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10 Feb 2003

Volume 82, Issue 6, pp. 841-996

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 913 (2003); http://dx.doi.org/10.1063/1.1542686 (3 pages)

F. Gao and W. J. Weber
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Surface-induced phase separation in manganites: A microscopic origin for powder magnetoresistance

M. Bibes, Ll. Balcells, J. Fontcuberta, M. Wojcik, S. Nadolski, and E. Jedryka

Appl. Phys. Lett. 82, 928 (2003); http://dx.doi.org/10.1063/1.1543235 (3 pages) | Cited 32 times

Online Publication Date: 4 February 2003

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Through the analysis of the magnetic properties and of the nuclear magnetic resonance response of La2/3Ca1/3MnO3 ceramics with different grain sizes, we have found that poorly conducting regions, some ferromagnetic and some weakly magnetic, are located at the surface of the grains. We state that these regions constitute the tunnel barrier responsible for the low-field magnetoresistance usually observed in powders of half-metallic oxides. In addition, the spin disorder accompanying the coexistence of phases with different magnetoelectronic character could contribute to the large high-field magnetoresistance also typical of such ceramic samples. From a more general perspective, these findings can be of relevance to understand the microscopic origin of phase separation in manganites. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
75.70.Rf Surface magnetism
75.50.Tt Fine-particle systems; nanocrystalline materials
76.60.-k Nuclear magnetic resonance and relaxation
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Cc Other ferromagnetic metals and alloys

Noise sources and dissipation mechanisms of a 120 ℏ SQUID amplifier

Paolo Falferi, Michele Bonaldi, Antonella Cavalleri, Massimo Cerdonio, Andrea Vinante, Renato Mezzena, Ke-xi Xu, Giovanni Andrea Prodi, and Stefano Vitale

Appl. Phys. Lett. 82, 931 (2003); http://dx.doi.org/10.1063/1.1542673 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2003

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A two-stage superconducting quantum interference device (SQUID), based on a commercial sensor, is strongly coupled to an electrical resonator at 11 kHz with a quality factor Q = 600 000 and operated in the temperature range 1.33–4.17 K. From the analysis of the noise generated by this system, the back action noise of the SQUID amplifier is estimated. The minimum noise temperature, calculated from back action and additive noise measurements, is 63 μK at 1.33 K, and corresponds to 120 times the quantum-limited noise temperature. We discuss and experimentally verify a mechanism, which can limit the noise temperature and add losses to the system. © 2003 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.30.Le Amplifiers
07.50.Hp Electrical noise and shielding equipment

Enhancement of room-temperature magnetoresistance in Sr2FeMoO6 by reducing its grain size and adjusting its tunnel-barrier thickness

C. L. Yuan, Y. Zhu, and P. P. Ong

Appl. Phys. Lett. 82, 934 (2003); http://dx.doi.org/10.1063/1.1544066 (3 pages) | Cited 14 times

Online Publication Date: 4 February 2003

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The intergrain magnetoresistance (IMR) of polycrystalline Sr2FeMoO6 is known to depend on its grain size and the tunnel barrier thickness formed during fabrication. Further enhancement of the IMR of Sr2FeMoO6 is found possible by further decreasing its grain size using high-energy ball milling, as well as by judiciously adjusting the tunnel barrier thickness. The tunnel barrier thickness depends on the amount of insulating nonmagnetic SrMoO4 impurity formed during fabrication, which in turn can be controlled by varying the mixture ratio of the ambient gaseous H2–Ar stream during annealing. With smaller grain size, the magnetic domain size decreases correspondingly and so can be more easily rotated to produce a lower coercive field. The increase in the SrMoO4 impurity phase increases the number of grain boundary barriers in the Sr2FeMoO6 matrix, leading to a larger low-field magnetoresistance effect (LFMR). A significant enhancement of the LFMR was found when the SrMoO4 impurity was close to the conduction threshold. Compared to the artificial fabrication of multilayer structures, our method is much simpler and offers an enhanced technology to fabricate suitable tunneling barriers in magnetoresistive devices. © 2003 American Institute of Physics.
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75.47.Pq Other materials
61.72.Cc Kinetics of defect formation and annealing
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Induced magnetic anisotropy in amorphous ribbons by applying a magnetic field during the quenching process

