A research team led by Prof. SHENG Zhigao from the Hefei Institutes of Physical Science, Chinese Academy of Sciences, in collaboration with Prof. NIE Yuefeng' s team at Nanjing University, has found that releasing strain can speed up ultrafast demagnetization in freestanding SrRuO3 membranes, while a tiny gap between the membrane and its substrate can slow down magnetization recovery.
The experiments were conducted at the Steady High Magnetic Field Facility using superconducting magnet SM1.
The findings were published in Small.
SrRuO3 is an important material for oxide spintronics, but its magnetic response can be affected by both strain from the substrate and heat transfer across the interface. Freestanding membranes, which are released from the substrate, allow researchers to examine these effects separately.
In this study, the team fabricated SrRuO3 films about 20 nanometers thick in both freestanding and substrate-supported forms. They then used time-resolved magneto-optical Kerr effect (TR-MOKE) spectroscopy to compare how the films responded to laser excitation.
The two types of films showed different magnetic responses. The freestanding membranes lost their magnetization in a single step within about 1 picosecond, while the substrate-supported films showed a two-step process.
Analysis using a microscopic three-temperature model showed that releasing the strain reduces the magnetic moment of SrRuO3. This allows the freestanding membranes to demagnetize about twice as fast as the substrate-supported films.
However, faster demagnetization did not mean faster recovery. The researchers found that a nanometer-scale gap between the freestanding membrane and its substrate hinders heat transfer. Heat therefore remains in the membrane longer, slowing the recovery of its magnetization.
The findings show that strain and heat transfer at the interface affect ultrafast magnetization in different ways, according to the team.
Ultrafast magnetization dynamics and interfacial schematics of freestanding and epitaxial SrRuO3 films. (Image by LU Qinwen)
