X-ray absorption study of the ferromagnetic Cu moment at theYBa2Cu3O7/La2/3Ca1

Abstract

With x-ray absorption spectroscopy and polarized neutron reflectometry we studied how the magnetic proximity effect at the interface between the cuprate high-T C superconductor YBa 2 Cu 3 O 7 (YBCO) and the ferromagnet La 2/3 Ca 1/3 MnO 3 (LCMO) is related to the electronic and magnetic properties of the LCMO layers. In particular, we explored how the magnitude of the ferromagnetic Cu moment on the YBCO side depends on the strength of the antiferromagnetic (AF) exchange coupling with the Mn moment on the LCMO side. We found that the Cu moment remains sizable if the AF coupling with the Mn moments is strongly reduced or even entirely suppressed. The ferromagnetic order of the Cu moments thus seems to be intrinsic to the interfacial CuO 2 planes and related to a weakly ferromagnetic intraplanar exchange interaction. The latter is discussed in terms of the partial occupation of the Cu 3d 3z 2 −r 2 orbitals, which occurs in the context of the so-called orbital reconstruction of the interfacial Cu ions.

Granular superconductivity and charge/orbital order in YBa2Cu3O7 /manganite trilayers

“…This leads to a redistribution of the holes on the Cu ions from the d x 2 −y 2 orbital (where they reside in bulk cuprates) toward the d z 2 −r 2 orbital. Along with this orbital reconstruction comes an induced ferromagnetic moment of the interfacial Cu ions that aligns antiparallel to the Mn moment [24,33]. Nevertheless, the superconducting response of these YBCO/LCMO multilayers is only moderately affected by the exchange coupling to the ferromagnetic Mn moments and the induced Cu moments, and a reasonably sharp SC transition with T c > 60 K can be realized, as long as the YBCO layer consists of at least four monolayers [20,28,31].…”

“…An additional platform for testing and controlling the competition between different orders has emerged from the progress in growing heterostructures based on thin active layers of these complex oxides with well-defined and atomically sharp interfaces [4,[11][12][13]. A well-studied example are multilayers comprised of the cuprate high-T c superconductor YBa 2 CuO 7 (YBCO), with a bulk critical temperature T c ≈ 90 K, and the CMR manganites La 2/3 Ca 1/3 MnO 3 (LCMO) and La 2/3 Sr 1/3 MnO 3 (LSMO) with bulk ferromagnetic transition temperatures T Curie ≈ 270 and 330 K, respectively, and saturation moment of about 3.7 μ B per Mn ion [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. The focus of the initial work on these multilayers was on the competition between the antagonistic superconducting and ferromagnetic orders and was motivated by the progress with superconductor/ferromagnet heterostructures based on conventional superconductors, like Nb, Pb, or Al, and conventional ferromagnets, like Gd, Fe, Co, Ni, or permalloy.…”

“…In comparison, the research on the cuprate/manganite multilayers is less advanced and still aimed at developing a better understanding of the basic phenomena that occur at these interfaces. Crucially, an electron transfer across the interface, from the manganite to the YBCO layer, and an orbital reconstruction of the interfacial Cu ions have been identified [24,25,33]. The latter originates from a strong covalent bonding between the interfacial Cu and Mn ions via the apical oxygen.…”

Controlling the strength of ferromagnetic order in YBa2Cu3O7/LaPrada1, Gaina2, Biškup3 et al. 2019Phys. Rev. BSelf Cite14050View full textAdd to dashboardCite

“…On the one hand, in superlattices made from YBCO and LCMO layers with small individual layer thicknesses of about 10 nm, it was shown that the "dead layer" can be as thin as a single or two LCMO unit cells. The suppression of the ferromagnetic moment is incomplete here, and there is even a weak ferromagnetic moment induced on the YBCO side [26][27][28][29]. The average ferromagnetic moment of the thin LCMO layers can exceed 3 μ B /Mn ion, and the Curie temperature can be as high as 220-230 K [20,30].…”

Magneto-transport in La2/3Sr1/3MnO3/YBa2Cu3O7/Alq3/Co spin-valves

“…[20][21][22][23]. Moreover, there is evidence for a strong hybridisation of the interfacial Cu and Mn ions (along the interfacial Cu-O apical -Mn bonds) which gives rise to an orbital reconstruction of the interfacial Cu ions and an antiferromagnetic exchange interaction that can also induce Cu moments [22][23][24] that are, however, likely bound to the interface. To our best knowledge there exists no direct measurement of the spin-polarization of the charge carriers at the cuprate/manganite interface and the length scale over which it persists away from the interface.…”