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ABSTRACT: The perpendicular magnetic anisotropy of sputtered CoFeB thin films covered by MgO was investigated by
vibrating sample magnetometry. Three different Cox
Fe80-xB20 alloys were studied. Under out-of plane magnetic
field, the saturation field was found to increase with increasing the Co content. The magnetization and interface
anisotropy energy were obtained for all samples. Both showed a marked dependence on the MgO overlayer
thickness. In addition, their variations were found to be non-monotonous as a function of the Co concentration.
Journal of Magnetics 03/2013; 18(1):5. · 0.66 Impact Factor
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ABSTRACT: The influence of an electric field on an ultrathin FeCo film was investigated by x-ray absorption spectroscopy and magnetic circular dichroism. Measurements were done on sub-millimeter sized pillars, with partial fluorescence yield detection. Fe L2,3 absorption spectra revealed that partial oxidation of Fe occurred during the microfabrication. The oxidation state could be reversibly controlled by an electric field, which also induced variations of the dichroic signal. These results show that electrochemical phenomena may influence the magnetism at a ferromagnet/insulator interface.
Applied Physics Letters 01/2013; 102:152401. · 3.84 Impact Factor
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ABSTRACT: We investigated spin-dependent quantum interference effects in Cr(001)/wedge Fe(001)/MgO(001)/
Fe(001) magnetic tunnel junctions by dI/dV measurements. dI/dV intensities were mapped twodimensionally as a function of applied voltage and Fe thickness, indicating a clear signature of
quantum well (QW) states in the ultrathin Fe (001) electrode. However, resonant positions of QW
states were systematically shifted by one monolayer when compared with the first-principles
calculation results. X-ray absorption spectroscopy and magnetic circular dichroism measurements
were also performed. While Fe oxide presence at Fe/MgO interface was ruled out, Fe/Cr intermixing
could not be excluded. Hence, controlling the Fe/Cr interface may affect QW state.
Applied Physics Letters 01/2013; 102:032406. · 3.84 Impact Factor
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ABSTRACT: The dependence of the magnetization and perpendicular magnetic anisotropy (PMA) of Ta/CoFeB/MgO/Ta on the thicknesses of the CoFeB layer and the MgO overlayer was investigated by vibrating sample magnetometer. The magnetization is found to be small for samples with a thin MgO overlayer. The PMA strongly depends on the MgO overlayer (hereafter, MgO) thickness and its maximum value of 1.74 erg/cm2 is achieved for a 1.0 nm thick MgO overlayer with annealing at 300 °C. The volume anisotropy of the CoFeB layer is found to be independent of the MgO thickness, which suggest that only the interface anisotropy depends on the MgO thickness. The possible mechanisms that may influence the interface magnetization and anisotropy are discussed herein.
Journal- Korean Physical Society 01/2013; · 0.45 Impact Factor
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ABSTRACT: The magnetic properties of FePd ultrathin films and their variation under the influence of an electric field are investigated by magneto-optical Kerr effect (MOKE) measurements. L10-ordered FePd shows a spin reorientation transition when varying the thickness. The easy axis of magnetization is found to be normal to the plane at thicknesses above 9 monolayers (MLs) and in-plane below 9 ML. The coercive field, the perpendicular magnetic anisotropy and the MOKE signal at saturation vary with the applied electric field. The sensitivity of the interface magnetic anisotropy is estimated to be 602 fJ/V m.
Applied Physics Letters 06/2011; 98(23):232510-232510-3. · 3.84 Impact Factor
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ABSTRACT: A voltage-induced perpendicular magnetic anisotropy change in an ultrathin FeCo layer was observed in an epitaxial magnetic tunnel junction (MTJ) structure. A spin-transfer induced ferromagnetic resonance measurement technique was used under various bias voltage applications to evaluate the anisotropy change. From the peak frequency shifts, we could estimate that a surface magnetic anisotropy change of 15 μJ/m2 was induced by an electric field application of 400 mV/nm in the MTJ with a 0.5 nm thick FeCo layer. The realization of voltage-induced anisotropy changes in an MTJ structure should have a large impact on the development of electric-field driven spintronic devices.
Applied Physics Letters 01/2010; 96(2):022506-022506-3. · 3.84 Impact Factor
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T Maruyama, Y Shiota,
T Nozaki,
K Ohta,
N Toda,
M Mizuguchi,
A A Tulapurkar,
T Shinjo,
M Shiraishi,
S Mizukami,
Y Ando,
Y Suzuki
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ABSTRACT: In the field of spintronics, researchers have manipulated magnetization using spin-polarized currents. Another option is to use a voltage-induced symmetry change in a ferromagnetic material to cause changes in magnetization or in magnetic anisotropy. However, a significant improvement in efficiency is needed before this approach can be used in memory devices with ultralow power consumption. Here, we show that a relatively small electric field (less than 100 mV nm(-1)) can cause a large change (approximately 40%) in the magnetic anisotropy of a bcc Fe(001)/MgO(001) junction. The effect is tentatively attributed to the change in the relative occupation of 3d orbitals of Fe atoms adjacent to the MgO barrier. Simulations confirm that voltage-controlled magnetization switching in magnetic tunnel junctions is possible using the anisotropy change demonstrated here, which could be of use in the development of low-power logic devices and non-volatile memory cells.
Nature Nanotechnology 04/2009; 4(3):158-61. · 27.27 Impact Factor
