Synthesis, Characterization, and Magnetoresistive Properties of the Epitaxial Pd0.96Fe0.04/VN/Pd0.92Fe0.08 Superconducting Spin-Valve Heterostructure

Abstract

A thin-film superconductor(S)/ferromagnet(F) F1/S/F2-type Pd0.96Fe0.04(20 nm)/VN(30 nm)/Pd0.92Fe0.08(12 nm) heteroepitaxial structure was synthesized on (001)-oriented single-crystal MgO substrate utilizing a combination of the reactive magnetron sputtering and the molecular-beam epitaxy techniques in ultrahigh vacuum conditions. The reference VN film, Pd0.96Fe0.04/VN, and VN/Pd0.92Fe0.08 bilayers were grown in one run with the target sample. In-situ low-energy electron diffraction and ex-situ X-ray diffraction investigations approved that all the Pd1−xFex and VN layers in the series grew epitaxial in a cube-on-cube mode. Electric resistance measurements demonstrated sharp transitions to the superconducting state with the critical temperature reducing gradually from 7.7 to 5.4 K in the sequence of the VN film, Pd0.96Fe0.04/VN, VN/Pd0.92Fe0.08, and Pd0.96Fe0.04/VN/Pd0.92Fe0.08 heterostructures due to the superconductor/ferromagnet proximity effect. Transition width increased in the same sequence from 21 to 40 mK. Magnetoresistance studies of the trilayer Pd0.96Fe0.04/VN/Pd0.92Fe0.08 sample revealed a superconducting spin-valve effect upon switching between the parallel and antiparallel magnetic configurations, and anomalies associated with the magnetic moment reversals of the ferromagnetic Pd0.92Fe0.08 and Pd0.96Fe0.04 alloy layers. The moderate critical temperature suppression and manifestations of superconducting spin-valve properties make this kind of material promising for superconducting spintronics applications.

Ab initio Investigation of Impurity Ferromagnetism in the Pd1−xFex Alloys: Concentration and Position Dependences

“…The current revival of interest is fueled by the potential use as a material of a choice for a weak and soft ferromagnet in superconducting Josephson magnetic random-access memory (MRAM) based on Josephson junctions [4][5][6][7][8][9][10][11][12][13]. The Pd-rich ferromagnetic Pd 1−x Fe x (0.01 < x < 0.1) alloy is used there in the form of a thin film fabricated utilizing magnetron sputtering [5][6][7][8][9][10][11][13][14][15], molecular-beam epitaxy (MBE) [15][16][17][18][19][20][21][22][23], and ion-beam implantation [24].…”

“…There is a scatter of opinions on the compositional and magnetic homogeneity of Pd 1−x Fe x films obtained by different deposition techniques: some papers report an indication of clustering [10,11,13,14] or formation of the nanograins of the Pd 3 Fe phase [15] in samples deposited with the magnetron sputtering technique; the others on MBE growth of thin Pd 1−x Fe x films [18][19][20][21][22][23] report on their high magnetic homogeneity; finally, the ionimplanted palladium films [24] show a significant influence of the Fe implant distribution on saturation magnetization (M s ) and Curie temperature (T C ) of the samples. It is not clear why and how the redistribution of iron solute in the Pd matrix influences M s and T C .…”

Controllable two- vs three-state magnetization switching in single-layer epitaxial Pd1-xFex films and epitaxial Pd0.92Fe0.08/Ag/Pd0.96Fe0.04 heterostructure

“…The experimental rotation of the magnetic moment by 90 degrees in epitaxial Pd1-xFex films has not been yet explored. In [18,19], based on magnetometry data, it was assumed that magnetization reversal occurs as a result of the coherent rotation of the magnetic moment by 180 degrees; and in the study of the Pd0.96Fe0.04/VN/Pd0.92Fe0.08 structure [23], stable parallel and antiparallel configurations of magnetic moments were obtained. However, the maximum amplitude of the triplet pairing component in the PdFe1/N/PdFe2 bilayer structure is achieved near the orthogonal magnetic configuration of the ferromagnetic layers PdFe1 and PdFe2 [6].…”

Ab initio investigation of impurity ferromagnetism in the Pd1-xFex alloys: concentration and position dependence

“…The current revival of interest has been fueled by a potential use as a material of a choice for a weak and soft ferromagnet in superconducting Josephson magnetic random-access memory (MRAM) based on Josephson junctions [4,5,6,7,8,9,10,11,12,13,14]. The Pd-rich ferromagnetic Pd 1−x Fe x (0.01 < x < 0.1) alloy is used there in a form of a thin film fabricated utilizing magnetron sputtering [5,6,7,8,9,10,11,12,14,15,16,17], molecular-beam epitaxy [16,17,18,19,20,21,22,23,24,25], and ion-beam implantation [26].…”

“…There is a scatter of opinions on compositional and magnetic homogeneity of Pd 1−x Fe x films obtained by different deposition techniques: some papers report on an indication of clustering [10,11,12,14,15] or formation of the nanograins of Pd 3 Fe phase [16,17] in samples deposited with the magnetron sputtering technique; the others on MBE growth of thin Pd 1−x Fe x films [20,21,22,23,24,25] report on their high magnetic homogeneity; finally, the ion-implanted palladium films [26] show a significant influence of the Fe implant distribution on saturation magnetization (M s ) and Curie temperature (T C ) of the samples. It is not clear why and how the redistribution of iron solute in the Pd matrix influences M s and T C .…”