Functional properties of ni-mn-z (z= sn, in) heusler alloy ribbons and co-based metallic glasses

Abstract

ABSTRACT: In this work, besides characterizing the Magnetoimpedance effect in a set of Co-rich alloy ribbons at high frequencies, we have also studied the structural and the magnetic properties in Heusler alloy ribbons as well as their Magnetocaloric and Exchange-Bias effects. In order to reach the first aim, we have worked with near-zero magnetostriction amorphous alloy ribbons, which presented different magnetic behavior. The samples herein investigated have been Co66.5Fe3.5Si12.0B18.0 alloy ribbons with different width, Co69Fe4Si15B12 alloys ribbons with and without induced magnetic anisotropy by a field-quenched process, and Co66.3Fe3.7Si12.0B18.0 alloy ribbons with induced magnetic anisotropy by different stress annealing treatments. With the purpose of characterizing the samples magnetically, we have performed measurements of their hysteresis loops by inductive methods, along with the magnetoimpedance measurements. The results show that all the studied amorphous ribbons in the as-quenched state have a small transverse spontaneous anisotropy together with a small-negative magnetostriction coefficient, which imply a soft magnetic behavior in all of them. In addition, analyzing the magnetoimpedance response we have observed that all Co-based metallic-glasses studied in this work present a two-peaks behavior, being the MI effect highest in the ribbons with anisotropy induced by stress-annealing treatments. Likewise we have studied Ni-Mn-based Heusler alloy ribbons with the aim to understand some of their functional properties above mentioned. We have selected Ni45.5Mn43.0In11.5 and Ni50.0Mn37.0Sn13.0 as prototypes which undergo a martensitic transformation and exhibit the inverse magnetocaloric effect, according with the phase diagram of martensitic Ni-Mn-based Heusler alloys. A study of the annealing influence on the crystalline structure, magnetic and functional properties were carried out in Ni45.5Mn43.0In11.5 Heusler alloy ribbons. When the annealing temperature increases, the ordering degree and lattice parameters diminish. In addition, the grain size of the annealed ribbons increases in comparison with the as-quenched ones. After annealing treatments both martensitic transformation and inverse magnetocaloric effect are shifted towards high temperatures. Furthermore, in the low temperature range below 50 K, the coercive and exchange-bias fields increase as the annealing temperature rises. The magneto-structural transformation has been studied in the Ni50.0Mn37.0Sn13.0 Heusler alloy for both ribbon and rod shapes. In comparison with the ribbon shape, the temperature range of the martensitic transition is wider in the rod shape. However, the magnetization change between austenite and martensite phases is higher in the ribbon. Finally, magnetic measurements show a softer magnetic behavior in the martensite phase for the rod-shape than the ribbon one.