Manipulation of magnetic anisotropy directions in spin valves deposited at oblique incidence.

Name: Alisson Carlos Kröhling
Type: PhD thesis
Publication date: 30/08/2019

Namesort descending Role
Edson Passamani Caetano Advisor *

Examining board:

Namesort descending Role
Antonio Alberto Ribeiro Fernandes External Examiner *
Edson Passamani Caetano Advisor *
Rubem Luis Sommer External Examiner *
Thiago Eduardo Pedreira Bueno Co advisor *
Valberto Pedruzzi Nascimento Internal Examiner *
Waldemar Augusto de Almeida Macedo External Examiner *

Summary: Using DC magnetron sputtering, with confocal magnetron configuration, an experimental method was developed to set controlled non-collinear anisotropy axes in ferromagnetic layers of Si(100)/Cu(8nm)/Py(10nm)/Cu(5nm)/Co(10nm)/IrMn(8nm)/ /Cu(3nm) morphologically modified spin valve heterostructures. The different morphologies were induced by keeping the sample holder: either (i) spinning, producing layers with random crystalline grains, or (ii) static, a condition WHERE the shadowing effect arises from the oblique angle incidence of the sputtered atoms, producing layers with columnar grains orientated in convenient directions. In this sense, Cu and Py layers were always deposited with in-phase columnar grain orientations, the Cu spacer layers were prepared either with out-of-plane columnar grain structures or in-plane random grains and the Co and IrMn layers columnar grains were orientated in different directions relative to the Py layer. Due to these columnar structures: (i) an artificial roughness emerged between the Py and Cu spacer layers and (ii) large uniaxial magnetic anisotropies, with pre-set directions, were stablished in the Py and Co layers. It was possible to establish the angle between the anisotropy axes directions of the Py and Co layers in a continuous interval from zero to 90°, resulting in a non-collinear magnetic coupling of structures. These types of artificial magnetic structures are not found in conventional spin valve devices with passive spacers in which the magnetic coupling is basically governed by bilinear and biquadratic spin interactions. The Co and Py interlayer magnetic couplings and the anisotropy axes directions of the ferromagnetic layers were strongly changed due to an artificial roughness induced by the misalignment of the layer’s columnar grains and/or due to the different Cu spacer morphology induced during the deposition. The different angles of the uniaxial anisotropies of the Py and Co layers as well as of the unidirectional anisotropy at the Co/IrMn interface are deeply dependent on the type of grain structures (columnar or random) and roughness of the Co/IrMn interface of spin valves. Magnetoresistance results are independent on Cu layer morphologies, producing a value of 2.5 % for 5 𝑛𝑚 thick Cu spacer. In brief, the methodology that we present here for spin valve preparation allows an extra control over the magnetism of the spin valve heterostructures, which can be promising for technological applications.
New studies, with thinner Cu spacer layer (or other metal) are required to show further applications of this type of spin-valve system.

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