Effects of sweep rates of external magnetic fields on the labyrinthine instabilities of miscible magnetic fluids

►Interfacial instability of miscible magnetic fluids in a Hele-Shaw cell is investigated. ►Effects of magnitudes and sweep rates of the external magnetic field are studied experimentally. ►External uniform magnetic fields induce labyrinthine fingering instability and secondary waves. ►A Peclet number including diffusion and sweep rate effects is found to correlate experimental data. ►Initial growth rate of interfacial length is linearly proportional to Pe at onset of instability.