Synopsis

This website aims to disseminate, and encourage fast-paced, academic/industrial research on, a concept to harvest energy due to magnetic fluctuations (see below). Depending on the magnetic object considered, harvesting these fluctuations can be accomplished using spintronics, an industrially mature next-generation technology for ultra-low power information storage and computing. Several implementations in which the magnetic fluctuator exploits paramagnetism have been reported. Among them is a recent report of room-temperature electrical generation using a prototypical spintronic device called the MgO magnetic tunnel junction. This report suggests that, if issues of reproducibility can be overcome, then an already implemented industrial upscaling path could lead to an energy source with an always-on areal power density that is far greater than solar irradiation on Earth. This makes the concept highly disruptive relative to other concepts/initiatives to harvest natural or artificial forms of energy (see below). A timely industrial delivery of this concept could alter our energy-hungry society’s options in the on-going energy transition toward sustainability.

What are magnetic fluctuations?

A ferromagnet is a material in which the magnetic moment of all atoms has aligned along a static direction. This property occurs below the material’s Curie temperature, which can exceed 300˚C for 3d transition metals (Fe, Co, Ni). The best-known ferromagnet is iron.

Ferromagnetism is a collective property: reduce the number of magnetic atoms involved, and a ferromagnetic material can become paramagnetic (PM). In this case, thermal fluctuations cause the on-site magnetic moment to dynamically point along a random direction. Iron nanoclusters can be PM. So can single 3d transition metal atoms within molecules. Alternately, 3d elements like Mn are paramagnetic in thin film form.

Thermal fluctuations may also alter the properties of larger magnetic systems, from nanodots used on hard disk drive platters to skyrmions. From the standpoint of information and communication technologies (ICT), this negatively impacts read/write and retention capabilities of the memory unit.

The proposal here is to harvest the energy involved in these magnetic fluctuations. To do so requires that the magnetic fluctuator be coupled to the device electrodes such that an extremal state of the magnetic fluctuation correspond a preferred direction of charge/spin/heat flow. If the extremal electronic states of the magnetic fluctuator are quantized, then spintronics, which is at its core about favoring the transport of electrons with one spin over the other, can accomplish this preferred current flow. Spintronics implements materials solutions to select an electron spin for transport.

Other energy harvesters compared

It is possible to harvest energy that is either naturally or artificially (i.e. man-made) occurring. Magnetic fluctuations result from the fact that our world bathes in a temperature above absolute zero (T>0 Kelvin). Magnetic fluctuations are therefore occurring naturally. So is solar irradiation from which electricity is generated using the photovoltaic effect in solar cells. Thermal gradients, which occur either naturally (sunshine) or artificially (through an adjacent heat engine), can also be exploited. Harvesting mechanical vibrations, or microwave emissions from GSM and Wi-Fi emitters, are examples of scavenging losses from man-made energy sources, i.e. the harvesting of energy from artificial sources.

The degree to which the energy source is naturally occurring, constraints on its supply (e.g. a solar cell doesn’t operate at night), deployment costs and output power shall determine whether a concept can disrupt the energy storage (thermoelectric, vibrational) and/or energy generation (photovoltaic) markets.

The opposite Table compares the typical power output and constraints of several concepts. Magnetic fluctuations are also listed using the example of paramagnetic fluctuators in a MgO magnetic tunnel junction (MTJ), with a prospective, but not yet achieved, areal power density inferred from published experiments.

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