M. Tejedor, J. A. García, J. Carrizo, L. Elbaile, and J. D. Santos

Appl. Phys. Lett. 82, 937 (2003); http://dx.doi.org/10.1063/1.1542675 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2003

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A method to induce magnetic anisotropy in amorphous magnetic ribbons has been developed. The anisotropy is induced in the high Curie temperature Fe80B20 and Co70Mn5Fe1Mo1Si14B9 amorphous magnetic ribbons by applying a magnetic field at the moment of the solidification of the melt. This method does not affect the excellent mechanical properties of these materials. The induced magnetic anisotropy has been measured by torque magnetometry and its strength and easy axis are compared with the results obtained by other authors using static magnetic annealing in similar samples. © 2003 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.30.Fb Solidification
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Open-type hybrid magnetic shield using high-TC superconducting wire and flexible magnetic sheets

Yusuke Seki, Daisuke Suzuki, Kuniomi Ogata, and Keiji Tsukada

Appl. Phys. Lett. 82, 940 (2003); http://dx.doi.org/10.1063/1.1544064 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2003

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An open-ended, cylindrical magnetic shield using high-TC superconducting rings and flexible magnetic sheets has been developed. The superconducting ring is made of Bi2Sr2Ca2Cu3Ox tape wire, and the flexible magnetic sheet is made of Fe–Cu–Nb–Si–B nanocrystalline alloy, which has superior soft magnetic properties. The superconducting rings are set near the open ends of a ferromagnetic cylinder. When a magnetic field is induced in the rings, a shielding current flows so as to keep the magnetic flux through the ring constant. It is concluded that the superconducting rings effectively increase the shielding factor of a magnetic shield. © 2003 American Institute of Physics.
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07.55.Nk Magnetic shielding in instruments
84.71.Mn Superconducting wires, fibers, and tapes

Pinning characteristics in chemically modified (Nd, Eu, Gd)–Ba–Cu–O superconductors

M. Muralidhar, N. Sakai, M. Nishiyama, M. Jirsa, T. Machi, and M. Murakami

Appl. Phys. Lett. 82, 943 (2003); http://dx.doi.org/10.1063/1.1542927 (3 pages) | Cited 22 times

Online Publication Date: 4 February 2003

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In melt-processed (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy (NEG-123) materials we found a new type of nanometer-scale pinning defects. Structural analysis was made with a dynamic force microscope and a scanning tunneling microscope (STM) that both showed the formation of a nanometer-scale lamellar structure. The high magnification STM showed that the nanolamellas are in fact rows (or planes) of aligned NEG-rich clusters 3–4 nm in size. This new pinning medium led to an increase of Birr at 77 K for the H∥ c axis up to 12 T (measured by a superconducting quantum interference device) or 15 T (measured by a vibrating sample magnetometer). A secondary peak as high as 70 kA/cm2 was observed at 4.5 T and decreased to 49 and 22 kA/cm2 at 7 and 10 T, respectively. © 2003 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.66.Bi Elemental solids
61.66.Dk Alloys
74.25.Ha Magnetic properties including vortex structures and related phenomena

FeCo–Zr–O nanogranular soft-magnetic thin films with a high magnetic flux density

S. Ohnuma, H. Fujimori, T. Masumoto, X. Y. Xiong, D. H. Ping, and K. Hono

Appl. Phys. Lett. 82, 946 (2003); http://dx.doi.org/10.1063/1.1537456 (3 pages) | Cited 24 times

Online Publication Date: 4 February 2003

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Soft-magnetic thin films with high magnetic flux densities of about 23 kG have been fabricated in the (Fe–Co)–Zr–O nanogranular system. The films were prepared by reactive sputtering under an oxygen–argon atmosphere using a target of Fe–Co–Zr alloys. The microstructure was composed of base-centered-cubic Fe–Co nanograins, where nanoparticles of amorphous Zr oxide are dispersed. These Zr-oxide nanoparticles are thought to hinder the growth of Fe–Co grains during the film deposition, causing low coercivity. © 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.Bc Nanocrystalline materials
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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