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Register a new userSimulation of stress-impedance effects in low magnetostrictive films
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Added by
Bhaskar Kaviraj Mr.
Publication date
2006
fields
Physics
and research's language is
English
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A theoretical study of stress-impedance effect based on the solution of Landau-Lifsitz-Gilbert equation has been carried out. The results show that stress impedance effects depend largely on several extrinsic (external bias field, external frequency) and intrinsic (orientation and magnitude of uniaxial anisotropy, damping) parameters.
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We report an enhanced magnetoelastic contribution to the Gilbert damping in highly magnetostrictive Fe$_{0.7}$Ga$_{0.3}$ thin films. This effect is mitigated for perpendicular-to-plane fields, leading to a large anisotropy of the Gilbert damping in all of the films (up to a factor of 10 at room temperature). These claims are supported by broadband measurements of the ferromagnetic resonance linewidths over a range of temperatures (5 to 400 K), which serve to elucidate the effect of both the magnetostriction and phonon relaxation on the magnetoelastic Gilbert damping.
In this work we report the appearence of a large perpendicular magnetic anisotropy (PMA) in Fe$_{1-x}$Ga$_x$ thin films grown onto ZnSe/GaAs(100). This arising anisotropy is related to the tetragonal metastable phase in as-grown samples recently reported [M. Eddrief {it et al.}, Phys. Rev. B {bf 84}, 161410 (2011)]. By means of ferromagnetic resonance studies we measured PMA values up to $sim$ 5$times$10$^5$ J/m$^3$. PMA vanishes when the cubic structure is recovered upon annealing at 300$^{circ}$C. Despite the important values of the magnetoelastic constants measured via the cantilever method, the consequent magnetoelastic contribution to PMA is not enough to explain the observed anisotropy values in the distorted state. {it Ab initio} calculations show that the chemical ordering plays a crucial role in the appearance of PMA. Through a phenomenological model we are able to explain that an excess of next nearest neighbour Ga pairs (B$_2$-like ordering) along the perpendicular direction arises as the source of PMA in Fe$_{1-x}$Ga$_x$ thin films.
The resistive and reactive components of magneto-impedance (MI) for Finemet/Copper/Finemet sandwiched structures based on stress-annealed nanocrystalline Fe75Si15B6Cu1Nb3 ribbons as functions of different fields (longitudinal and perpendicular) and frequencies have been measured and analyzed. Maximum magneto-resistance and magneto-inductance ratios of 700% and 450% have been obtained in 30-600 kHz frequency range respectively. These large magneto-resistance and magneto-inductive ratios are a direct consequence of the large effective relative permeability due to the closed magnetic flux path in the trilayer structure. The influence of perpendicular bias fields (Hper) in the Longitudinal Magneto-impedance (LMI) configuration greatly improves the MI ratios and sensitivities. The maximum MI ratio for the resistive part increases to as large as 2500% for Hper ~ 1 Oe. The sensitivity of the magneto-resistance increases from 48%/Oe to 288%/Oe at 600 kHz frequency with the application of Hper ~ 30 Oe. Such high increase in MI ratios and sensitivities with perpendicular bias fields are due to the formation the favourable (transverse) domain structures.
Systematic measurements of stress impedance (SI) and magneto-impedance (MI) have been carried out using Co-rich amorphous ribbons of nominal composition Co71-xFexCr7Si8B14 (x = 0, 2) at various excitation frequencies and bias fields and at room temperature. The impedance, Z, for both the samples was found to be very sensitive functions of applied tensile stress (up to 100MPa) exhibiting a maximum SI ratio as much as 80% at low frequency ~ 0.1MHz. The nature of variation of impedance, Z, changes with the excitation frequency especially at higher frequencies in MHz region where it exhibits a peak. Magnetization measurements were also performed to observe the effects of applied stress and magnetization decreases with the application of stress confirming the negative magnetostriction co-efficient of both the samples. Both the samples exhibited negative magneto-impedance when the variation of Z is observed with the applied bias magnetic field, H. Maximum MI ratio as large as 99% has been observed for both the samples at low fields ~ 27Oe. The impedance as functions of applied magnetic field, Z(H), decreases with the application of stress thus making the MI curves broader. Based on the electromagnetic screening and magnetization dynamics and incorporating the Gilbert and the Bloch-Bloembergen damping and stress dependent anisotropy, the SI has been calculated and is found to describe well the stress and field dependence of impedance of the two samples.
We demonstrate reproducible voltage induced non-volatile switching of the magnetization in an epitaxial thin Fe81Ga19 film. Switching is induced at room temperature and without the aid of an external magnetic field. This is achieved by the modification of the magnetic anisotropy by mechanical strain induced by a piezoelectric transducer attached to the layer. Epitaxial Fe81Ga19 is shown to possess the favourable combination of cubic magnetic anisotropy and large magnetostriction necessary to achieve this functionality with experimentally accessible levels of strain. The switching of the magnetization proceeds by the motion of magnetic domain walls, also controlled by the voltage induced strain.
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