible for magnetic biosensors. Single 2 μm beads yield 300 nV signals at 10 mA and 15 Oe applied field. © 2004 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
85.75.Nn Hybrid Hall devices

La0.7Pr0.3MnO3 ceramic: An electron-doped colossal magnetoresistive manganite

Ping Duan, Zhenghao Chen, Shouyu Dai, Yueliang Zhou, Huibin Lu, Kuijuan Jin, and Bolin Cheng

Appl. Phys. Lett. 84, 4741 (2004); http://dx.doi.org/10.1063/1.1759775 (3 pages) | Cited 8 times

Online Publication Date: 20 May 2004

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We report a study on the synthesis, electrical transport, and magnetic properties of Pr-doped LaMnO3 ceramic material. We have found that La1−xPrxMnO3+δ (x = 0.3) synthesized using solid-state reaction shows semiconductor behavior, and no colossal magnetoresistance (CMR) effect; while it shows CMR behavior when it is annealed in a flowing argon at certain temperature (about 873 K), which suggests that La0.7Pr0.3MnO3+δ has been transferred to La0.7Pr0.3MnO3. The x-ray photoemission spectroscopy reveals that Pr ions are in a mixed-valence state of Pr4+ and Pr3+ in this compound. Therefore, La1−xPrxMnO3 (x = 0.3) could be an electron-doped CMR manganite. © 2004 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
72.60.+g Mixed conductivity and conductivity transitions

Gd5Si2Ge2 composite for magnetostrictive actuator applications

Nersesse Nersessian, Siu Wing Or, Gregory P. Carman, Scott K. McCall, Wonyoung Choe, Harry B. Radousky, Mike W. McElfresh, Vitalij K. Pecharsky, and Alexandra O. Pecharsky

Appl. Phys. Lett. 84, 4801 (2004); http://dx.doi.org/10.1063/1.1760891 (3 pages) | Cited 9 times

Online Publication Date: 21 May 2004

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A composite system containing particles of Gd5Si2Ge2, which exhibit a colossal magnetic-field-induced strain, has been prepared. The composite is manufactured by embedding ball-milled Gd5Si2Ge2 particles with a size distribution of <600 μm in a resin matrix. The thermally induced volume strain in the composite resulting from phase transformation is found to be 1300 ppm. The magnetically induced linear strain resulting from phase transformation is also measured, from which the volume strain is deduced to be 1650 ppm. The volume strain from the composite is significantly lower than phase transformation strain of the bulk Gd5Si2Ge2 (8000 ppm) and is mainly attributed to nonalignment of the particles in the matrix. An analytical model for a 1–3 composite (particles aligned in a single direction in a polymer matrix) and a 0–3 composite (particles dispersed randomly in a polymer matrix) predicts significantly higher strains in a 1–3 composite. © 2004 American Institute of Physics.
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81.20.Wk Machining, milling
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Qk Reinforced polymers and polymer-based composites
75.80.+q Magnetomechanical effects, magnetostriction
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Strong magnetic-field effects in weak manganite-based heterojunction

J. R. Sun, C. M. Li, and H. K. Wong

Appl. Phys. Lett. 84, 4804 (2004); http://dx.doi.org/10.1063/1.1762703 (3 pages) | Cited 22 times

Online Publication Date: 21 May 2004

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Oxide heterojunctions were fabricated by growing a La0.67Ca0.33MnO3−δ (LCMO) film on a 0.5 wt % Nb-doped SrTiO3 single crystal (STON). By removing the oxygen of LCMO, a junction with a rather small diffusion/breakdown voltage and junction resistance has been obtained. The most striking observation of the present work is the extremely strong magnetic-field effects in this weak junction. A field of H ≈ 1.7 T can cause an increase of ∼1130% of the diffusion/breakdown voltage and a magnetoresistance as high as R(H)/R(0)−1 ≈ 1100%. It is interesting to note that the magnetoresistance is positive, which indicates a basically different mechanism from the manganite, for which a negative magnetoresistance is observed, and could be a result of the change of magnetic and electronic structures of LCMO with respect to STON under magnetic field. © 2004 American Institute of Physics.
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73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.61.Le Other inorganic semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Lx Magnetic oxides
75.50.Pp Magnetic semiconductors
81.15.Fg Pulsed laser ablation deposition
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
71.20.Ps Other inorganic compounds
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