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30 Jan 2006

Volume 88, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 88, 051101 (2006); http://dx.doi.org/10.1063/1.2168491 (3 pages)

H. Lohmeyer, K. Sebald, C. Kruse, R. Kröger, J. Gutowski, D. Hommel, J. Wiersig, N. Baer, and F. Jahnke
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Cycle-by-cycle observation of single-domain-to-vortex transitions in magnetic nanodisks

Ana-Vanessa Jausovec, Gang Xiong, and Russell P. Cowburn

Appl. Phys. Lett. 88, 052501 (2006); http://dx.doi.org/10.1063/1.2170403 (3 pages) | Cited 10 times

Online Publication Date: 30 January 2006

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The switching behavior of permalloy (Ni81Fe19) disks with dimensions close to the experimentally determined phase boundary separating the single domain and vortex ground states was investigated. The disks fabricated with electron beam lithography and thermal evaporation were 97 nm wide and 26 nm thick. The remanence curve, measured with a magneto-optical Kerr magnetometer, shows the presence of three different remanence states in different magnetic field regimes; vortex state at fields below 110 Oe, metastable state at fields 110 Oe<H<520 Oe, and single domain state at fields above 520 Oe. High sensitivity magneto-optical measurements combined with an advanced applied field sequence allowed a cycle-by-cycle observation of the collapse of the single domain state into the vortex ground state via a partially remanent metastable state.
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75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Superconductor-semiconductor magnetic microswitch

C. Castellana, F. Giazotto, M. Governale, F. Taddei, and F. Beltram

Appl. Phys. Lett. 88, 052502 (2006); http://dx.doi.org/10.1063/1.2172018 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2006

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A hybrid superconductor-two-dimensional electron gas microdevice is presented. Its working principle is based on the suppression of Andreev reflection at the superconductor-semiconductor interface caused by a magnetic barrier generated by a ferromagnetic strip placed on top of the structure. Device switching is predicted with fields up to some mT and working frequencies of several GHz, making it promising for applications ranging from microswitches and storage cells to magnetic field discriminators.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
73.20.−r
73.23.−b
73.40.−c

Fabrication and microstructure of high coercivity FePt thin films at 400 °C

Z. L. Zhao, J. S. Chen, J. Ding, J. B. Yi, B. H. Liu, and J. P. Wang

Appl. Phys. Lett. 88, 052503 (2006); http://dx.doi.org/10.1063/1.2168256 (3 pages) | Cited 21 times

Online Publication Date: 1 February 2006

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L10 phase FePt thin films deposited on MgO (100) single-crystal substrate with good (001) texture were investigated. Epitaxial growth of the FePt (001) films was observed with a deposition temperature of 400 °C. With ultrathin Ag intermediate layers deposited between FePt layers, the film structures changed from an interconnection network to an isolated-island character. The perpendicular coercivity of the FePt film dramatically increased from 6.5 to 32.5 kOe. The improvement of the magnetic properties may be attributed to the formation of island structures by the additive Ag in the FePt films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology

Nonbolometric photoresponse in (La,Pr)0.67Ca0.33MnO3 thin films

Rajeswari M. Kolagani, M. A. Overby, V. N. Smolyaninova, A. Davidson, and D. E. Cox

Appl. Phys. Lett. 88, 052504 (2006); http://dx.doi.org/10.1063/1.2168687 (3 pages) | Cited 1 time

Online Publication Date: 1 February 2006

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We have studied light-induced resistance changes (photoresponse) in the colossal magnetoresistive manganite material (La,Pr)0.67Ca0.33MnO3. The metal-insulator transition in this material is understood to be driven by the percolation of the metallic channel in an inhomogeneous matrix of insulating and metallic components. Our experiments reveal a nonthermal (nonbolometric) component of the light-induced resistance change, in addition to the expected resistance change related to heating (bolometric effect). This nonthermal component is seen only in the metal-insulator transition region. Our results suggest that this component may be associated with the light-induced resistance decrease in the insulating regions through an electronic mechanism.
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75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
64.60.A- Specific approaches applied to studies of phase transitions

Micromagnetic properties of MnAs(0001)/GaAs(111) epitaxial films

R. Engel-Herbert, T. Hesjedal, D. M. Schaadt, L. Däweritz, and K. H. Ploog

Appl. Phys. Lett. 88, 052505 (2006); http://dx.doi.org/10.1063/1.2171790 (3 pages) | Cited 6 times

