Characterization of Magnetic Transformation at Curie Temperature in Finemet-type Microwires by DSC
- PDF / 210,310 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 0 Downloads / 163 Views
Characterization of Magnetic Transformation at Curie Temperature in Finemet-type Microwires by DSC Sergey Kaloshkin 1, Margarita Churyukanova 1, Victor Tcherdyntsev 1 National University of Science and Technology «MISIS», Leninsky prosp., 4, Moscow, 119049, Russia
1
ABSTRACT Finemet-type amorphous alloys are good soft magnetic materials due to their amorphousnanocrystalline structure with close to zero magnetostriction. A very sensitive method for controlling relaxation and crystallization processes in such alloys is proposed. It consists in precise DSC measurements of heat capacity peak in the vicinity of the Curie temperature TC. Time-temperature dependencies of TC for microwires in comparison with ribbon shaped amorphous alloys were studied. Relaxation of atomic structure of amorphous phase during annealing was accompanied by an increase of TC. ı-shaped time dependencies are characterized by at least two relaxation processes, corresponding apparent values of activation energy were estimated. Decomposition of amorphous phase and redistribution of components between amorphous phase and growing nanocrystals affect the shape and position of the DSC peak at TC as well. Study of microwires with glass coating revealed the influence of internal stress on the shape and position of the Curie peak on DSC curve: increase of internal strain tensions leads to suppression of the TC peak. INTRODUCTION Nanocrystalline Finemet-type materials attract much attention due to their outstanding soft magnetic properties combining high permeability with relatively high magnetization and giant magnetic impedance (GMI) effect [1, 2]. Development of sensitivity and reproducibility of the differential scanning calorimetry, DSC, provides an opportunity to study particularities of magnetic transition at Curie temperature, a phenomenon that at first glance is not related to heat flow measurements. Curie point of an amorphous alloy is very sensitive to development of relaxation and crystallization processes by annealing, so measuring of TC by DSC allows studying the kinetic parameters of these processes [35]. In particular, applicability and informativity of DSC for examination of structural transformations in the Finemet-type alloys are shown in [5, 6]. This method gives an opportunity to study the effect of magnetoelastic energy stored during the microwires fabrication on the TC and change of heat capacity of microwires. In present paper we carefully investigated the time-temperature dependences of the Curie temperature for Finemet-type glass coated microwires on annealing regimes in comparison to ribbon-shaped alloys. The goal of this research is to estimate the apparent values of activation energy of relaxation processes before crystallization as well as to study the change of heat capacity in the vicinity of TC.
107
EXPERIMENT Glass-coated Finemet-type microwires with alloy compositions Fe70.8Cu1Nb3.1Si13.5B9.6 and Fe73.8Cu1Nb3.1Si13B9.1 produced by the modified Taylor-Ulitovsky method [2] were taken for investigation. The microwires ha
