MAGNETORESISTANCE OF Ni-Mn-Ga THIN FILMS IN THE VICINITY OF MAGNETOSTRUCTURAL TRANSFORMATION

Mykola M. Krupa 1Volodymyr A. Chernenko 1Igor V. Lezhnenko 1Makoto Ohtsuka 2Yurii B. Skyrta 1Manfred Kohl 3

1. Institute of Magnetism, N.A.S. of Ukraine, 36-b Vernadsky Blvd, Kyiv 252142, Ukraine
2. Tohoku University, Sendai, Japan
3. Forschungszentrum Karlsruhe, IMT, Postfach 3640, Karlsruhe 76021, Germany

Abstract

The enhanced sensitivity of the martensitic transformation (MT) temperature on the magnetic field has been already reported for the Ni-Mn-Ga alloys transforming near Curie temperature. The manyfold increase of the value of resistivity anomaly at MT as a function increasing MT temperature in Ni-Mn-Ga alloys is also a common knowledge.

Aforementioned behavior gave us motivation to study a magnetic field influence on the resistivity anomaly near magnetostructural transformation exhibited by the Ni-Mn-Ga thin films.

Magnetron deposition and Ni52Mn24Ga24 and Ni49.5Mn28Ga22.5 targets have been used to produce as-deposited Ni-Mn-Ga thin films with the thickness ranging from 0.1 to 5 microns. The substrate temperature was kept about 320 K. Annealing of thin films was made in vacuum at 1273K for 1h. X-ray diffraction and optical microscopy were used for the structural characterization of the films. The temperature dependences of resistivity in the range of 293-373 K under in-plane and out-of-plane magnetic field up to 1.2 T were studied. A reversible hysteretic MT in the temperature interval of 350-370 K was observed. In the temperature region outside of this interval the magnetoresistance is small while in the temperature interval in which MT occurs the maximum of magnetoresistance is observed whose value reaches 6 % in magnetic field of 1.2Т. An analysis of the electrical, structural and magnetic properties of investigated films offers the mechanism explaining anomalous behaviour of the magnetoresistance near MT in Ni-Mn-Ga thin films.

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Presentation: poster at E-MRS Fall Meeting 2005, Symposium C, by Mykola M. Krupa
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-20 13:55
Revised:   2009-06-07 00:44
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