Spin transport in epitaxial magnetic manganite/ruthenate heterostructures with an LaMnO 3 layer
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ONIC PROPERTIES OF SOLID
Spin Transport in Epitaxial Magnetic Manganite/Ruthenate Heterostructures with an LaMnO3 Layer A. M. Petrzhika*, G. A. Ovsyannikova,b, A. V. Shadrina,b, Yu. N. Khaidukovc, and L. Mustafac a
Kotel’nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow, 125009 Russia *email: [email protected] b Chalmers University of Technology, Department of Microtechnology and Nanoscience, Gothenburg, S41296 Sweden c MaxPlank Institute for Solid State Research, Stuttgart, 70569 Germany Received April 8, 2014
Abstract—Epitaxial La0.7Sr0.3MnO3/LaMnO3/SrRuO3 (LSMO/LMO/SRO) heterostructures with an LMO layer 0–35 nm thick are grown by laser ablation on an NdGaO3 substrate at a high temperature. Xray diffraction and transmission electron microscopy demonstrate sharp interfaces and epitaxial growth of the LSMO and SRO layers in the heterostructures at an LMO layer thickness of 0–35 nm. SQUID measurements of the magnetic moment of the heterostructures with an LMO layer and the data obtained with reflectometry of polarized neutrons show that the manganite LMO layer is a ferromagnet at a temperature below 150 K and strongly affects the magnetic moment of the heterostructures at low temperatures. The magnetoresistance of the mesostructure created from the heterostructure using lithography and ion etching decreases with increas ing LMO layer thickness and weakly depends on the direction of an applied magnetic field. If the LMP layer is absent, a negative magnetoresistance is detected; it is likely to be caused by a negative magnetization of the SRO layer. DOI: 10.1134/S1063776114100161
1. INTRODUCTION The tunnel junctions that consist of two ferromag netic electrodes separated by an insulator layer are of interest due to the possibility of creating nonequilib rium spin polarization of carriers and to a practical application in energyindependent magnetic memory [1]. A high tunneling magnetoresistance (TMR), which is required for practical application of such structures, appears when a weak applied magnetic field changes the magnetization direction in one or two of the electrodes. Using the Julliere model [2], we can write the magnetoresistance of the tunnel junction made of two ferromagnets that is induced by the trans port of spinpolarized carriers in the form [3, 4] 0
G sp = G sp [ 1 + P 1 P 2 cos ( β 1 – β 2 ) ]. 0 G sp
(1)
Here, is the conductivity of polarized spins, P1 and P2 are the spin polarizations, and angles β1 and β2 determine the magnetization directions in the ferro magnets. In the limiting cases of antiferromagnetic (antiparallel) and ferromagnetic (parallel) magnetiza tion directions, TMR is determined by the carrier polarization in the two ferromagnets, R AP – R P 2P 1 P 2 TMR = = (2) , 1 – P1 P2 RP where RAP and RP are the tunnel junction resistances for the antiparallel and parallel ordering, respectively. When the spin polarization directions of the two elec
trodes are opposite to each other, RP is hig
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