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12 Nov 2007

Volume 91, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 91, 203501 (2007); http://dx.doi.org/10.1063/1.2806922 (3 pages)

Michael N. Feiginov and Dibakar Roy Chowdhury
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Temperature induced single domain–vortex state transition in sub-100 nm Fe nanodots

Randy K. Dumas, Kai Liu, Chang-Peng Li, Igor V. Roshchin, and Ivan K. Schuller

Appl. Phys. Lett. 91, 202501 (2007); http://dx.doi.org/10.1063/1.2807276 (3 pages) | Cited 16 times

Online Publication Date: 12 November 2007

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Magnetization reversal in nanomagnets via a vortex state, although often investigated at the remanent state, may not necessarily display a zero remanence or a highly pinched hysteresis loop. In contrast, the irreversible nucleation/annihilation events are clear indications of a vortex state. In this work, temperature induced single domain–vortex state transition has been investigated in 67 nm Fe nanodots using a first-order reversal curve (FORC) technique. The two phase coexistence is manifested as different features in the FORC distribution. At lower temperatures, it becomes harder to nucleate and annihilate vortices and the amount of single domain dots increases.
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75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Pumping spin states of molecular magnets by strong rotating magnetic field

A. Hernández-Mínguez, C. Carbonell-Cortés, R. Amigó, J. M. Hernandez, J. Tejada, and E. M. Chudnovsky

Appl. Phys. Lett. 91, 202502 (2007); http://dx.doi.org/10.1063/1.2803766 (3 pages) | Cited 2 times

Online Publication Date: 13 November 2007

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We report experiments on magnetic avalanches in a Mn12-acetate crystal at a frequency up to 50 avalanches/s, produced by a rotating magnetic field up to 1 T. This method permits maintaining an elevated population of excited spin levels. It can be used for the studies of spin-phonon interactions and for a deeper understanding of the phonon bottleneck problem.
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75.50.Xx Molecular magnets
63.20.-e Phonons in crystal lattices
75.60.Jk Magnetization reversal mechanisms

Memory effect in a system of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs

W. Z. Wang, J. J. Deng, J. Lu, B. Q. Sun, and J. H. Zhao

Appl. Phys. Lett. 91, 202503 (2007); http://dx.doi.org/10.1063/1.2814037 (3 pages) | Cited 6 times

Online Publication Date: 14 November 2007

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Zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs matrices are fabricated by in situ postgrowth annealing diluted magnetic semiconductor (Ga,Mn)As films with Mn concentration ranging from 2.6% to 8% at 650 °C. Magnetization measurements show that memory effect and slow magnetic relaxation, the typical characteristics of the spin-glass-like phase, occur below the blocking temperature of 45 K in samples with high Mn concentration, while for samples with low Mn concentration, ferromagnetic order remains up to 360 K. The behavior of low-temperature spin dynamics can be explained by the hierarchical model.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
75.50.Lk Spin glasses and other random magnets
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials

Epitaxial thin films of multiferroic GaFeO3 on conducting indium tin oxide (001) buffered yttrium-stabilized zirconia (001) by pulsed laser deposition

M. Trassin, N. Viart, G. Versini, J.-L. Loison, J.-P. Vola, G. Schmerber, O. Crégut, S. Barre, G. Pourroy, J. H. Lee, W. Jo, and C. Mény

Appl. Phys. Lett. 91, 202504 (2007); http://dx.doi.org/10.1063/1.2813020 (3 pages) | Cited 3 times

Online Publication Date: 14 November 2007

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Epitaxial films of an alternative multiferroic material, GaFeO3 (GFO), were grown by pulsed laser deposition on yttrium-stabilized zirconia (001) and on conducting buffer layers of indium tin oxide (001). They present a perfect epitaxial growth along the GFO [010] axis and six crystallographic variants in the film’s plane. Their magnetic properties are close to those of the bulk with an out-of-plane [010] hard direction and a Curie temperature of ∼ 200 K. The films did exhibit ferroelectric properties when characterized by electrostatic force microscopy.
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81.15.Fg Pulsed laser ablation deposition
77.55.-g Dielectric thin films
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.80.Dj Domain structure; hysteresis

Multiferroic properties of polycrystalline Bi1−xCaxFeO3

Deepti Kothari, V. Raghavendra Reddy, Ajay Gupta, Vasant Sathe, A. Banerjee, S. M. Gupta, and A. M. Awasthi

Appl. Phys. Lett. 91, 202505 (2007); http://dx.doi.org/10.1063/1.2806199 (3 pages) | Cited 29 times

Online Publication Date: 14 November 2007

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It is shown that Ca2+ doping at Bi-site results in the release of weak ferromagnetism in BiFeO3. Structural transformation from rhombohedral to triclinic is observed with 10% Ca doping. Raman measurements show the presence of oxygen vacancies with Ca doping and no evidence of either intermediate valence or the tetravalence of iron is observed from Mössbauer measurements. No significant change in Neel temperature is observed with Ca doping. The observed weak ferromagnetism and ferroelectric nature at room temperature indicates the multiferroic nature of Bi1−xCaxFeO3 (x = 5% and 10%) samples.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
77.80.-e Ferroelectricity and antiferroelectricity
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Induced magnetism in Cu nanoparticles embedded in Co

