Periodic Co/Nb pseudo spin valve for cryogenic memory

Abstract

We present a study of magnetic structures with controllable effective exchange energy for Josephson switches and memory applications. As a basis for a weak link we propose to use a periodic structure composed of ferromagnetic (F) layers spaced by thin superconductors (s). Our calculations based on the Usadel equations show that switching from parallel (P) to antiparallel (AP) alignment of neighboring F layers can lead to a significant enhancement of the critical current through the junction. To control the magnetic alignment we propose to use a periodic system whose unit cell is a pseudo spin valve of structure F1/s/F2/s where F1 and F2 are two magnetic layers having different coercive fields. In order to check the feasibility of controllable switching between AP and P states through the whole periodic structure, we prepared a superlattice [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)]6 between two superconducting layers of Nb(25 nm). Neutron scattering and magnetometry data showed that parallel and antiparallel alignment can be controlled with a magnetic field of only several tens of Oersted.

Controlling the proximity effect in a Co/Nb multilayer: the properties of electronic transport

“…where l is the length of the strip, W and d are the width and the thickness of the multilayer structure, respectively. It can be concluded that small changes in the temperature or in the applied magnetic field [ 9 ] can significantly change (from zero to relatively large values) the kinetic inductance of thin s-layers in the hybrid structures studied in this work.…”

“…The next step was to experimentally verify the significant changes, predicted in the model, for the pair potential in thin s-layers of a [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)] 3 AFM. For these superlattices, the possibility of switching between the P and AP cases, using a magnetic field with an intensity of ≈30 oersteds, has already been demonstrated [ 9 ]. The samples were prepared by using the magnetron sputtering system Leybold Heraeus Z-400 during a single deposition cycle without depressurization of the chamber.…”

“…Switching from the antiparallel (AP) to the parallel (P) alignment of neighboring F1 and F2 layers leads to a significant enhancement of the effective exchange field in this artificial ferromagnet. Previously, the properties of [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)] 6 multilayer structures for cryogenic memory applications were studied using polarized neutron scattering and magnetometry techniques [ 9 ]. In particular, the parameter regions where the aforementioned switching between the P and AP orientations of the F1 and F2 layers is possible were found experimentally.…”

The simulation of processes for forming a superconductor spin valve based on the “superconductor-ferromagnetic” nanostructure

“…Кроме того, в реальных материалах граница контактного слоя является достаточно протяженной и структурно неоднородной. Магнитные свойства конечного материала находятся в прямой зависимости от нанометровых магнитных кластеров и ферромагнитных доменов в зоне контакта, а также их взаимодействия между собой [21]. В связи с вышесказанным, актуальна задача детального исследования структуры контактного слоя слоистых материалов сверхпроводник-ферромагнетик и определения его пространственного профиля.…”

“…В связи с вышесказанным, актуальна задача детального исследования структуры контактного слоя слоистых материалов сверхпроводник-ферромагнетик и определения его пространственного профиля. Для построения методологических основ и проведения теоретических исследований структуры многослойных спиновых систем в данной работе смоделирована наносистема с управляемой эффективной энергией обмена для устройств памяти и переключателей типа «спиновый вентиль» [22,23], представляющая собой многослойную структуру, состоящую из ферромагнитных нанопленок кобальта, которые разделены тонкими слоями сверхпроводника ниобия.…”