Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

Biswas, Chandan; Rawat, R.; Barman, S. R.

doi:10.1063/1.1925757

Cited by 145 publications

(109 citation statements)

References 23 publications

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“…This enhancement reflects Ni-d and Mn-d electronic contributions to the majority-spin density of states and is accompanied by significant reconstruction of the Fermi surface. Ni-Mn-Ga alloys with near-stoichiometric compositions, Ni 2 MnGa, are important functional materials [1] owing to their magnetic shape-memory [2], magnetocaloric [3] and magnetoresistive [4] properties. This ferromagnetic fcc L2 1 Heusler (a fcc = 5.81Å) was first identified by Webster et al [5] as a system undergoing a martensitic transition (MT) in its ferromagnetic phase (T C ∼ 380 K) with little magnetic hysteresis.…”

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confidence: 99%

Combined Experimental and Theoretical Investigation of the Premartensitic Transition inNi2MnGa

et al. 2008

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Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity and magnetic-moment measurements are reported for the magnetic shape-memory alloy Ni2MnGa over the temperature range 100 K < T < 250 K. All measurements detect clear signatures of the premartensitic transition (TPM ∼ 247 K) and the martensitic transition (TM ∼ 196 K). Temperature-dependent UPS shows a dramatic depletion of states (pseudogap) at TPM located 0.3 eV below the Fermi energy. First-principles electronic structure calculations show that the peak observed at 0.3 eV in the UPS spectra for T > TPM is due to the Ni-d minority-spin electrons. Below TM this peak disappears, resulting in an enhanced density of states at energies around 0.8 eV. This enhancement reflects Ni-d and Mn-d electronic contributions to the majority-spin density of states and is accompanied by significant reconstruction of the Fermi surface. [5] as a system undergoing a martensitic transition (MT) in its ferromagnetic phase (T C ∼ 380 K) with little magnetic hysteresis. In the last decade research on these alloys has focused on the structural and magnetic characterization and on their shape-memory applications [6]. First-principles calculations [7,8] and measurements on shape-memory alloys [9,10,11,12] indicate the driving role of the electronic structure and its relation to the lattice dynamics.The lattice dynamics of Ni 2 MnGa has been investigated from ultrasonic measurements [13] and neutron diffraction experiments [14,15,16]. It was found that the transverse TA 2 phonon branch exhibits pronounced softening at 1/3 of the zone boundary on decreasing the temperature, and this softening was described as a Bain distortion in the context of the Wechler, Lieberman, and Read theory of martensite formation [17]. In similar structural shape-memory alloys InTl [9], AuZn [10] and NiAl [11], this softening is associated with nesting features of the Fermi surface [8]. Below a certain temperature, there is a freezing of the displacements associated with this soft phonon so that a micro-modulated phase forms, which is described as a periodic distortion of the parent cubic phase [14]. In Ni 2 MnGa, the premartensitic phase develops with little or no thermal hysteresis and is driven by a magnetoelastic coupling [18]. On further cooling, Ni 2 MnGa transforms to an approximately fivelayered quasi-tetragonal martensitic structure. The lowtemperature phase is incommensurate [14] with a period (0.43,0.43,0) and exhibits well-defined phasons best characterized as charge-density wave (CDW) excitations [16].In this paper we study the role of conduction electrons in the two-step MT in Ni 2 MnGa using photoemission spectroscopy and thermodynamic measurements. LEED and X-ray diffraction Laue measurements show the quality of our sample is appropriate for high-resolution photoemission spectroscopy. Ultraviolet photoemission (UPS) measurements show the opening of a pseudogap at 0.3 eV below the Fermi energy at the MT and provide further evidence that the Fer...

