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We present an experimental and theoretical study of Pauli paramagnetism and martensite stabilization in a near equiatomic NiTi shape memory alloy. We demonstrate a direct correlation between strain-induced shear of the B19′ NiTi lattice and its electronic and thermodynamical features. An increase in the monoclinic angle β from 97.4 to 98° induces a 7% decrease in the magnetic susceptibility because of a shift and deepening of a dip in B19′ density of states at the Fermi level. It also produces a decrease in the B19′ enthalpy, which translates into an increase in the martensite-to-austenite transition temperature by 60 K. [ABSTRACT FROM AUTHOR]

Strain modulation during a two-way shape memory effect (TWSME) in a sputtered nitinol NiTi is used to reliably induce and switch by 90° a uniaxial magnetic anisotropy of a 20 nm thick Ni film during the thermal cycle from 300 K to 400 K. NiTi strain and its distribution are carefully measured by digital image correlation during tensile prestrain and subsequent temperature cycles in order to compare with Ni strain extracted from the magnetometry measurement and from transmission electron microscopy. In a NiTi/Ni bilayer, a variation of 2.7% strain in NiTi during the TWSME generates 1.3% strain in Ni, which results in a transition from −2 × 104 J/m3 in-plane magnetic anisotropy to +1 × 105 J/m3. Such a composite system offers a way to timely ease writability while maintaining high thermal stability at rest in magnetic media. [ABSTRACT FROM AUTHOR]

We report on the intercalation of a submonolayer of copper at 775 K underneath graphene epitaxially grown on Ir(111) studied by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at 77 K. Nucleation and growth dynamics of Cu below graphene have been investigated, and, most importantly, the intercalation mechanism has been identified. First, LEED patterns reveal the pseudomorphic growth of Cu on Ir under the topmost graphene layer resulting in a large Cu in-plane lattice parameter expansion of about 6% compared to Cu(111). Second, large-scale STM topographs as a function of Cu coverage show that Cu diffusion on Ir below graphene exhibits a low energy barrier resulting in Cu accumulation at Ir step edges. As a result, the graphene sheet undergoes a strong edges reshaping. Finally, atomicallyresolved STM images reveal a damaged graphene sheet at the atomic scale after metal intercalation. Point defects in graphene were shown to be carbon vacancies. According to these results, a Cu penetration path beneath graphene is proposed to occur via metal aided defect formation with no or poor self healing of the graphene sheet. This work illustrates the fact that Cu intercalation is harmful for graphene grown on Ir(111) at the atomic scale. [ABSTRACT FROM AUTHOR]