The crystal of perovskite iridate SrIrO₃ resembles a row of soldiers, where each iridium carries a magnetic moment. When some of the iridium 'soldiers' are replaced by tin, which has no magnetic moment, the row thins out. Using resonant inelastic X-ray scattering, a method where an X-ray photon transfers part of its energy to excite magnetic oscillations, scientists tracked how these oscillations change as dilution goes from 0 to 20 percent.
It turned out that the energy of magnetic oscillations smoothly decreases as the tin fraction increases. This is like a tuning fork sounding quieter when dipped into a viscous liquid: the magnetic bonds between iridium atoms weaken, and the oscillations damp out. From the data, they extracted effective exchange interactions — a measure of the magnetic coupling strength between neighboring atoms. Their evolution follows a simple scaling law: the coupling strength is proportional to the fraction of remaining magnetic ions raised to the power of about 1.5.
This result is important not only for understanding this specific material. It shows that in SrIrO₃, electrons interact strongly with each other, and their charge dynamics are tightly intertwined with spin dynamics. When we alter the magnetic subsystem, the electronic conductivity responds. Such intertwining is key to creating materials with tunable magnetic and electronic properties, for example, for spintronics, where information is carried not by charge but by the electron's spin.
Replacing just 3% of iridium atoms with tin already noticeably reduces the energy of magnetic oscillations — by about 10%.