Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)

Abstract

Materials with spin-polarized charge carriers are the most demanded in the spin-electronics. Particularly requested are the so-called half-metals which have the maximum attainable value of carrier spin polarization. Doped manganites are in the list of compounds with, potentially, half-metallic properties. The point-contact (PC) Andreevreflection (AR) spectroscopy is a robust and direct method to measure the degree of current spin polarization. In this report, advances in PCAR spectroscopy of ferromagnetic manganites are reviewed. The experimental results obtained on "classic" s-wave superconductor -ferromagnetic manganites PCs, as well as related theoretical models applied to deduce the actual value of charge carrier spin-polarization, are discussed. Data obtained on "proximity affected" contacts is also outlined. Systematic and repeatable nature of a number of principal experimental facts detected in the AR spectrum of proximity affected contacts suggests that some new physical phenomena have been documented here. Different models of current flow through a superconductor-half-metal ferromagnet interface, as well as possibility of unconventional superconducting proximity effect, have been discussed. PACS

Transport Properties of La0.7Sr0.3MnO3/MgB2 Random Nanocomposites

“…[8][9][10][11]. Long-range proximity effect and induced superconducting order in such hmF as manganites was detected, in particular, by Andreev reflection in experiments on the manganite-S point contacts [12][13][14][15] (manganite = La 0.7 Ca 0.3 MnO 3 , La 0.7 Sr 0.3 MnO 3 , S = Pb, Nb, MgB 2 ). In addition to the spectroscopic manifestation of the proximity effect in contacts of an S with manganites, a superconducting current has been detected in numerous studies of hybrid S-manganite-S film's structures [8][9][10][11]16].…”

Low-Temperature Intergranular Spin Transport in $${\mathbf {La_{0.5}Ca_{0.4}Li_{0.1}MnO_3}}$$ La 0.5 Ca 0.4 Li 0.1 MnO 3 Manganite Under High Magnetic Field $$\mathbf {(1\,T\le H \le 14\,T)}$$ ( 1 T ≤ H ≤ 14 T )

“…The SPT mechanism in manganites under weak magnetic fields is studied extensively [1][2][3][4][5][6][7][8], while the SPT at high fields are found to be out of due attention [7,9]. On the other hand, the interpretation of physical mechanisms for a low-temperature minimum (LTM) of resistivity occurring in manganites still remains in question and no consensus exists on the nature of this phenomenon [10][11][12][13][14][15][16][17][18][19][20][21][22].…”

“…The spin-polarized transport phenomena (SPT) in manganites have attracted extensive attention in recent years [1][2][3] that is triggered by practical applicability of manganites (e.g., in manufacturing of spintronics elements). The SPT mechanism in manganites under weak magnetic fields is studied extensively [1][2][3][4][5][6][7][8], while the SPT at high fields are found to be out of due attention [7,9].…”

Dependence of Andreev reflection and Schottky barriers on GaMnAs/Nb interface treatment

“…2,3 This technique has been successfully used to extract the spin polarization in many ferromagnetic materials, where the analysis typically uses a modified BTK model to account for the reduced minority spin densities. [4][5][6] The analysis of AR data is not straight forward, since several factors have to be taken into account, like the z-factor, the temperature, and the spin scattering, in addition to the spin polarization. 7 Recent papers have also pointed out to the significant effect of the spin-independent resistance contribution from the bulk of the ferromagnetic film and the spreading resistance.…”