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24 Aug 2009

Volume 95, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 95, 082507 (2009); http://dx.doi.org/10.1063/1.3186782 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, and Dong-Soo Han
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Effects of particle dipole interaction on the ac magnetically induced heating characteristics of ferrite nanoparticles for hyperthermia

Minhong Jeun, Seongtae Bae, Asahi Tomitaka, Yasushi Takemura, Ki Ho Park, Sun Ha Paek, and Kyung-Won Chung

Appl. Phys. Lett. 95, 082501 (2009); http://dx.doi.org/10.1063/1.3211120 (3 pages) | Cited 18 times

Online Publication Date: 24 August 2009

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Magnetic particle dipole interaction was revealed as a crucial physical parameter to be considered in optimizing the ac magnetically induced heating characteristics of magnetic nanoparticles. The ac heating temperature of soft MFe2O4 (M = Mg,Ni) nanoparticles was remarkably increased from 17.6 to 94.7 °C (MgFe2O4) and from 13.1 to 103.1 °C (NiFe2O4) by increasing the particle dipole interaction energy at fixed ac magnetic field of 140 Oe and frequency of 110 kHz. The increase in “magnetic hysteresis loss” that resulted from the particle dipole interaction was the main physical reason for the significant improvement of ac heating characteristics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
87.19.Pp Biothermics and thermal processes in biology
75.50.Gg Ferrimagnetics

Magnetization relaxation and structure of CoFeGe alloys

H. Lee, Y.-H. A. Wang, C. K. A. Mewes, W. H. Butler, T. Mewes, S. Maat, B. York, M. J. Carey, and J. R. Childress

Appl. Phys. Lett. 95, 082502 (2009); http://dx.doi.org/10.1063/1.3207749 (3 pages) | Cited 12 times

Online Publication Date: 24 August 2009

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The magnetic relaxation of 10 and 50 nm thin films of (CoFe)100−xGex (0 at. % ≤ x ≤ 35 at. %) alloys was investigated by broadband ferromagnetic resonance (FMR) experiments. 10 nm thin films exhibit a significant two magnon contribution to the FMR linewidth. The 50 nm films exhibit very low damping constants of α ≈ 0.0025 and relaxation rates as low as 33 MHz in the composition range of 20 at. % ≤ x ≤ 30 at. % Ge after annealing. Structural characterization revealed B2 order for these compositions. First principles calculations confirm a pseudogap in the minority channel for B2 ordered (CoFe)75Ge25 which may cause the low damping parameters and high ΔRA in CoFeGe based current perpendicular to the plane giant magnetoresistance spin valves.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.40.Gh Other heat and thermomechanical treatments
75.50.Bb Fe and its alloys
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

A large magnetoinductance effect in La0.67Ba0.33MnO3

V. B. Naik, A. Rebello, and R. Mahendiran

Appl. Phys. Lett. 95, 082503 (2009); http://dx.doi.org/10.1063/1.3212730 (3 pages) | Cited 1 time

Online Publication Date: 24 August 2009

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We report four probe impedance (Z = R+iX) of La0.67Ba0.33MnO3 at f = 100 kHz under different dc bias magnetic fields. The ac resistance (R) exhibits a peak around TP = 325 K which is accompanied by a rapid increase and a peak in the reactance (X) in a zero field. The magnetoreactance (ΔX/X) exhibits a sharp peak close to TP and its magnitude ( ≈ 60% in H = 1 kG) exceeds that of the ac magnetoresistance (ΔR/R = 5%). It is suggested that the magnetoreactance arises from changes in the self inductance of the sample rather than the capacitance.
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75.47.Lx Magnetic oxides
75.50.Dd Nonmetallic ferromagnetic materials

Atomically resolved Larmor frequency detection on Si(111)-7×7 oxide surface

Yasuyuki Sainoo, Hironari Isshiki, Syed Mohammad Fakruddin Shahed, Tsuyoshi Takaoka, and Tadahiro Komeda

Appl. Phys. Lett. 95, 082504 (2009); http://dx.doi.org/10.1063/1.3204688 (3 pages) | Cited 2 times

Online Publication Date: 24 August 2009

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We demonstrate that the electron spin resonance–scanning tunneling microscope can detect the Larmor frequency of a single spin with the atomic scale resolution on the oxygen-adsorbed Si(111)-7×7 surface. The spin signal from the Si dangling bond was detected on the oxygen-induced bright Si adatom with the Larmor frequency corresponding to g ∼ 2.00. However, no peak was detected on the dark adatom that is tied with an oxygen atom and the dangling bond is disappeared.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Microwave-assisted magnetization reversal in a Co/Pd multilayer with perpendicular magnetic anisotropy

Yukio Nozaki, Naoyuki Narita, Terumitsu Tanaka, and Kimihide Matsuyama

Appl. Phys. Lett. 95, 082505 (2009); http://dx.doi.org/10.1063/1.3213559 (3 pages) | Cited 19 times

