Magnetic and Magnetotransport Characteristics of Cr-Substituted Ni₅₅Mn₃₄Sn₁₁ Thin Films Grown by Magnetron Sputtering

Abstract

Highly oriented Cr-substituted Ni₅₅Mn₃₄Sn₁₁ Heusler thin films having thickness ~ 400 nm were deposited by Ultrahigh vacuum dc magnetron sputtering on MgO (100) substrates. At room temperature, the films exhibit a mixture of dominant L2₁ cubic austenite phase, as revealed by the intense (002) and (004) peaks, along with small fraction of the orthorhombic–martensitic phase. Surface morphology of the thin films showed distribution of Cr-rich and Cr-deficit regions together with patterned and aligned magnetic domains, thus bringing out the inherent room temperature ferromagnetism of the film. At temperatures above the Curie temperature, T_C ~ 321 K, the magnetic behaviour of the films is seen to follow the Curie law rather than the Curie–Weiss law. Ferromagnetic to antiferromagnetic transition appears at T_N ~ 247 K, which gives rise to exchange bias at low temperatures due to the coexistence of the two magnetic orders. This phase coexistence also leads to the formation of a spin glass state deep into the martensitic region. The film exhibits metal-like nature at high temperature and semiconductor-like behaviour with the lowering of temperature. A reentrant metallic state is observed at T ≤ 38 K during cooling that persists up to ≤ 62 K in warming cycle. The hysteresis in the ρ–T curve spread over a very wide temperature range confirms the magnetic phase coexistence in the martensitic state in the present thin films. The magnetoresistance (MR) first increases (2.4% at 300 K and H = 50 kOe) with temperature and maximizes to around ~ 3.25% at T = 150 K and then starts decreasing. Its value in the glassy state is very small. This shows that a magnetic liquid like state is more conducive to larger MR.