Magnetic properties of submicron Ni-Mn-Ga martensitic thin films
- PDF / 589,263 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 227 Views
W2.8.1
Magnetic properties of submicron Ni-Mn-Ga martensitic thin films M. Kohl, V.A. Chernenko, M. Ohtsuka1, H. Reuter2 and T. Takagi3 IMT, Forschungszentrum Karlsruhe, D-76021, Karlsruhe, Germany 1 IMRAM, Tohoku University, Sendai, 980-8577, Japan 2 IMF III, Forschungszentrum Karlsruhe, D-76021, Karlsruhe, Germany 3 IFS, Tohoku University, Sendai 980-8577, Japan ABSTRACT Two series of Ni-Mn-Ga thin films with two different compositions and various thicknesses in the submicron range are investigated with respect to their structural and magnetic properties. The films are fabricated by sputter deposition on alumina substrates and subsequent heat treatment. The martensitic transformation occurs well above room temperature showing a small thermal hysteresis width of about 6 K. The magnetic properties turn out to be thicknessdependent in the submicron range. In particular, in-plane magnetic susceptibilities increase and critical field strengths for onset of saturation decrease for decreasing thickness down to 0.1 µm by factors of 3–5 depending on the chemical composition. The Curie temperature TC decreases by about 25 K for samples with TC higher than the martensitic transformation. INTRODUCTION Ferromagnetic thermoelastic martensites formed as a result of a martensitic transformation in a ferromagnetic matrix represent a new type of material. Due to the coupling of the structural and magnetic degrees of freedom they exhibit extreme magneto-mechanical properties which open up new technical applications as sensors and actuators [1]. Concerning the development of novel devices for micro- and nano-applications, the development of thin film technology of such materials is of crucial importance. Recently, much effort has been undertaken to fabricate Ni-Mn-Ga films by sputtering technology [2–6]. For applications, the thin films should exhibit a perfectly reversible martensitic transformation with transformation temperatures well above room temperature. These conditions have already been met in previous work, e.g., on free-standing cantilever samples of 5 and 10 µm thickness demonstrating one-way and two-way shape memory behavior [2,4]. Based on these developments, Ni-Mn-Ga thin films have been successfully implemented in first prototypes of microactuators for optical applications [7]. Little information exists in the literature concerning the thermoelastic and magnetomechanical properties of thin films with submicron thickness [8]. In this paper, results on the structural behavior and magnetic properties of Ni-Mn-Ga thin films with different compositions and submicron thicknesses are presented. EXPERIMENTAL Two series of thin films (A and B) have been fabricated by radio-frequency (RF) magnetron sputtering using two different targets of nominal compositions Ni49.5Mn28.0Ga22.5 for thin films A and Ni52Mn24Ga24 for thin films B. Each series consists of five films with thicknesses ranging from 0.1 to 1 µm and a reference of 5 µm, which have been adjusted by the sputtering time. The deposition was performed at 200 W in a high-p
Data Loading...
