Spin-polarized Field Emission Research Articles

Fabrication and characterization of spin-polarized Co2MnGa field emission electron source

Spin-polarized electron emission from a Heusler alloy Co2MnGa field emitter was confirmed. The Co2MnGa tip was fabricated from Co2MnGa thin film epitaxially grown on MgO(100) substrate. An atomically clean surface of emitter apex was successfully obtained by field evaporation. It was confirmed that the (010) surface of the Co2MnGa emitter has a rather low work-function by the field emission characteristics from the clean surface. The spin-polarization of 66% was achieved from the field-emitted electrons around the (010) face at 42 K, which is in agreement with the theoretical results of the surface spin-polarization of Co2MnGa [J. Appl. Phys. 115, 113905 (2014)].

Spin-polarized field emission from Cr thin film deposited on W[formula omitted] tips

To generate high and stable spin-polarized electron beams by field-emission for applications to electron microscopy and spectroscopy, we demonstrated spin-polarized field-emitted electrons from a Cr thin film deposited on W〈001〉 tips at room temperature without an external magnetic field. A spin polarization of the field-emitted electrons of 35–50% was achieved when the Cr thickness was higher than 20 nm. In addition, a maximum spin polarization of 50% was achieved, consistent with the value for a Cr(0 0 1) surface expected by first-principles calculations. The polarization direction was also stable for 3 h with no abrupt change. This study indicates that antiferromagnetic Cr is proper cathode material for a field emitter than other ferromagnetic materials with an instability limited by superparamagnetic state.

Ferromagnetism at the summit: A perspective on: “Spin polarized field emission from Fe and co-coated W tips” by Y.R. Niu and M.S. Altman

Ferromagnetism at the summit: A perspective on: “Spin polarized field emission from Fe and co-coated W tips” by Y.R. Niu and M.S. Altman

Spin polarized field emission from Fe and Co-coated W tips

Spin polarized field emission from thin film Fe- and Co-coated W(001) and W(111) tips has been investigated. A transverse spin polarization component is detected in each case. For W(111) tips, the azimuthal orientation of polarization showed only a weak preference for the set of 〈1̅10〉 and 〈112̅〉 tip directions due to the competing influence of magnetocrystalline anisotropy and tip morphology on tip magnetization. On the contrary, the polarization direction for W(001) tips exhibited a strong preference for alignment with the transverse low-index crystallographic directions, i.e. the 〈110〉 for Co and 〈100〉 for Fe. Superparamagnetic fluctuations of the tip magnetization are evident in the polarization direction of emitted electrons when film coatings are very thin. At marginally larger thickness, long-term stability of the polarization magnitude and direction is observed at 300 K. A method for changing the stable spin polarization direction is also presented that exploits spontaneous flipping of the tip magnetization at elevated temperature.

Highly Spin-Polarized Field Emissions Induced by Quantum Size Effects in Ultrathin Films of Fe on W(001)

Spin-polarized field emissions from Fe pseudomorphic ultrathin films on W(001) surfaces are studied by density functional calculations. We found that nearly completely spin-polarized field emission currents can be realized in two and four Fe layers on W(001) and that these systems have the additional advantages of thermal stability and low work functions. The unusually high spin polarizations of the field emission current is traced to the Fe film's quantum size effects leading to spin-polarized quantum well states and surface resonance states.

Spin-polarized field emission from Ni(001) and Ni(111) surfaces

Spin-polarized field emission from Ni(001) and Ni(111) surfaces

Many-body and spin-dependent surface potential effects in spin-polarized field emission from metals

A spin-dependent generalization of the Appelbaum-Brinkman transfer-Hamiltonian method is used to develop a practical formalism for including many-body and spin-dependent surface-potential effects in the calculation of the field-emitted current from a ferromagnet. It is shown that this formalism reduces to that of Politzer and Cutler when many-body effects, the spin dependence of the surface potential, and the detailed position dependence of the surface potential are neglected. If, finally, the band structure is treated in the nearly-free-electron limit, the theory reduces to that of Chazalviel and Yafet.

Abstract: Electronic and magnetic properties of nickel as described using experimental spin-split energy band dispersions

Angle-resolved photoemission studies of Ni (111) and Ni (100) crystals, used to determine energy-vs-momentum s- and d-band dispersions, show that ferromagnetic nickel can be described by a spin-split itinerant band model with an exchange splitting. An experimental one-electron energy band model for Ni gives a consistent description of various electronic and magnetic properties including Fermi surface radii, spin-polarized field emission and photoemission data, Bohr magneton number and optical properties. (AIP)

Many-body and spin-dependent surface potential effects in spin-polarized field emission

Many-body and spin-dependent surface potential effects in spin-polarized field emission

Magnetism at surface and interfaces by spin-polarized field emission (Invited)

Magnetism at surface and interfaces by spin-polarized field emission (Invited)

Electron spin polarization in field emission from 3d-ferromagnets

We briefly discuss the present experimental and theoretical status of spin-polarized field emission studies.