Positron annihilation study of the Fermi surface of Ni<sub>2</sub>MnGa

Haynes, T. D.; Watts, RJ; Laverock, J.; Major, Zs.; Alam, M. A.; Taylor, J. W.; Duffy, J. A.; Dugdale, Stephen B

doi:10.1088/1367-2630/14/3/035020

Cited by 44 publications

(47 citation statements)

References 66 publications

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“…The observation of a phase mode in the 10M phase [14] also suggested the electronic instability. In fact, the electronic band structure studies [11,15,16] revealed the possible Fermi surface nesting conditions for all of the observed structural modulations. However, for the case of the 14M martensite, it was argued that the modulated phase can be constructed from nonmodulated martensitic unit cells [17,18].…”

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confidence: 91%

“…While the data on the evolution of the Fermi surface with doping are unavailable, there are numerous observations that support such a scenario. First of all, calculations of the static electronic susceptibility [15] suggest the contributions from the majority and minority spin are considerably different [16]. Since doping with Co is found to strongly affect both the total magnetic moment [32][33][34] as well as densities of states in the minority-and majority-spin channels [20,32], it is likely that the peak in the static electronic susceptibility is pushed from q max ð 4 7 ; 4 7 ; 0Þ towards the next major commensurability wave vector q max ð 1 2 ; 1 2 ; 0Þ.…”

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confidence: 99%

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Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

et al. 2015

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The origin of the martensitic transition in the magnetic shape memory alloy Ni-Mn-Ga has been widely discussed. While several studies suggest it is electronically driven, the adaptive martensite model reproduced the peculiar nonharmonic lattice modulation. We used femtosecond spectroscopy to probe the temperature and doping dependence of collective modes, and scanning tunneling microscopy revealed the corresponding static modulations. We show that the martensitic phase can be described by a complex charge-density wave tuned by magnetic ordering and strong electron-lattice coupling. DOI: 10.1103/PhysRevLett.115.076402 PACS numbers: 71.45.Lr, 78.47.-p, 81.30.Kf, 81.70.Fy Magnetic shape memory alloys present a new type of multifunctional materials, which display strong coupling between the magnetic and structural degrees of freedom. The ferromagnetic Ni-Mn-Ga alloy serves as a prototype system, displaying a giant 12% magnetic-field-induced strain in its low-temperature (T) martensitic phase (M phase) [1,2]. Since in Ni-Mn-Ga the M-phase transition can be tuned far above the room temperature by changing stoichiometry or doping [3,4], this alloy is of special technological interest [1,2,5].The rich phase diagram of Ni 2þxþy Mn 1−x Ga 1−y is characterized by a complex sequence of phase transitions. In its high-T (austenite) phase, Ni-Mn-Ga has a cubic L2 1 Heusler structure. At the M-phase transition temperature T M , the lattice undergoes a transformation, which can be described by a periodic shuffling of (011) planes along the ½011 direction [6]. Depending on the stoichiometry and the residual stress, the resulting low-T M phase is commonly found to have either tetragonal or orthorhombic symmetry, with a modulation period of ten (10M) or 14 (14M) atomic layers [6,7], respectively. For specific stoichiometries, e.g., Ni 2þx Mn 1−x Ga with x ≲ 0.1, a premartensitic phase (PM phase) is observed above T M [3] with the transition temperature T PM up to 50 K above T M [3,8]. In the PM phase, the lattice displays a harmonic threefold modulation with the wave vector q PM ¼ q max ð 1 3 ; 1 3 ; 0Þ. Inelastic neutron scattering studies of the high-T cubic phase [9] showed a dramatic softening of the TA-2 phonon branch at q PM , indicative of a Kohn anomaly. These observations [9][10][11][12], together with the observed opening of a pseudogap at T PM [8,13], suggest an electronic instability within the Peierls scenario to be driving the PM-phase transition. The observation of a phase mode in the 10M phase [14] also suggested the electronic instability. In fact, the electronic band structure studies [11,15,16] revealed the possible Fermi surface nesting conditions for all of the observed structural modulations. However, for the case of the 14M martensite, it was argued that the modulated phase can be constructed from nonmodulated martensitic unit cells [17,18]. This adaptive martensite scenario [17][18][19] recently received considerable attention.To determine which theory gives a more appropriate physical picture of the pha...

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Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

et al. 2015

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“…For example, the 2D-Angular Correlation of Annihilated Radiation (2D-ACAR) measurement to determine fragile Fermi surface pieces of complex materials is source limited and may require several months of data accumulation. 6,7 As demonstrated in 8 , the Positron Annihilation induced Auger Electron Spectroscopy (PAES) 9 measurement time has been significantly improved with the availability of an intense source. Electron-positron plasma, 10,11 Positronium (Ps) Bose-Einstein Condensate (BEC), 12 Ps 2 molecule formation, 13 and gamma-ray laser 14 experiments are also among the many requiring high-intensity positron sources.…”

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confidence: 99%

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

Golge

Vlahović

Wojtsekhowski

2014

Journal of Applied Physics

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We present a conceptual design for a novel continuous wave electron-linac based high-intensity high-brightness slow-positron production source with a projected intensity on the order of 10 10 e + /s. Reaching this intensity in our design relies on the transport of positrons (T + below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. This design progressed through Monte Carlo optimizations of: electron/positron beam energies and converter target thickness, transport of the e + beam from the converter to the moderator, extraction of the e + beam from the magnetic channel, a synchronized raster system, and moderator efficiency calculations. For the extraction of e + from the magnetic channel, a magnetic field terminator plug prototype has been built and experimental results on the effectiveness of the prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.

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“…A positron annihilation study by Haynes et al 104 has helped to clarify the Fermi surface topology. Haynes et al were able to make a full three-dimensional reconstruction of the Fermi surface at 300 K from six measured projections.…”

Section: Ni 2 Mngamentioning

confidence: 99%

Probing the Fermi surface by positron annihilation and Compton scattering

Dugdale

2014

Low Temperature Physics

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Positron annihilation study of the Fermi surface of Ni₂MnGa

Cited by 44 publications

References 66 publications

Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

Probing the Fermi surface by positron annihilation and Compton scattering

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Positron annihilation study of the Fermi surface of Ni2MnGa

Cited by 44 publications

References 66 publications

Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

Probing the Fermi surface by positron annihilation and Compton scattering

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Positron annihilation study of the Fermi surface of Ni₂MnGa