ABSTRACT It has been shown that both pinning- (mechanical) and reordering-induced (chemical) stab... more ABSTRACT It has been shown that both pinning- (mechanical) and reordering-induced (chemical) stabilization components contribute to the overall stabilization effect. An algorithm has been developed for quantitative analysis of the chemical and mechanical stabilization components, using routine calorimetry results. The basic idea underlying this algorithm is that chemical and mechanical stabilization components stem, respectively, from the factors, affecting thermodynamically reversible and irreversible factors during the first reverse transformation of the stabilized martensite. On a thermodynamical level, application of the suggested algorithm has been illustrated using experimental calorimetry results for a Cu–Zn–Al alloy. Here we report analysis of pinning and reordering processes on a microscopic scale, using experimental data on non-linear anelasticity in the same Cu–Zn–Al alloy to track different spatial and temporal localization of these processes during martensite ageing.
We have used a recently designed mechanomagnetic spectroscopy technique to study the inverse magn... more We have used a recently designed mechanomagnetic spectroscopy technique to study the inverse magnetoelastic effect (stress-induced magnetization) in ferromagnetic materials simultaneously with their elastic and anelastic properties. Special attention has been paid to ferromagnetic shape memory alloys. Application of mechanomagnetic spectroscopy technique allows one to study the stress-induced motion of elastic (by means of the anelasticity measurements) and magnetic domain boundaries (through the detection of the stress-induced magnetization). The experimental technique is based on the piezoelectric ultrasonic composite oscillator technique with an additional magnetic channel, enabling to register the induction, produced by the strain of a ferromagnetic sample, down to 10 −10 T. Examples of application of this new technique are given, which include observation of a temperature-magnetic field domain wherein magnetoelastic coupling demonstrates variations of sign and analysis of magnetic domain wall dynamics in polycrystalline ferromagnetic martensites.
A magnetic anomaly in the austenitic state of Ni51.5Fe21.5Ga27 single crystalline ferromagnetic s... more A magnetic anomaly in the austenitic state of Ni51.5Fe21.5Ga27 single crystalline ferromagnetic shape memory alloy has been studied by means of ac impedance measurements. A much stronger effect of the degree of atomic order on the temperature of this anomaly (as compared to the temperature of the martensitic and para-ferromagnetic transitions) has been found. It has been shown that apart from the previously reported slight variation in the saturation magnetization, the magnetic anomaly results in a nearly one order of magnitude change in the value of initial magnetic permeability. The anomaly is not revealed in the resistive impedance at low frequencies, pointing likely to its purely magnetic origin.
We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase... more We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase transition the direct transition from ferromagnetic austenite to nonmagnetic martensite is isothermal. In contrast to the direct transformation, the reverse one (nonmagnetic martensite–ferromagnetic austenite) is athermal, just as are athermal both direct and reverse martensitic transformations in conventional ferromagnetic shape memory alloys. The observed asymmetry of properties of the direct and reverse phase transitions in metamagnetic alloys, together with the data on entropy change during the magnetostructural transition, evidences that the magnetostructural transition is driven by the first order lattice modification. The change in magnetic ordering is an effect accompanying the lattice modification, opposing the direct transformation and promoting the reverse one. It has been shown that relaxation effects in metamagnetic shape memory alloys are intrinsic in the direct transforma...
Results are reported for simultaneous experimental studies of the stress-induced magnetic inducti... more Results are reported for simultaneous experimental studies of the stress-induced magnetic induction and of anelasticity in a polycrystalline Ni–Fe–Ga ferromagnetic shape memory alloy. The authors found in the martensitic state a linear relationship between mechanically induced induction and stress amplitude, in contrast to a strong nonlinearity of the anelastic strain. This difference between elastic and magnetic responses to applied stress points to inefficient coupling between the motion of elastic twins/domain boundaries and magnetic domain walls. They argue that, in acoustic experiments, magnetic domain walls in Ni–Fe–Ga polycrystals perform only linear displacements within local potential minima, characteristic for the microeddy current magnetomechanical damping.
We studied the entropy change and the shift of the martensitic transformation temperatures with m... more We studied the entropy change and the shift of the martensitic transformation temperatures with magnetic field in samples of a polycrystalline Ni–Co–Mn–In alloy having different degrees of long-range atomic order due to different heat treatments. We found, for the samples of the same composition, strong variations of the entropy change with the degree of atomic order, mediated by the difference between the Curie and martensitic transformation temperatures. Calculations of the field-induced shift of the transformation using data of entropy variations show good agreement with experimental results.
ABSTRACT A technique referred to as mechanomagnetic spectroscopy, which combines the resonant pie... more ABSTRACT A technique referred to as mechanomagnetic spectroscopy, which combines the resonant piezoelectric composite oscillator technique with measurements of the periodic stress-induced magnetization of ferromagnetic samples has been applied to study the magnetoelastic coupling in Ni51.5Fe21.5Ga27 single crystals. The composition selected demonstrates a martensitic transformation from the high-temperature cubic phase to the tetragonal one well separated from the para-ferromagnetic transition, allowing studying the high-temperature parent phase in the ferromagnetic state. Measurements were performed at fixed temperatures and oscillatory strain amplitudes as a function of periodic polarizing field and as a function of temperature for fixed values of applied magnetic field and strain amplitude. It has been found that the reversible inverse magnetostriction changes its sign in the cubic phase for the 〈1 0 0〉 orientation, first close to the Curie temperature and then also over a certain range of temperatures below that. This anomaly is not present for the 〈1 1 1〉 orientation. A possible origin of these peculiarities is discussed under the localized magnetic moment assumption.
