Tunneling Evidence of Half-Metallic Ferromagnetism inLa0.7Ca0.3MnO3

Abstract

Direct experimental evidence of half-metallic density of states (DOS) is observed by scanning tunneling spectroscopy on ferromagnetic La 0.7 Ca 0.3 MnO 3 , which exhibits colossal magnetoresistance (CMR). Tunneling conductance data taken at 77 K, well below the Curie temperature T C ഠ 260 K, show close resemblance to the spin-split DOS spectrum calculated for the itinerant bands in the ferromagnetic state. The half-metallic spectral characteristics are absent in the paramagnetic state at room temperature, as well as in the undoped antiferromagnetic compound LaMnO 3 , which shows no CMR. These results directly implicate the half-metallic ferromagnetism in the phenomenon of CMR.

Finite-temperature spin polarization in half-metallic ferromagnets

“…There have been various arguments in favor of [27][28][29][30][31][32][33] and against 3,9,10,15-17 true half-metallic ferromagnetism. In our opinion, half-metallic ferromagnetism is an idealized limit, realistic only in perfect crystals at zero temperature.…”

Are half-metallic ferromagnets half metals? (invited)

“…Apart from a somewhat ambiguous scanning tunneling microscopy spectroscopy study undertaken at 77 K, 79 claims of 100% spin polarization at more elevated temperatures ͑Ͼ40 K͒ rest on evidence from spin-polarized photoemission [75][76][77] and spinpolarized inverse photoemission, 78 as summarized in Table I. Spin-resolved photoemission measurements [75][76][77] and spinpolarized inverse photoemission 78 that claim to provide evidence of half-metal behavior, in fact, do not.…”

Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganiteLa0.7Ca0.3MnO3Hughes1, Beyer2, Yeh3 2010Phys. Rev. BSelf Cite6020View full textAdd to dashboardCite

“…Although the occurrence of an energy gap in a nominally metallic manganite could not be explained by either band-structure calculations 10,11 or bulk electrical transport measurements, 21,22 the tunneling spectra of the metallic manganite over a wide energy range except near the Fermi level were actually consistent with theoretical calculations of the bulk electronic density of states. 17,18 Hence, it is reasonable to conjecture that the surface of manganites may be a thin layer with chemical compositions differing from those of the bulk. Thus, lower-bias ballistic electrons injected from the scanning tunneling microscopy ͑STM͒ tip could be more sensitive to the surface state, whereas ballistic electrons injected with higher bias could penetrate deeper into the bulk.…”

“…16 For instance, scanning tunneling spectroscopic ͑STS͒ studies of nominally metallic manganite epitaxial thin films [17][18][19][20] and single crystals 13 have always revealed either a small energy gap or a pseudogap ͑PG͒ near the Fermi surface. Although the occurrence of an energy gap in a nominally metallic manganite could not be explained by either band-structure calculations 10,11 or bulk electrical transport measurements, 21,22 the tunneling spectra of the metallic manganite over a wide energy range except near the Fermi level were actually consistent with theoretical calculations of the bulk electronic density of states.…”