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15 Nov 2005

Volume 98, Issue 10, Articles (10xxxx)

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Reduction of Curie temperature and saturation magnetization in Ba2−xNaxFeMoO6

Koji Yoshida, Yuki Fujii, and Hajime Shimizu

J. Appl. Phys. 98, 103901 (2005); http://dx.doi.org/10.1063/1.2131205 (4 pages) | Cited 2 times

Online Publication Date: 16 November 2005

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We investigated the role of carrier electrons on ferromagnetism in a half-metallic double perovskite Ba2FeMoO6 by means of a partial substitution of Na+ for Ba2+. Single-phase samples of Ba2−xNaxFeMoO6 are synthesized up to x = 0.6. The nonmetallic upturn in resistivity appears with the Na substitution, suggesting a reduction of the carrier doping level. Because of the observed decrease of both magnetoresistance and Curie temperature with x, the Na substitution negatively works for applicative performance. We will show, however, that the observed decrease of the saturation moment with x is of importance to advance understanding for the stabilization of ferromagnetism.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
61.72.S- Impurities in crystals
75.47.Pq Other materials

Modulated optical reflectance measurements on La2/3Sr1/3MnO3 thin films

Laurence Méchin, Stéphane Flament, Andy Perry, Darryl P. Almond, and Radoslav A. Chakalov

J. Appl. Phys. 98, 103902 (2005); http://dx.doi.org/10.1063/1.2128693 (7 pages) | Cited 2 times

Online Publication Date: 18 November 2005

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The modulated optical reflectance (MOR) measurement technique was applied to colossal magnetoresistive materials, in particular, La2/3Sr1/3MnO3 (LSMO) thin films. The contactless measurement scheme is prospective for many applications spanning from materials’ characterization to devices such as reading heads for magnetically recorded media. A contrasted room-temperature surface scan of a 100-μm-wide and 400-μm-long bridge patterned into LSMO film provided preliminary information about the film homogeneity. Then the temperature was varied between 240 and 400 K, i.e., through the ferromagnetic to paramagnetic transition. A clear relation between the MOR signal measured as a function of the temperature and the relative derivative of the resistivity up to the Curie temperature was observed. This relationship is fundamental for the MOR technique and its mechanism was explored in the particular case of LSMO. Analysis in the framework of the Drude model showed that, within certain conditions, the measured MOR signal changes are correlated to the changes in the charge-carrier concentration.
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78.66.Nk Insulators
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Critical exponents of the La0.7Sr0.3MnO3, La0.7Ca0.3MnO3, and Pr0.7Ca0.3MnO3 systems showing correlation between transport and magnetic properties

Subhrangsu Taran, B. K. Chaudhuri, Sandip Chatterjee, H. D. Yang, S. Neeleshwar, and Y. Y. Chen

J. Appl. Phys. 98, 103903 (2005); http://dx.doi.org/10.1063/1.2128467 (6 pages) | Cited 17 times

Online Publication Date: 18 November 2005

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From the low-temperature (down to 10 K) dc-magnetization data of the La0.7Sr0.3MnO3 (LSM), La0.7Ca0.3MnO3 (LCM), and Pr0.7Ca0.3MnO3 (PCM) systems, we estimated the critical exponents β, γ, and hence δ from the analysis of the modified Arrot plots. The exponent β estimated for the LCM system is less than that predicted by Heisenberg model and resides within the zone predicted by Ising model while for the LSM sample, β is higher than that predicted from the Heisenberg model which is considered to be due to the presence of dipole-dipole interaction arising from the large spin moment in the LSM system. The magnetization data of the PCM system cannot be fitted to the modified Arrot plots, which suggest highly inhomogeneous ground state even under 5 T magnetic field. Both LSM and LCM have almost equal values of γ. Seebeck coefficient data indicate a crossover from higher-temperature n-type to lower-temperature p-type conductivity behavior in both LSM and LCM systems, while the semiconducting PCM system shows p-type conductivity throughout the temperature range (300–80 K). It is noticed that for LSM system TC (Curie temperature) and TMI (metal-insulator transition temperature) are almost equal ( ∼ 360 K), whereas for the LCM system there exist a large difference between TC and TMI (TC ∼ 245 K and TMI ∼ 265 K), which may give some idea regarding the critical behavior of the respective samples.
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75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
72.20.Pa Thermoelectric and thermomagnetic effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.30.+h Metal-insulator transitions and other electronic transitions

Switching of submicron-sized, antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers

N. Wiese, T. Dimopoulos, M. Rührig, J. Wecker, and G. Reiss

J. Appl. Phys. 98, 103904 (2005); http://dx.doi.org/10.1063/1.2132509 (5 pages) | Cited 4 times

Online Publication Date: 21 November 2005

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This work reports on the magnetic reversal of submicron-sized elements consisting of an CoFeB/Ru/CoFeB artificial ferrimagnet (AFi). The elements were patterned into ellipses having a width of approximately 250–270 nm and a varying aspect ratio between 1.3 and 8. The coercivity was found to decrease with an increasing imbalance of the magnetic moment of the two antiferromagnetically coupled layers and is therefore strongly affected by an increase of effective anisotropy due to the antiferromagnetic coupling of the two layers. With respect to a single layer of amorphous CoFeB, patterned in comparable elements, the AFi has an increased coercivity. Switching asteroids comparable to single layers were only observed for samples with a high net moment.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy

Effect of aluminum substitution on microwave absorption properties of barium hexaferrite

Jianxun Qiu, Qiguo Zhang, Mingyuan Gu, and Haigen Shen

J. Appl. Phys. 98, 103905 (2005); http://dx.doi.org/10.1063/1.2135412 (5 pages) | Cited 8 times

Online Publication Date: 23 November 2005

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Aluminum substituted barium hexaferrites were prepared by the self-propagating combustion method and subsequent calcination at 850 °C. The crystalline structure, complex permittivity, complex permeability, and hyperfine parameters of BaFe12−xAlxO19 (x varies from 1.5 to 2.3 in steps of 0.2) were measured with x-ray diffraction (XRD), vector network analyzer and Mössbauer spectroscopy. The XRD results show that all Al3+ ions enter into the lattice of hexagonal barium ferrite. The substitution of Al3+ ions can greatly affect the complex permittivity and permeability of barium ferrite. With increasing substitution, the real part of complex permittivity increases gradually, and the peaks of the imaginary part of complex permeability shift into higher frequency band. When the substitution amount x is 1.9, the largest movement of the peaks is 1.95 GHz, which indicates that the ferromagnetic resonant frequency of barium ferrite increases by 1.95 GHz. The Al3+ ions preferentially occupy the 4f2, 2a, 4f1, and 12k sites in the subcrystalline structure up to x = 1.9, and then the Al3+ ions mainly occupy 12k sites. This change also results in 2b sites with a large quadrupole splitting. These occupations lead to a variable magnetocrystalline anisotropy field.
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75.50.Ww Permanent magnets
75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds
71.70.Jp Nuclear states and interactions
76.80.+y Mössbauer effect; other γ-ray spectroscopy
77.22.Ch Permittivity (dielectric function)
81.05.Cy Elemental semiconductors
81.40.Gh Other heat and thermomechanical treatments
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