P. Swaminathan, R. A. Rosenberg, G. K. Shenoy, J. S. Palmer, and J. H. Weaver

Appl. Phys. Lett. 91, 202506 (2007); http://dx.doi.org/10.1063/1.2806236 (3 pages) | Cited 1 time

Online Publication Date: 14 November 2007

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One-dimensionally confined nonferromagnetic layers of Cu grown between ferromagnetic layers of Co have an average induced magnetic moment that decreases with Cu film thickness. We studied the effects of changing the nature of confinement to three dimensions by embedding Cu nanoparticles in a Co matrix and measuring the induced moments using x-ray magnetic circular dichroism. The nanoparticle spin moments were more than twice that of films of comparable thickness due to the three dimensional confinement and greater interfacial area.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
78.66.Bz Metals and metallic alloys
78.20.Ls Magneto-optical effects

Using ring-shaped and magnetically coated tungsten wire as the probe of spin-polarized scanning tunneling microscopy

Chii-Bin Wu, Pin-Jui Hsu, Hong-Yu Yen, and Minn-Tsong Lin

Appl. Phys. Lett. 91, 202507 (2007); http://dx.doi.org/10.1063/1.2813614 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2007

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We report a method of magnetic probe fabrication using ring-shaped and iron-coated tungsten wire for spin-polarized scanning tunneling microscopy. Magneto-optic Kerr effect measurement on the probe front end shows that by controlling the saturating field direction, we can fix the probe magnetization in the specific in-plane direction. The ring is applied to the scanning tunneling microscopy and spectroscopy experiment on 6.8 ML Mn/Fe(001), and spin contrast in the in-plane direction is demonstrated.
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72.25.-b Spin polarized transport
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Minute pinning and doping additions for strong, 20 K, in-field critical current improvement in MgB2

P. Mikheenko, S. K. Chen, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 91, 202508 (2007); http://dx.doi.org/10.1063/1.2814060 (3 pages) | Cited 11 times

Online Publication Date: 15 November 2007

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Minute additions of a combination of Dy2O3 and B4C have been used to enhance both pinning and upper critical field in MgB2. A delicate balance of Dy2O3 and B4C additions is required to improve properties. The Dy2O3 nanoparticles react with B to form 10–15 nm DyB4 nanoparticles, while B4C supplies carbon into the MgB2 crystal lattice and increases the upper critical field. The optimum level of Dy2O3 and B4C additions is ∼ 0.5 wt % of Dy2O3 and 0.04 wt % of B4C, yielding a Jc (20 K) of 105 A cm−2 at 2.7 T.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.62.Dh Effects of crystal defects, doping and substitution

Effect of oxygen concentration on the magnetic properties of La2CoMnO6 thin films

H. Z. Guo, A. Gupta, Jiandi Zhang, M. Varela, and S. J. Pennycook

Appl. Phys. Lett. 91, 202509 (2007); http://dx.doi.org/10.1063/1.2814919 (3 pages) | Cited 8 times

Online Publication Date: 16 November 2007

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The dependence of the magnetic properties on oxygen concentration in epitaxial La2CoMnO6 thin films deposited on (100)-oriented SrTiO3 substrates has been investigated by varying the oxygen background pressure during growth using pulsed laser deposition. Two distinct ferromagnetic (FM) phases are revealed, and the relative fraction varies with the oxygen concentration. The existence of oxygen vacancies induces the local vibronic Mn3+–O–Co3+ superexchange interactions in direct competition with the static FM Mn4+–O–Co2+ interactions. This results in the appearance of a new low temperature FM phase and suppression of the high-temperature FM phase, creating two distinct magnetic phase transitions.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition

Superconducting microrings as magnetic pinning centers

W. Gillijns, A. V. Silhanek, and V. V. Moshchalkov

Appl. Phys. Lett. 91, 202510 (2007); http://dx.doi.org/10.1063/1.2815656 (3 pages) | Cited 1 time

Online Publication Date: 16 November 2007

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The nucleation of the superconducting condensate in an Al film deposited on top of a periodic array of microsized Pb rings is investigated using transport measurements. We demonstrate that these Pb rings form tunable pinning sites which can be switched at will to repel or attract vortices in the Al film, depending on their magnetic history. After zero field cooling, a repulsive interaction between the rings and the vortices is observed, while after field cooling, the interaction becomes attractive. The flexibility of such current-induced pinning centers can lead to an enhanced control over the vortex motion.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Op Mixed states, critical fields, and surface sheaths

Direct observation of quantized interlayer vortex flow in a high-Tc La1.87Sr0.13CuO4 single crystal

I. Iguchi, S. Arisawa, K.-S. Yun, T. Hatano, T. Uchiyama, and I. Tanaka

Appl. Phys. Lett. 91, 202511 (2007); http://dx.doi.org/10.1063/1.2815659 (3 pages)

Online Publication Date: 16 November 2007

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We have observed directly the magnetic images of the dynamic motion of quantized interlayer vortices induced by the Lorentz force in an anisotropic high-Tc La1.87Sr0.13CuO4 single crystal. A scanning superconducting quantum interface device microscope is used for this study and it is found that three modes of flux motion exist depending on the transport current. By increasing the sample current‖c axis, a transition from the creeplike behavior to a steady flow of vortices was observed. Even higher current induced a continuous expansion of vortex-flow area depending on the inhomogeneity of the pinning force in a crystal.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
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