Online Publication Date: 26 August 2009

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Microwave-assisted magnetization reversal in a rectangle of a Co/Pd multilayer with a perpendicular magnetic anisotropy is examined using vector network analyzer ferromagnetic resonance (FMR) spectroscopy. A microwave field is applied along the in-plane direction of the rectangle together with a negative dc easy-axis field smaller than the coercive field. Broadening or splitting of the peak profile in the FMR spectrum suggesting the formation of multidomain structure appears after the microwave field is applied. The dominance of microwave-assisted nucleation of magnetization is supported by the frequency dependence of the probability with which the multidomain structure appears.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.70.Gq Microwave and radio-frequency interactions
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Cc Other ferromagnetic metals and alloys
68.55.A- Nucleation and growth

Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions

Y. Guan, J. Z. Sun, X. Jiang, R. Moriya, L. Gao, and S. S. P. Parkin

Appl. Phys. Lett. 95, 082506 (2009); http://dx.doi.org/10.1063/1.3212870 (3 pages) | Cited 6 times

Online Publication Date: 26 August 2009

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Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel junctions (MTJs). For this purpose, T-FMR measurements were conducted with an external magnetic field up to 14 kOe applied perpendicular to the film surface of MgO-based MTJs under a dc bias. The observed frequency-field relationship suggests that a 20 Å CoFeB free layer has an effective demagnetization field much smaller than the intrinsic bulk value of CoFeB, with 4πMeff = 6.1±0.3 kOe. This value is consistent with the saturation field obtained from magnetometry measurements on extended films of the same CoFeB thickness. In-plane T-FMR on the other hand shows less consistent results for the effective demagnetization field, presumably due to excitations of more complex modes. These experiments suggest that the perpendicular T-FMR is preferred for quantitative magnetic characterization of nanoscale MTJs.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.70.Ak Magnetic properties of monolayers and thin films

A gigahertz-range spin-wave filter composed of width-modulated nanostrip magnonic-crystal waveguides

Sang-Koog Kim, Ki-Suk Lee, and Dong-Soo Han

Appl. Phys. Lett. 95, 082507 (2009); http://dx.doi.org/10.1063/1.3186782 (3 pages) | Cited 16 times

Online Publication Date: 26 August 2009

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We found a robust magnonic-crystal waveguide structure for use as an efficient gigahertz-range spin-wave filter that passes only spin waves of chosen narrow band frequencies and filters out the other frequencies. The structure consists of the serial combinations of various width modulations with different periodicities and motifs in planar-patterned thin-film nanostrips composed of a single soft magnetic material. The observed magnonic band gaps result from both the translation symmetry of the one-dimensional width modulation and the higher-quantized width-mode spin waves excited from scattering at the periodic edge-steps of the width modulation. This work brings us one step closer to practical implementations of spin waves in information transmission and processing devices.
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84.30.Vn Filters
84.40.Az Waveguides, transmission lines, striplines
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Martensitic transformation and magnetic field-induced strain in Fe–Mn–Ga shape memory alloy

T. Omori, K. Watanabe, R. Y. Umetsu, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 95, 082508 (2009); http://dx.doi.org/10.1063/1.3213353 (3 pages) | Cited 12 times

Online Publication Date: 27 August 2009

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Martensitic and magnetic properties of Fe–Mn–Ga single and polycrystalline alloys were investigated. It was found that Fe–Mn–Ga alloys exhibit martensitic transformation from the paramagnetic L21 Heusler parent phase to the ferromagnetic L10 martensite phase. The martensitic transformation temperatures increased by about 20 K by the application of a magnetic field of 7 T, and a metamagnetic phase transition was observed. In addition, a magnetic field-induced strain of 0.6% associated with magnetic field-induced forward transformation was confirmed in an Fe43Mn28Ga29 single crystal.
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81.30.Kf Martensitic transformations
75.50.Bb Fe and its alloys
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

Granular magnetoresistance in cobalt/poly (3-hexylthiophene, 2, 5-diyl) hybrid thin films prepared by a wet chemical method

Tianlong Wen, Dan Liu, Christine K. Luscombe, and Kannan M. Krishnan

Appl. Phys. Lett. 95, 082509 (2009); http://dx.doi.org/10.1063/1.3213561 (3 pages) | Cited 3 times

Online Publication Date: 27 August 2009

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Cobalt/poly (3-hexylthiophene, 2, 5-diyl) (P3HT) hybrid thin films were prepared by a wet chemical method. Their microstructure consists of a nanoscale mixture of a crystalline P3HT matrix, interspersed with amorphous P3HT regions containing the cobalt nanoparticles. Magnetic and transport measurements are consistent with this microstructure and the temperature dependence of the resistance of these hybrid systems is well-fitted (R2 = 0.9993) to the fluctuation induced tunneling model. Moreover, by applying a magnetic field, a magnetoresistance ratio of 3% was observed in 17 vol % Co hybrid films at 10 K.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
72.20.My Galvanomagnetic and other magnetotransport effects
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