Magnetism has captivated humanity for thousands of years, leading to the development of numerous technological applications. From compasses to electric motors and generators, ferromagnetism has been the driving force behind these devices. However, as fundamental research delves deeper into magnetism, there is a growing interest in exploring other forms of this phenomenon. These alternative forms of magnetism have the potential to revolutionize secure data storage and serve as platforms for quantum computers. Unfortunately, discovering and fully controlling novel types of magnetism is an incredibly complex undertaking, as acknowledged by Andrej Pustogow, the leader of an international research team based at TU Wien.
To understand the groundbreaking research led by Pustogow and his team, it is crucial to grasp the concept of spins. Spins can be visualized as tiny compass needles that align themselves in response to an external magnetic field and generate their own magnetic field. In ferromagnetism, which underlies permanent magnets, all electron spins align parallel to one another. However, in certain crystal lattice arrangements, such as ordinary square or checkerboard-type lattices, an anti-parallel alignment of spins is possible. These arrangements consist of neighboring spins pointing alternately in opposite directions. The complexity arises when dealing with triangular lattices or lattices with triangular structures, like the intricate kagome lattice. In these scenarios, a completely antiparallel arrangement is not feasible. Instead, if two corners of a triangle possess opposite spin directions, the remaining side must match one of the two directions. Both spin up and spin down options are equally valid. This intriguing characteristic is known as “geometrical frustration” and is prevalent in crystal structures with electron spins organized in triangular, kagome, or honeycomb lattices. Consequently, randomly arranged spin pairs form, leaving some spins unpaired. These unpaired magnetic moments can potentially be harnessed for data storage or computational operations in quantum computers when manipulated with external magnetic fields.
While the concept of geometrical frustration and its implications hold tremendous promise, achieving precise control over magnetic properties in real materials remains a significant challenge. In order to fully exploit the potential of magnetic fields for data storage and quantum computing, scientists must accurately control the symmetry of the crystal lattice and, consequently, the magnetic properties. Although it is possible to manufacture materials with strong geometrical frustration, seamlessly transitioning from weak to strong frustration and vice versa within a single crystal has remained elusive. This is where Pustogow’s research breaks new ground.
Pustogow and his team sought to change the magnetism in a material “by pushing a button,” and they achieved this by subjecting the crystal to pressure. By applying uniaxial stress and deforming the crystal lattice from its original kagome structure, the researchers were able to alter the magnetic interactions between electrons. The application of mechanical pressure effectively coerced the system into a preferred magnetic direction, reducing the level of frustration. This reduction in frustration can be likened to real-life situations where stress diminishes because it imposes a decision on individuals, relieving them of the burden of making the choice themselves.
The implications of the research are significant. The team succeeded in raising the temperature of the magnetic phase transition by over 10%. While this may seem inconsequential at first glance, one should consider the consequences of increasing the freezing point of water by 10%. Imagine water freezing at 27°C instead of 0°C – the world as we know it would be drastically altered. This achievement demonstrates the potential of actively controlling geometrical frustration through mechanical stress, opening the door to unprecedented manipulations of material properties.
A Glimpse into the Future
Having reduced geometrical frustration in their experiments, Pustogow and his colleagues now aim to reverse the process and increase frustration to the point where antiferromagnetism is completely eliminated. This endeavor could pave the way for the realization of a quantum spin liquid, a highly sought-after state of matter with extraordinary properties. By utilizing uniaxial mechanical stress to fine-tune the level of frustration within the crystal lattice, researchers could achieve remarkable control over material properties. The ability to toggle magnetism “by pushing a button” represents a remarkable stride towards harnessing the full potential of magnetism for technological advancement.
Through their pioneering research, Andrej Pustogow and his team at TU Wien have provided valuable insights and breakthroughs in the world of magnetism. By continuously changing the magnetic interactions in a crystal through the application of pressure, they have demonstrated the ability to control magnetism “by pushing a button.” This capability opens up new avenues for exploring novel forms of magnetism and materials with practical applications in secure data storage and quantum computing. With further advancements on the horizon, the future of magnetism indeed holds exciting possibilities.
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