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2 May 2011

Volume 98, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 98, 183101 (2011); http://dx.doi.org/10.1063/1.3584006 (3 pages)

Tuba Oznuluer, Ercag Pince, Emre O. Polat, Osman Balci, Omer Salihoglu, and Coskun Kocabas
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First-principles studies on magnetic properties of rocksalt structure MC (M = Ca, Sr, and Ba) under pressure

Shengjie Dong and Hui Zhao

Appl. Phys. Lett. 98, 182501 (2011); http://dx.doi.org/10.1063/1.3586257 (3 pages) | Cited 7 times

Online Publication Date: 3 May 2011

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Magnetic properties of sp-electron half-metallic ferromagnets (HMFs) MC (M = Ca, Sr, and Ba) in rocksalt structure at ambient and elevated pressure have been investigated using first-principles within the generalized gradient approximation in the scheme of Perdew et al. [Phys. Rev. Lett. 77, 3865 (1996)] . Magnetic moments, lattice constants, and total energies are calculated as a function of external pressure. The calculations predict the occurrence of pressure-induced magnetic phase transitions and find that the main reason for the magnetic transitions of sp-electron HMFs is the band widening of anion p states.
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71.15.-m Methods of electronic structure calculations
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
61.66.-f Structure of specific crystalline solids
71.15.Nc Total energy and cohesive energy calculations
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

How the size distribution of magnetic nanoparticles determines their magnetic particle imaging performance

D. Eberbeck, F. Wiekhorst, S. Wagner, and L. Trahms

Appl. Phys. Lett. 98, 182502 (2011); http://dx.doi.org/10.1063/1.3586776 (3 pages) | Cited 4 times

Online Publication Date: 4 May 2011

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Spatial and temporal resolution of magnetic particle imaging (MPI), a powerful technique for biomedical imaging, depends crucially on the magnetic properties of the magnetic nanoparticle (MNP) tracer. The authors establish the relation of the static and the dynamic magnetization behavior of various MNP preparations to their MPI performance. While MNPs with a mean diameter of 6 nm achieve only 0.2% of the theoretical maximum amplitude of the third harmonic (at 25 kA/m drive field strength), those with 19 nm diameter attain 57%. The good performance of Resovist, a clinically approved contrast agent for magnetic resonance imaging, is explained by the presence of MNP aggregates.
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87.85.Rs Nanotechnologies-applications
87.61.-c Magnetic resonance imaging
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Injection locking of tunnel junction oscillators to a microwave current

M. Quinsat, J. F. Sierra, I. Firastrau, V. Tiberkevich, A. Slavin, D. Gusakova, L. D. Buda-Prejbeanu, M. Zarudniev, J.-P. Michel, U. Ebels, B. Dieny, M.-C. Cyrille, J. A. Katine, D. Mauri, and A. Zeltser

Appl. Phys. Lett. 98, 182503 (2011); http://dx.doi.org/10.1063/1.3587575 (3 pages) | Cited 3 times

Online Publication Date: 5 May 2011

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Injection locking of a spin transfer nano-oscillator, based on an in-plane magnetized magnetic tunnel junction and generating the frequency f0, to an external signal of varying frequency fe is studied experimentally and with macrospin simulations. It is shown, that if the driving signal has the form of a microwave current, the locking effect is well-pronounced near fe ≅ 2f0, but is almost completely absent near fe ≅ f0, confirming predictions of analytical theory. It is also shown that noise plays an important role in the locking process, causing the linewidth of the locked oscillation to substantially exceed that of the driving signal.
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84.30.Ng Oscillators, pulse generators, and function generators

Time-resolved resonant soft x-ray diffraction with free-electron lasers: Femtosecond dynamics across the Verwey transition in magnetite

N. Pontius, T. Kachel, C. Schüßler-Langeheine, W. F. Schlotter, M. Beye, F. Sorgenfrei, C. F. Chang, A. Föhlisch, W. Wurth, P. Metcalf, I. Leonov, A. Yaresko, N. Stojanovic, M. Berglund, N. Guerassimova, et al.

Appl. Phys. Lett. 98, 182504 (2011); http://dx.doi.org/10.1063/1.3584855 (3 pages) | Cited 3 times

Online Publication Date: 5 May 2011

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Resonant soft x-ray diffraction (RSXD) with femtosecond (fs) time resolution is a powerful tool for disentangling the interplay between different degrees of freedom in strongly correlated electron materials. It allows addressing the coupling of particular degrees of freedom upon an external selective perturbation, e.g., by an optical or infrared laser pulse. Here, we report a time-resolved RSXD experiment from the prototypical correlated electron material magnetite using soft x-ray pulses from the free-electron laser FLASH in Hamburg. We observe ultrafast melting of the charge-orbital order leading to the formation of a transient phase, which has not been observed in equilibrium.
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78.47.D- Time resolved spectroscopy (>1 psec)
71.30.+h Metal-insulator transitions and other electronic transitions
41.60.Cr Free-electron lasers

Giant magnetic flux jumps in single crystals of Ba0.6K0.4Fe2As2

Ki-Young Choi, Gun Sang Jeon, X. F. Wang, X. H. Chen, Xiao-Lin Wang, Myung-Hwa Jung, Sung-Ik Lee, and Gangseo Park

Appl. Phys. Lett. 98, 182505 (2011); http://dx.doi.org/10.1063/1.3586777 (3 pages)

Online Publication Date: 5 May 2011

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Giant magnetic flux jumps are observed in magnetic hysteresis loops of Ba0.6K0.4Fe2As2 single crystals. The size of the flux jumps, which appear only at low temperatures (T<4 K), is so large that it can transform the whole superconducting state into the normal state. The recovery rate to the superconducting state is rather slow, although the superconducting state is almost fully recovered. We show that theoretical predictions based on the adiabatic approach with nonlocal electrodynamics give a good explanation of the flux jumps observed in the single crystals of Ba0.6K0.4Fe2As2.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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