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Combined Experimental and Theoretical Investigation of the Premartensitic Transition inNi2MnGa

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“…It is argued that the underlying mechanisms are mainly governed by the s-d scattering for the bulks and the spin transport for the thin films. 10,11 Among the Heusler alloys, Ni-Mn-Ga single crystals exhibit giant magnetic field-induced strains ͑MFISs͒ of ϳ6% ͑load-free͒ in the tetragonal martensitic phase and of ϳ10% in the orthorhombic martensitic phase as a result of the martensitic twin-variant reorientation induced by magnetic field, mechanical stress, and/or temperature. [13][14][15] This reorientation may also lead to a characteristic change in electrical resistivity due to crystallographic anisotropy.…”

Section: Introductionmentioning

confidence: 99%

“…5,6 More recently, the MR effect has been observed in some half-metallic Heusler alloys with the general formula Ni 2 Mn 1+x X 1−x ͑where X is a sp-element such as Sn, Sb, In, etc.͒ and in some Heusler-type ferromagnetic shape memory alloys ͑such as Ni-Mn-Ga alloys͒. [7][8][9][10][11][12] In particular, the reported MR effect in these Heusler alloys is basically in polycrystalline bulks and thin films with either positive or negative MR value, depending on applied magnetic field and ͑low͒ temperature. It is argued that the underlying mechanisms are mainly governed by the s-d scattering for the bulks and the spin transport for the thin films.…”

Section: Introductionmentioning

confidence: 99%

Twin-variant reorientation-induced large magnetoresistance effect in Ni50Mn29Ga21 single crystal

Zeng

Zhu

et al. 2010

Journal of Applied Physics

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Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars Appl. Phys. Lett. 99, 162508 (2011) Proper scaling of the anomalous Hall effect in the Co/Pt multilayers J. Appl. Phys. 110, 033921 (2011) Physical nature of anomalous peaks observed in extraordinary Hall effect measurement of exchange biased spin-valves with perpendicular anisotropy J. Appl. Phys. 110, 013913 (2011) Existence of modulated structure and negative magnetoresistance in Ga excess Ni-Mn-Ga Appl. Phys. Lett. 99, 021902 (2011) Thermoelectric properties of Ga-added CoSb3 based skutterudites J. Appl. Phys. 110, 013521 (2011) Additional information on J. Appl. Phys. We report a significant magnetoresistance ͑MR͒ effect arisen from magnetic field-induced reorientation of martensitic twin variants in a ferromagnetic shape memory Ni 50 Mn 29 Ga 21 single crystal. The measured electrical resistivity shows large anisotropy and the measured MR value is as large as 25% over the wide temperature range of 230-315 K at a moderate magnetic field of 1.2 T. It is found that a proper combination of the initial state of martensitic twin variants and the direction and magnitude of applied magnetic field can give rise to either positive or negative MR value of ϳ25%, thus allowing a periodic modulation of the MR effect in response to varying the spatial angle between the directions of applied magnetic field and electric current for every 180°.

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“…This magnetically controlled resistivity/resistance ͓referenced as magnetoresistance ͑MR͒ effect͔ shows a potential application in novel magnetic memory storage device. 11 Current study on the MR effect of Ni-Mn-Ga alloy have been mostly carried out in polycrystalline system, [12][13][14] where MR effect can be understood by spin transport mechanism that considered different magnetization processes in large ferromagnetic clusters and spin reorientation of small clusters and boundary spins. However, the study on the electrical resistivity in different single-variant state is rarely reported in experimental observation and theoretical calculation.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy of the electrical transport properties in a Ni2MnGa single crystal: Experiment and theory

Zeng

Cai

et al. 2010

Journal of Applied Physics

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Electrical transport properties in ferromagnetic shape memory Ni-Mn-Ga single crystal have been investigated both in experiment and theory by analyzing electrical resistivity along different crystallographic directions during heating. The experimental results show a clear first-order martensitic transformation and a large anisotropic resistivity ͑AR͒ of 23.7% at the tetragonal martensitic phase. The theoretical conductivity ͑ =1/ ͒, estimated using first-principles calculations combined with classical Boltzman transport theory, proves essential crystallographic anisotropic resistivity ͑AR= 31%͒ in the martensitic phase and agrees well with experimental results. The AR in the martensitic phase is reveled to mainly originate from the splitting of the minority-spin Ni 3d and Ga 4p states near the Fermi level and hence reconstruction of the minority-spin Fermi surface upon martensitic transformation.

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Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

Cited by 145 publications

References 23 publications

Combined Experimental and Theoretical Investigation of the Premartensitic Transition inNi2MnGa

Combined Experimental and Theoretical Investigation of the Premartensitic Transition inNi2MnGa

Twin-variant reorientation-induced large magnetoresistance effect in Ni50Mn29Ga21 single crystal

Anisotropy of the electrical transport properties in a Ni2MnGa single crystal: Experiment and theory

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