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Measurements of temperature dependence of AC-susceptibility were made in Fe–30.2at.%Ni Invar alloy before and after 100 MeV Xe ion irradiation up to the dose of 1014 ions/cm2. Measurements were performed at various angles θ between the direction of the ion beam and the external AC-magnetic field. It was found that in partially irradiated area, locally ferromagnetic parts exist at temperatures above the Curie temperature of the body where high-energy ions did not penetrate. The easy axis of the locally ferromagnetic parts was determined to be parallel to the beam direction. Those locally ferromagnetic parts can be considered to be in thin needle-like shape. This type of modification has a possibility of applications for perpendicular high-density memory and giant magneto-resistance materials. [Copyright &y& Elsevier]

Abstract: Effect of high-energy heavy-ion irradiation on Fe-based invar alloys such as Fe–Ni, Fe–Pd and Fe–Pt alloys have been intensively investigated. A large increase of the Curie temperature of about 100K has been found in Fe–Ni invar alloys, while in Fe–Pd invar alloys a medium increase of about 30K was detected. On the contrary, a decrease of about 15K was observed in Fe–Pt invar alloys. Those differences in the irradiation effects are interpreted considering at least two competing physical origins. [Copyright &y& Elsevier]

Abstract: Fe50Ni37Mn13, which is a ferromagnetic alloy with FCC crystal structure, has been reported to show the Invar effect below the Curie temperature; however, this alloy shows a typical anti-Invar effect above the Curie temperature. In this paper, we discuss the pressure dependence of the temperature variation of the alternative current (AC) susceptibility at a frequency of 1kHz for Fe50Ni37Mn13 at various pressures up to 7.5GPa above 77K; we then compare the results with those for Fe68.1Ni31.9, which were obtained in a previous study. Fe50Ni37Mn13 was in a ferromagnetic state throughout the entire pressure range measured. T C decreases in inverse proportion to the increasing pressure; dT C/dp and dln T C/dp for Fe50Ni37Mn13 are −26KGPa−1 and −0.07GPa−1, respectively. Further, the temperature variation of the shape of the χ′–T curve for different pressures indicates continuous combining of magnetic interactions occurs at high pressures. These results are similar to those obtained for Fe68.1Ni31.9. [Copyright &y& Elsevier]

Abstract: Ion irradiation effects on magnetic properties in Fe–Ni alloy thin films are studied. The specimens of Fe–Ni alloy thin films (∼500nm in thickness) are irradiated at room temperature with several kinds of ions in the energy and mass ranges of 1.0–200MeV and 1H–197Au. A large increase in T C is observed for comparatively lower energy and lighter ion irradiation. These results suggest that the dominant energy transfer process for the modification of magnetic properties in Fe–Ni alloys is the elastic interaction between incident ions and target atoms. The dependence on ion energy, mass and fluence of the change in T C gives information on a dominant irradiation parameter. [Copyright &y& Elsevier]

Abstract: AC susceptibility measurements in mechanically alloyed (MA) Ni–20at% Mn were made under hydrostatic pressures up to 7.5GPa. The results were compared with a bulk alloy made by the conventional method of melting. The Curie temperature decreased with pressure at the rate of −6.9 and −8.0K/GPa in MA and the bulk alloy, respectively. The transition temperature to the reentrant spin glass state increased at the rate of 1.2 and 1.7K/GPa in MA and the bulk alloy, respectively. The results were explained by assuming a Gaussian distribution of concentration fluctuation. [Copyright &y& Elsevier]

Abstract: Pressure dependence of the irradiation-induced ferromagnetism recently found in Fe–Ni invar alloys was investigated under hydrostatic pressures up to 7.5GPa. A rectangular sheet of Fe–30.2at% Ni invar alloy was irradiated with 80MeV Xe ions. The range was much smaller than the thickness of the sample. The Curie temperature of the irradiated part increased by 63K, and the absolute value of the pressure coefficient, dT C/dp was smaller than that of non-irradiated part. The relation holds with for both non-irradiated and irradiated part. The itinerant character was not so much modified by irradiation. [Copyright &y& Elsevier]

The magnetic properties of an ordered Fe72.8Pt27.2 Invar alloy have been investigated under high pressures up to 7.5 GPa by AC susceptibility measurements in the temperature range from 4.2 to 430 K. The Curie temperature decreased with increasing pressure and then the ferromagnetic state vanished above 6.5 GPa. A new high-pressure magnetic phase appeared at 3.5 GPa in the low temperature range below 40 K, which is quiet different from the high-pressure phase observed in disordered Fe–Pt and Fe–Ni Invar alloys. The transition temperature to this new phase increased with pressure and the new phase became more stable. This tendency resembles to the feature expected by a recent theoretical calculation. [Copyright &y& Elsevier]

The magnetic properties of an FCC Fe68.1Ni31.9 Invar alloy have been investigated under high pressure up to 7.7 GPa by AC susceptibility measurements in the temperature range from 4.2 to 400 K. Up to 5.5 GPa, the Curie temperature (TC) decreased linearly with increasing pressure. Above 3.5 GPa, a reentrant spin glass-like phase was observed clearly in the low-temperature region below 50 K. Above 5.5 GPa, ferromagnetic (FM) phase began to collapse with increasing pressure, and then at 7.7 GPa, FM phase disappeared, while the spin glass-like phase was still seen. Our results dearly show the pressure induced magnetic phase transition from the FM phase to the spin glass-like high-pressure magnetic phase. [Copyright &y& Elsevier]

Fe0.68Ni0.32 Invar alloys are irradiated with 3.54 GeV Xe ions, and with 2.71 GeV U ions at room temperature. Measurements of the magnetic moment of specimens under AC magnetic field before and after irradiation show that the Curie temperature, Tc, for the irradiated region increases with increasing the ion fluence. This phenomenon appears even at low ion fluence, implying that it is attributed to ion-induced high-density electronic excitation. It is well known that Tc of such Fe–Ni Invar alloys strongly depends on the Ni concentration and the external pressure. With increasing the Ni concentration from ∼30%, Tc increases, and with decreasing the lattice parameter by the external pressure, Tc decreases. Therefore, the increase in Tc by high-energy ion irradiation can be explained as originating from the lattice expansion and/or the composition change, which are induced by the high-density electronic excitation. [Copyright &y& Elsevier]

Abstract: The pressure effect on the Curie temperature T C of the Heusler alloys Ni2MnZ (Z=Ga, Sn and Sb) has been investigated by measuring the temperature dependence of initial permeability at various pressures up to 100kbar. It was found that the Curie temperature of Ni2MnZ (Z=Ga, Sn and Sb) increases almost linearly with increasing pressure and then shows the tendency of saturation at high pressure. The pressure derivatives of T C in the pressure range below about 60kbar were estimated to be 0.36K/kbar for Ni2MnGa, 0.68K/kbar for Ni2MnSn. The value of dT C/dp at 5kbar for Ni2MnSb was estimated to be ∼1.2K/kbar. [Copyright &y& Elsevier]