Magnetic Domain Walls and Macroscopic Magnetization-Related Elastic and Anelastic Effects during Premartensitic Transition in Ni2MnGa

Abstract

The temperature and field dependences of internal friction and Young’s modulus are studied using a high-resolution ultrasonic (90 kHz) technique in stoichiometric ferromagnetic Ni2MnGa shape memory alloy close to the premartensitic transformation temperature, TPM, in the demagnetized state and under moderate fields. Several new effects observed like an apparent Young´s modulus softening close to TPM under moderate fields, instead of the hardening outside this range, as well as existing controversies in the apparent elastic and anelastic properties of Ni2MnGa close to TPM are explained by microeddy and macroeddy current relaxations that to date have been disregarded.

Effect of Acoustic Oscillations on Non-Equilibrium State of Magnetic Domain Structure in Cubic Ni2MnGa Single Crystal

“…Samples of nearly stoichiometric Ni 2 MnGa were prepared from the same single crystal as used in Refs. [ 24 , 25 ]. The crystal was produced at Adaptamat Ltd., Helsinki, Finland, annealed at 1300 K for 96 h and slowly cooled at 50 K/h.…”

“…The samples oriented along [100] axis were spark cut and chemically polished. The temperatures of phase transformations were determined using ac impedance measurements: the Curie temperature T C = 383 K, the pretransformation temperature T PM = 261 K, the martensitic transformation start temperature M s = 201 K [ 25 ]. Data on magnetization and magnetic domain structure were reported in Supplement 2 of Ref.…”

“…This gap is essentially filled in Refs. [ 24 , 25 ]. In the present work we show that classical treatment of the magnetomechanical IF perfectly accounts for rather peculiar magnetoelastic effects in cubic Ni 2 MnGa.…”