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15 May 2000

Volume 76, Issue 20, pp. 2815-2963

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Evidence for valence fluctuation of Fe in Sr2FeMoO6−w double perovskite

J. Lindén, T. Yamamoto, M. Karppinen, H. Yamauchi, and T. Pietari

Appl. Phys. Lett. 76, 2925 (2000); http://dx.doi.org/10.1063/1.126518 (3 pages) | Cited 62 times

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In this letter evidence for the formation of a valence-fluctuation state of iron, formally denoted as Fe2.5+, is presented. The system under study is the Sr2FeMoO6−w double perovskite, known for exhibiting a very large magnetoresistance. Samples of Sr2FeMoO6−w were synthesized by means of an encapsulation technique utilizing an Fe getter technique and characterized by 57Fe Mössbauer spectroscopy. From 5 K to room temperature the Mössbauer spectrum is dominated by a component with hyperfine parameter values between those expected for high-spin Fe3+ and high-spin Fe2+. © 2000 American Institute of Physics.
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71.28.+d Narrow-band systems; intermediate-valence solids
76.80.+y Mössbauer effect; other γ-ray spectroscopy
71.70.Jp Nuclear states and interactions

Magnetic moment of Mn in the ferromagnetic semiconductor (Ga0.98Mn0.02)As

H. Ohldag, V. Solinus, F. U. Hillebrecht, J. B. Goedkoop, M. Finazzi, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 76, 2928 (2000); http://dx.doi.org/10.1063/1.126519 (3 pages) | Cited 54 times

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We have studied the quasibinary ferromagnetic semiconductor (Ga0.98Mn0.02)As by magnetic circular dichroism in x-ray absorption. We find a richly structured Mn absorption spectrum typical for localized 3d electrons. An analysis of the magnetization-averaged and dichroism line shapes shows a local Mn moment of 4.6μB, which is close to the Hund’s rule moment for the half-filled 3d shell. The magnitude of the dichroism reveals that only about 1/7 of the Mn atoms participate in the ferromagnetic order. Our experiment does not show a distinction between the ferro- and paramagnetic Mn atoms. © 2000 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic domain and domain-wall imaging of submicron Co dots by probing the magnetostrictive response using atomic force microscopy

J. Wittborn, K. V. Rao, J. Nogués, and Ivan K. Schuller

Appl. Phys. Lett. 76, 2931 (2000); http://dx.doi.org/10.1063/1.126520 (3 pages) | Cited 6 times

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An approach to image the domains and domain walls of small ferromagnetic entities using atomic force microscopy (AFM), with a nonmagnetic AFM probe, has been developed. Exciting the sample in an external ac magnetic field, the distribution of magnetostrictive response at the surface is detected. By this technique, the domains and domain walls of submicron Co dots have been imaged with a 1 nm lateral resolution. In elliptical Co dots with a 350-nm-long axis on a triangular lattice array with 400 nm periodicity, we find evidence for two domains with opposite magnetization orientation across a wall. The domain-wall width in these dots is found to be about 35 nm. Furthermore, we observe a ferromagnetic alignment of the domains in the neighboring dots, which suggests a magnetostatic interaction among the dots. © 2000 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
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