Wydarzenia

Seminarium Międzynarodowego Laboratorium Silnych Pól Magnetycznych i Niskich Temperatur PAN

Development of new materials based on Heusler alloys with increased functional properties for application in micromechan-ical devices and alternative

Elvina T. Dilmieva

International Laboratory of High Magnetic Fields and Low Temperatures

Great fundamental and practical interest is the study of functional materials, which change their shape and size under the influence of external factors (the magnetic field or the ambient temperature) and has magnetocaloric effect. These materials are promising for alternative energy and micro- and nanomechanics and many other fields.

Heusler alloys are ferromagnetic with shape memory effect. These materials have a thermoelastic martensitic transition into the ferromagnetic phase of the alloy, that is at a temperature below Curie point. Well enough studied representativeof these alloys is a Ni-Mn-Ga Heusler alloy, which can change its shape and size under the influence of an external magnetic field at a constant temperature. This characteristic can be extremely useful for applications in micromechanics, such as creating tweezers for manipulating single living cell at a constant temperature. The main limiting factor, which does not allow implement such alloys in technique today, is very large value of the external magnetic field required for the implementation of reversible thermoelastic martensitic structural transition. For the Ni-Mn-Ga alloys, the minimum value of this field is about 8T. In this connection, an active search is other Heusler alloys, in which a giant deformation induced by the magnetic field will be reached in the secondary field (about 2T).

The most interesting results were obtained in studies of non-stoichiometric alloys of Ni-Mn-In-X, where X - transition metal. In these alloys, there is an unusual combination of phase transformations. This is a structural transition from the ferromagnetic to the antiferromagnetic state. Such transitions are called meta-magnetostructural. The properties of alloys Ni-Mn-In-X strongly dependent on the composition. The sensitivity of the martensitic transition temperature to the magnetic field in some formulations it may reach 14 K/T. These data indicate on the perspective to the search of compounds of Ni-Mn-In-X Heusler alloys, which will be the basis for magnetically micromechanical devices.

Another promising area of application of Heusler alloys is alternative energy. In recent years, a large number of works devoted to the study of the magnetocaloric effect (MCE) in these and other intermetallic compounds. MCE is maximum near the magnetic phase and magnetostructural transitions. But the main problem is irreversible and the small value of the the MCE. It is proposed by further heat treatment will reduce the irreversibility of the effect.

There are several difficulties for solution of these applications. The main is to find an alloy with excellent functional properties on the condition that even a small change in the composition of three, four and five component Heusler alloy is a sharp change in temperatures of phase transformations and their associated effects. The present work is devoted to the development of new functional metamagnetic family of Heusler alloys Ni-Mn-X (In, Co, Ga), the study of their physical and functional properties