Insulating magnetic oxides for spintronic applications
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Abstract
Current technologies for data storage and information processing are heavily reliant on
metallic, ferromagnetic materials. This hinders further improvement of devices due
to a sensitivity to external perturbations, limits of processing speeds and excessive
Joule heating from the passing charge currents.
In this thesis, several promising
material composites are explored for implementing magnonic logic operations. On
a more fundamental side, interfacial effects are employed for probing the magnetic
anisotropies and phase changes of a novel material system.
Spin currents are discussed as an information carrier and for information processing.
In magnetically ordered insulators, these spin currents are carried by magnons, the
quanta of spin waves. The ferrimagnetic insulator Y3Fe5O12 (YIG) has shown to be
able to transport magnons over large distances. However, for building devices based
on magnons to implement key logic operations, one needs the possibility to actively
manipulate the spin current. To this end, this thesis considers the experimental im-
plementation of a magnon valve using bilayers of YIG and another magnetic garnet,
Gd3Fe5O12.
An alternative approach to implement improvements to spintronic devices is to replace
the ferromagnetic material with an antiferromagnet, enabling writing speeds in the
terahertz range. However, determining the state of an antiferromagnet is a major
challenge necessitating the development of new techniques. One of these is spin Hall
magnetoresistance (SMR), a surface-sensitive all-electrical measurement that probes
the magnetic order of a material. In this thesis, SMR is utilized to probe the magnetic
properties of the antiferromagnetically ordered compound TmFeO3 (TFO). First, a
single crystal of TFO is investigated and its structural and magnetic properties are
determined using bulk measurements. Using then only surface-sensitive SMR, we can
attribute the electrical signals to the magnetic properties of the TFO.
However, for device applications, bulk materials are not suitable. This motivates us
to grow TFO as thin films, using pulsed laser deposition. The dependence of the mag-
netic properties on the choice of substrate is demonstrated. These thin films possess
similar properties to single crystals, as probed with volume-sensitive measurements.
Performing then surface sensitive SMR measurements on these samples allows us to
probe the magnetic properties of the TFO thin film in a more device relevant setting.