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Mössbauer study of vacuum annealed Fe100-xGax (10 less - than or equal to x less - than or equal to 35) thin films

Szumiata T., Górka B., Brzózka K., Gawroński M., Gzik-Szumiata M., Javed A., Morley N. A., Gibbs M. R. J.

Nukleonika

2013

Vol. 58, No. 1

27-30

This work reports results from comparative Mossbauer studies of as-deposited and annealed Fe100.xGax (10 less - than or equal to x less - than or equal to 35) high magnetostrictive thin films of constant thickness (50 plus or minus 2 nm). Films were grown on Si(100) substrates using a co-sputtering and evaporation chamber where Fe has been sputtered and Ga was evaporated. During growth of films, a magnetic field of 65 kA/m has been applied in the plane of the film. Annealed films have been obtained by heating in vacuum for 1 h at 350 centigrade without magnetic field. After annealing, the saturation field of the Fe-Ga films has been significantly reduced. By means of the 57Fe CEMS technique the contributions from several phases have been found: Fe-Ga A2 (bcc), traces of DO3 phase, a gallium-rich disordered phase and iron oxides (both geothite and magnetite). For the sample with x = 26.5 the heat treatment reduces the DO3 phase content whereas for the film with x = 16.4 the opposite tendency has been observed. Mossbauer results were compared with XRD and MOKE findings.

Structure analysis and local magnetic parameters of magnetoresistance tunnel junctions

Kim C., Kim C. O., Hu Y., Kanak J., Stobiecki T., Ogata S., Tsunoda M., Takahashi M.

Materials Science

2003

Vol. 21, No. 1

9-23

The Magnetoresistance Tunnel Junctions (MTJ) were deposited by DC magnetron sputtering method in the following layer sequence: Ta(50A)/Cu(100A)/Ta(50A)/Ni80Fe20(20A)/Cu(50A)/Mn75Ir25(100A)/Co70Fe30(25A)/Al-O/Co70Fe30(25A)/Ni80Fe20(t) /Ta(50A)/, with t = 0A, 100A and 1000A. X-ray diffraction analysis revealed that highly oriented fcc-(111) of IrMn3, Cu, Ni80Fe20 and Co70Fe30 crystal planes are stacked parallel to the substrate plane. The improvement of (111) texture and crystallinity was observed after annealing. The tunneling magnetoresistance ratio of patterned junction with electrode layer of Ni80Fe20 (t = 1000A), deposited on the free layer of Co70Fe30 (25A) exceeds 40% at room temperature after annealing at 200°C in magnetic field 1kOe. The local hysteresis loops were measured using the magneto-optical Kerr effect system. The relatively irregular variations of coercive force Hc and unidirectional anisotropy field Hua in as-deposited sample are revealed. After 200°C annealing Hc decreases but Hua increases with smooth local variations. Two-dimensional plots of Hc and Hua show the symmetric saddle shapes with their axes aligned with the pinned layer. The distribution of surface roughness is symmetric with respect to the center of MTJ. Correlation between surface roughness and the variation of Hua suggests that the Hua variation of the free layer is well described by dipole interactions in the form of socalled Néel "orange peel" coupling.

Magnetometry of monoatomic layers and spin electronics elements

Wrona J., Stobiecki T., Czapkiewicz M., Rak R.

Materials Science

2003

Vol. 21, No. 1

55-63

In this paper, two magnetometers: resonance vibrating sample magnetometer (R-VSM) and magnetooptical Kerr effect magnetometer (MOKE) designed for hysteresis loop measurements of ultra-thin films and spintronics elements are described. Both instruments have been built by the first author of this paper in the Department of Electronics. The measuring head of R-VSM is universal and could work in the Helmholtz coils as well as in an electromagnet. The frequency of R-VSM is about 75 Hz. Test measurements on MgO(001)/Fe(4, 3, and 2ML)/50ACr samples were performed and the sensitivity was estimated as 10-5 emu. The MOKE system with differential amplifier (in contrast to lock-in detection technique) is especially recommended for rapid measurements up to 1.5 kHz. The calibration of the Kerr rotation angle was performed on the standard Fe sputtered films (with thickness from 2 nm to 50 nm) and Fe-wedge sample, prepared by MBE-technique, with the range of thickness from 1ML to 50 ML of Fe. On the base of measurement of 2, 3, 4, 5, 7 ML of Fe, the angle resolution of Kerr rotation was estimated as 0.001 min.