ABSTRACT The ferromagnetic amorphous phase in rapidly solidified Nd60Fe30Al10 glass forming alloy... more ABSTRACT The ferromagnetic amorphous phase in rapidly solidified Nd60Fe30Al10 glass forming alloys is investigated in melt spun ribbons (100 µm thick) and in chill cast cylinders (2 mm diameter). The amorphous resulting for these two different quenching rates were characterized by their room temperature hysteresis loops, magnetization and differential calorimetric measurements in the temperature range 300K-900K. The mechanical damping was explored in the 300-560 K temperature range, by measuring the internal friction and the shear modulus in a forced inverted pendulum operating in the frequency range 0.1-10Hz. Simultaneously, the electrical resistance of the samples was measured. The internal friction spectra of both, ribbons and a cylinder, exhibit a local maximum at about 500K, arising in a relaxation mechanism. After some thermal cycles the peak parameters stabilize reaching an apparent activation enthalpy of 1.5 eV and a limit relaxation time τ0 ≈ 0.4-2.5 . 10-17s. In both samples, the electrical resistance largely decreases during the first heating run to 560K and remains unchanged during subsequent thermal cycles. No changes in the elastic modulus or in the damping properties are detected at the Curie temperature of the alloys.
The glass-forming Nd60Fe30Al10 alloy, processed by melt spinning, exhibits hard magnetic properti... more The glass-forming Nd60Fe30Al10 alloy, processed by melt spinning, exhibits hard magnetic properties. For a relatively wide range of quenching rates, a single magnetic phase behavior is observed at room temperature, with coercivities between 0.1 and 0.4T. As the quenching rate decreases, the hard magnetic properties improve and the thermal stability of the resulting magnetic microstructure—as measured by the reciprocal of
FePd nanowires (NWs) with different compositions have been grown into anodized aluminum oxide tem... more FePd nanowires (NWs) with different compositions have been grown into anodized aluminum oxide templates (AAO) by AC electrodeposition at room temperature. The effects of nanowire composition and morphology on the hysteresis properties of the ordered array of NWs are investigated. All the NWs are polycrystalline; the Fe-rich wires have a bcc structure while the Pd rich ones are fcc. FePd NWs are ferromagnetic and the spontaneous magnetization is found to be parallel to the nanowire long axis (out of plane easy axis) and both, the saturation polarization and the coercive field increase with the iron content.
The magnetic microstructures and the magnetization mechanisms operating in melt spun Nd 60 Fe 30 ... more The magnetic microstructures and the magnetization mechanisms operating in melt spun Nd 60 Fe 30 Al 10 hard magnetic alloys, are investigated by Mössbauer Effect spectroscopy and by room temperature magnetic relaxation measurements. It is found that small ferromagnetic crystalline clusters, identified as a μ-type metastable phase of the NdFeAl system, develop in the matrix as the quenching rate decreases. For the alloys quenched at lower rates, the magnetic relaxation parameters measured -the mean fluctuation field μ 0 H f and apparent activation volume v ac -are practically constant near the coercivity; they are consistent with a granular magnetization mechanism, involving 'magnetic grains' containing about 25 clusters, further supporting a model of cluster superferromagnetism. For higher cooling rates, the activation volume increases with the applied field suggesting a different magnetic microstructure; even when the experimental data can not be systematized by a mechani...
ABSTRACT The ferromagnetic amorphous phase in rapidly solidified Nd60Fe30Al10 glass forming alloy... more ABSTRACT The ferromagnetic amorphous phase in rapidly solidified Nd60Fe30Al10 glass forming alloys is investigated in melt spun ribbons (100 µm thick) and in chill cast cylinders (2 mm diameter). The amorphous resulting for these two different quenching rates were characterized by their room temperature hysteresis loops, magnetization and differential calorimetric measurements in the temperature range 300K-900K. The mechanical damping was explored in the 300-560 K temperature range, by measuring the internal friction and the shear modulus in a forced inverted pendulum operating in the frequency range 0.1-10Hz. Simultaneously, the electrical resistance of the samples was measured. The internal friction spectra of both, ribbons and a cylinder, exhibit a local maximum at about 500K, arising in a relaxation mechanism. After some thermal cycles the peak parameters stabilize reaching an apparent activation enthalpy of 1.5 eV and a limit relaxation time τ0 ≈ 0.4-2.5 . 10-17s. In both samples, the electrical resistance largely decreases during the first heating run to 560K and remains unchanged during subsequent thermal cycles. No changes in the elastic modulus or in the damping properties are detected at the Curie temperature of the alloys.
The glass-forming Nd60Fe30Al10 alloy, processed by melt spinning, exhibits hard magnetic properti... more The glass-forming Nd60Fe30Al10 alloy, processed by melt spinning, exhibits hard magnetic properties. For a relatively wide range of quenching rates, a single magnetic phase behavior is observed at room temperature, with coercivities between 0.1 and 0.4T. As the quenching rate decreases, the hard magnetic properties improve and the thermal stability of the resulting magnetic microstructure—as measured by the reciprocal of
FePd nanowires (NWs) with different compositions have been grown into anodized aluminum oxide tem... more FePd nanowires (NWs) with different compositions have been grown into anodized aluminum oxide templates (AAO) by AC electrodeposition at room temperature. The effects of nanowire composition and morphology on the hysteresis properties of the ordered array of NWs are investigated. All the NWs are polycrystalline; the Fe-rich wires have a bcc structure while the Pd rich ones are fcc. FePd NWs are ferromagnetic and the spontaneous magnetization is found to be parallel to the nanowire long axis (out of plane easy axis) and both, the saturation polarization and the coercive field increase with the iron content.
The magnetic microstructures and the magnetization mechanisms operating in melt spun Nd 60 Fe 30 ... more The magnetic microstructures and the magnetization mechanisms operating in melt spun Nd 60 Fe 30 Al 10 hard magnetic alloys, are investigated by Mössbauer Effect spectroscopy and by room temperature magnetic relaxation measurements. It is found that small ferromagnetic crystalline clusters, identified as a μ-type metastable phase of the NdFeAl system, develop in the matrix as the quenching rate decreases. For the alloys quenched at lower rates, the magnetic relaxation parameters measured -the mean fluctuation field μ 0 H f and apparent activation volume v ac -are practically constant near the coercivity; they are consistent with a granular magnetization mechanism, involving 'magnetic grains' containing about 25 clusters, further supporting a model of cluster superferromagnetism. For higher cooling rates, the activation volume increases with the applied field suggesting a different magnetic microstructure; even when the experimental data can not be systematized by a mechani...
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