In the last 30 years the magnetic data storage industry has enjoyed a steady increase in the storage density, from about 10 Mb/in2 in the early 90’s to the present ~1.0 Tb/in2 - a hundred thousand fold increase. Such progress has been driven by the large customers’ demand for cheap and reliable data storage capacity, which is certainly due to increase at an unprecedented speed in the next few decades. Recent estimates suggest that the worldwide data production in 2025 will reach 22 zettabytes, i.e 22 trillion gigabytes. In fact, nearly any modern human activity requires storing information.
Magnetic data storage is currently the only technology capable of addressing such massive and constantly growing volumes of data, but it faces the problem of shrinking magnetic memory units from the micro to the nano-scale. The ultimate limit for data storage is the atomic one, where every atom magnetic moment can store a single (or multiple) bits. Additionally magnetic atoms have been also proposed as a platforms for quantum computing. The question then becomes how to address and control these magnetic moments.
The only reliable way to probe and switch the magnetism at the atomic level is through an electrical current. In fact typical experiments involve reading the conductance of nano-junctions. Understanding in detail the fine features of these experiments and, even more ambitiously, model these without relying on adjustable parameters is a formidable theoretical challenge. Firstly one has to solve an intrinsic many-body problem. Secondly, this is an electron transport problem and one needs a non-equilibrium description. Finally, the fine details of the system electronic structure play an important role.
The main questions addressed by SpinMan were:
Can one construct a material-specific parameter-free many-body scheme, applicable to real nano-junctions?
Then, can we describe and moreover predict whether and how a magnetic moment can be addressed and controlled at the atomic scale through an electrical current?
Ultimately we achieved these objectives. We indeed developed a many-body method for electron transport through nano-scale systems, which is fully predictive.
The method was applied to gain a deep and general understanding about the interaction of a charge current with magnetic nano-systems across a variety of experimental relevant situations. While in the past the theoretical modelling of such systems had been limited to fitting the parameters of effective models, we were able to relate the macroscopic quantities accessible to measurements to a first-principles atomic level understanding of the physics. Finally, by working in collaboration with the experimental group of Prof. Sebastian Loth (University of Stuttgart, Germany), we discovered that measuring the dynamics of a few-atom magnetic system permitted it to function as a highly sensitive surface-integrated sensor capable of detecting the presence and state of nearby magnetic nano-objects. The ability to sense the magnetic state of individual magnetic nano-objects is a key capability for powerful applications such as the measurement of magnetism in complex structures with nanometer precision.
