Magnetic transition in nanocrystalline soft magnetic alloys analyzed via ac inductive techniques

Abstract

The magnetic transition in a FeSiBCuNb nanocrystalline alloy, associated with the decoupling of ferromagnetic crystallites around the Curie point of the residual amorphous matrix, is analyzed in this work through the temperature dependence of the ac axial magnetic permeability and impedance of the samples. The temperature dependence of both complex magnitudes presents a maximum in the irreversible contribution at a certain transition temperature. While for low values of the exciting ac magnetic field the transition temperature lies below the Curie temperature of the amorphous phase, a shift above this Curie point is observed increasing the amplitude of the applied ac magnetic field. The detected field dependence is interpreted taking into account the ac nature of the inductive characterization techniques and the actual temperature dependence of the coercivity of the samples.

Magnetic properties of Mn-doped finemet nanocrystalline alloy

“…increase and decrease in m r and m i ; respectively) together with the previously detected enhancement of T Ca : On the other hand, the precipitation of the BCC-Fe rich nanocrystals (T m 4550 1C; see Fig. 2b) promotes a different mðTÞ evolution, in particular, the occurrence of a well-defined maximum in m i that should be correlated with the characteristic temperature dependence of the sample coercivity, H C [7]. In these nanocrystalline samples, a progressive magnetic hardening with T is experimentally detected around T Ca and associated with the magnetic decoupling of ferromagnetic crystallites.…”

Impedance and initial magnetic permeability of gadolinium

“…Indeed, certain magnetic phase transitions generate intrinsic impedance effect below T C that may be quite strong. 13 Impedance experiments have also been used to study magnetic transitions in nanocrystalline soft magnetic alloys 14 and were employed as an auxiliary experimental technique to detect weak-order magnetic or structural transitions. 15 The impedance Z͑ ͒ is the response function of a conductor submitted to an alternate electric current I͑ ͒ so that V͑ ͒ = Z͑ ͒I͑ ͒, where V͑ ͒ is the voltage drop between two points at the surface of the sample.…”

Magnetic properties of Fe-based soft magnetic nanocrystalline alloys

“…freezing temperature of spin-glasses or blocking temperature in superparamagnetic nanoparticles). Its occurrence in the present case should be ascribed to the magnetic decoupling between the ferromagnetic crystallites around T C,a [9,11]. The most striking experimental fact is the shift of T P towards higher measuring temperatures with the amplitude of the exciting magnetic field, H ac .…”

“…The applications of these soft magnetic alloys demand optimum soft magnetic behavior and stable structural and magnetic characteristics at the desired working temperature. On the other hand, some striking features are experimentally detected when the magnetic transition is analyzed via ac inductive techniques (magnetic permeability and electrical impedance) [11,12]. In particular, the occurrence of a maximum value in the irreversible contribution at the decoupling temperature, T P , is detected that shifts towards higher measuring temperatures with the amplitude of the exciting magnetic field.…”

“…Thus, the magnetic transition is experimentally detected as a sharp increase and decrease, respectively, of the coercivity and the magnetic permeability around T C,a. [7,11].…”