Online Publication Date: 2 February 2006

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The micromagnetic properties of MnAs thin films grown on the (111)B-oriented GaAs surface have been investigated. Compared to films grown on (001) surfaces, these films exhibit completely different domain patterns, as the c axis of the hexagonal unit cell is oriented normal to the surface. In the course of the first order phase transition, ferromagnetic α-MnAs forms a network of quasihexagonal areas separated by β-MnAs. We present an analysis of the micromagnetic properties based on imaging and simulations. We observe closure domains that either appear as a vortex-like state or a stripe structure.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.50.Dd Nonmetallic ferromagnetic materials

Magnetic field dependence of voltage-current characteristics of Fe3O4 thin films at room temperature

Kun Zhao, Jiafeng Feng, Yanhong Huang, Jian-gao Zhao, Huibin Lu, Xiufeng Han, and Wenshan Zhan

Appl. Phys. Lett. 88, 052506 (2006); http://dx.doi.org/10.1063/1.2171791 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2006

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Fe3O4 thin films have been fabricated on glass substrate by the facing-target sputtering technique and their field-modulated voltage-current behavior was investigated. The nonlinear dependence of voltage on current density displays a switching from high-resistivity to low-resistivity states above a threshold current density. The low-resistivity state is very sensitive to the applied magnetic field, and a large negative magnetoresistance of ∼ −27% is observed at 300 Oe under a high current density of 100 A cm−2 at room temperature. Furthermore, the dependence of the magnetoresistance on the magnetic field reveals a good linear relationship. The observed results seem to favor a picture of spin-polarized intergrain tunneling through the grain boundaries.
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75.70.Ak Magnetic properties of monolayers and thin films
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport

Observation of thermally activated domain wall transformations

M. Laufenberg, D. Backes, W. Bührer, D. Bedau, M. Kläui, U. Rüdiger, C. A. F. Vaz, J. A. C. Bland, L. J. Heyderman, F. Nolting, S. Cherifi, A. Locatelli, R. Belkhou, S. Heun, and E. Bauer

Appl. Phys. Lett. 88, 052507 (2006); http://dx.doi.org/10.1063/1.2168677 (3 pages) | Cited 54 times

Online Publication Date: 2 February 2006

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The spin structure of head-to-head domain walls in Ni80Fe20 structures is studied using high-resolution photoemission electron microscopy. The quantitative phase diagram is extracted from these measurements and found to exhibit two phase boundaries between vortex and transverse domain walls. The results are compared with available theoretical predictions and micromagnetic simulations and differences to the experiment are explained, taking into account thermal excitations. Temperature-dependent measurements show a thermally activated transformation of transverse to vortex domain walls in 7 nm thick and 730 nm wide structures at a transition temperature between 260 °C and 310 °C, which corresponds to a nucleation barrier height for a vortex wall between 6.7×10−21 J and 8.0×10−21 J.
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75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Fe implanted ferromagnetic ZnO

K. Potzger, Shengqiang Zhou, H. Reuther, A. Mücklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdörfer, and T. P. Papageorgiou

Appl. Phys. Lett. 88, 052508 (2006); http://dx.doi.org/10.1063/1.2169912 (3 pages) | Cited 61 times

Online Publication Date: 2 February 2006

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Room-temperature ferromagnetism has been induced within ZnO single crystals by implant doping with Fe ions. For an implantation temperature of 623 K and an ion fluence of 4×1016 cm−2, very tiny Fe particles, formed inside the host matrix, are responsible for the ferromagnetic properties. They were identified using synchrotron x-ray diffraction and Mössbauer spectroscopy. On the other hand, Fe ions implanted at a temperature of 253 K and an ion fluence of 4×1015 cm−2 are incorporated into the host matrix and develop a room temperature diluted magnetic semiconductor.
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75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
75.50.Bb Fe and its alloys
61.72.S- Impurities in crystals
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Enhanced spin injection polarization in Co/Cu/Co nonlocal lateral spin valves

Y. Ji, A. Hoffmann, J. E. Pearson, and S. D. Bader

Appl. Phys. Lett. 88, 052509 (2006); http://dx.doi.org/10.1063/1.2170138 (3 pages) | Cited 30 times

Online Publication Date: 2 February 2006

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Nonlocal spin injection is demonstrated in Co/Cu/Co lateral spin valves. Measurement of a series of structures with varying Cu length between the Co electrodes permits a direct determination of both the Cu spin diffusion length λs and the spin injection polarization P at the Co/Cu interface. The value of λs is 200±20 nm at 10 K and ≥ 110 nm at 300 K, which is shorter than previously reported, due to the possible presence of impurities in the Cu. However, the value of P is >7%, which is improved compared with previous reports of 2%, which is attributed to a higher interfacial quality.
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72.25.Ba Spin polarized transport in metals
75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Hx Magnetic impurity interactions
75.50.Cc Other ferromagnetic metals and alloys
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