ABSTRACT It has been shown that both pinning- (mechanical) and reordering-induced (chemical) stab... more ABSTRACT It has been shown that both pinning- (mechanical) and reordering-induced (chemical) stabilization components contribute to the overall stabilization effect. An algorithm has been developed for quantitative analysis of the chemical and mechanical stabilization components, using routine calorimetry results. The basic idea underlying this algorithm is that chemical and mechanical stabilization components stem, respectively, from the factors, affecting thermodynamically reversible and irreversible factors during the first reverse transformation of the stabilized martensite. On a thermodynamical level, application of the suggested algorithm has been illustrated using experimental calorimetry results for a Cu–Zn–Al alloy. Here we report analysis of pinning and reordering processes on a microscopic scale, using experimental data on non-linear anelasticity in the same Cu–Zn–Al alloy to track different spatial and temporal localization of these processes during martensite ageing.
We have used a recently designed mechanomagnetic spectroscopy technique to study the inverse magn... more We have used a recently designed mechanomagnetic spectroscopy technique to study the inverse magnetoelastic effect (stress-induced magnetization) in ferromagnetic materials simultaneously with their elastic and anelastic properties. Special attention has been paid to ferromagnetic shape memory alloys. Application of mechanomagnetic spectroscopy technique allows one to study the stress-induced motion of elastic (by means of the anelasticity measurements) and magnetic domain boundaries (through the detection of the stress-induced magnetization). The experimental technique is based on the piezoelectric ultrasonic composite oscillator technique with an additional magnetic channel, enabling to register the induction, produced by the strain of a ferromagnetic sample, down to 10 −10 T. Examples of application of this new technique are given, which include observation of a temperature-magnetic field domain wherein magnetoelastic coupling demonstrates variations of sign and analysis of magnetic domain wall dynamics in polycrystalline ferromagnetic martensites.
A magnetic anomaly in the austenitic state of Ni51.5Fe21.5Ga27 single crystalline ferromagnetic s... more A magnetic anomaly in the austenitic state of Ni51.5Fe21.5Ga27 single crystalline ferromagnetic shape memory alloy has been studied by means of ac impedance measurements. A much stronger effect of the degree of atomic order on the temperature of this anomaly (as compared to the temperature of the martensitic and para-ferromagnetic transitions) has been found. It has been shown that apart from the previously reported slight variation in the saturation magnetization, the magnetic anomaly results in a nearly one order of magnitude change in the value of initial magnetic permeability. The anomaly is not revealed in the resistive impedance at low frequencies, pointing likely to its purely magnetic origin.
We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase... more We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase transition the direct transition from ferromagnetic austenite to nonmagnetic martensite is isothermal. In contrast to the direct transformation, the reverse one (nonmagnetic martensite–ferromagnetic austenite) is athermal, just as are athermal both direct and reverse martensitic transformations in conventional ferromagnetic shape memory alloys. The observed asymmetry of properties of the direct and reverse phase transitions in metamagnetic alloys, together with the data on entropy change during the magnetostructural transition, evidences that the magnetostructural transition is driven by the first order lattice modification. The change in magnetic ordering is an effect accompanying the lattice modification, opposing the direct transformation and promoting the reverse one. It has been shown that relaxation effects in metamagnetic shape memory alloys are intrinsic in the direct transforma...
Results are reported for simultaneous experimental studies of the stress-induced magnetic inducti... more Results are reported for simultaneous experimental studies of the stress-induced magnetic induction and of anelasticity in a polycrystalline Ni–Fe–Ga ferromagnetic shape memory alloy. The authors found in the martensitic state a linear relationship between mechanically induced induction and stress amplitude, in contrast to a strong nonlinearity of the anelastic strain. This difference between elastic and magnetic responses to applied stress points to inefficient coupling between the motion of elastic twins/domain boundaries and magnetic domain walls. They argue that, in acoustic experiments, magnetic domain walls in Ni–Fe–Ga polycrystals perform only linear displacements within local potential minima, characteristic for the microeddy current magnetomechanical damping.
We studied the entropy change and the shift of the martensitic transformation temperatures with m... more We studied the entropy change and the shift of the martensitic transformation temperatures with magnetic field in samples of a polycrystalline Ni–Co–Mn–In alloy having different degrees of long-range atomic order due to different heat treatments. We found, for the samples of the same composition, strong variations of the entropy change with the degree of atomic order, mediated by the difference between the Curie and martensitic transformation temperatures. Calculations of the field-induced shift of the transformation using data of entropy variations show good agreement with experimental results.
ABSTRACT A technique referred to as mechanomagnetic spectroscopy, which combines the resonant pie... more ABSTRACT A technique referred to as mechanomagnetic spectroscopy, which combines the resonant piezoelectric composite oscillator technique with measurements of the periodic stress-induced magnetization of ferromagnetic samples has been applied to study the magnetoelastic coupling in Ni51.5Fe21.5Ga27 single crystals. The composition selected demonstrates a martensitic transformation from the high-temperature cubic phase to the tetragonal one well separated from the para-ferromagnetic transition, allowing studying the high-temperature parent phase in the ferromagnetic state. Measurements were performed at fixed temperatures and oscillatory strain amplitudes as a function of periodic polarizing field and as a function of temperature for fixed values of applied magnetic field and strain amplitude. It has been found that the reversible inverse magnetostriction changes its sign in the cubic phase for the 〈1 0 0〉 orientation, first close to the Curie temperature and then also over a certain range of temperatures below that. This anomaly is not present for the 〈1 1 1〉 orientation. A possible origin of these peculiarities is discussed under the localized magnetic moment assumption.
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Papers by Miquel Corro