Reactivity of magnetized materials
Magnetization as a process condition (during synthesis procedure) can affect the crystal structure and nanoparticle size and morphology which in turn can affect accessibility of reactive sites. See the following papers:

Hu, Dawei, Yanmin Wang, and Qi Song. "Weakly magnetic field-assisted synthesis of magnetite nano-particles in oxidative co-precipitation." Particuology 7.5 (2009): 363-367.

Xiao, W., et al. "Magnetic-field-assisted synthesis of magnetite nanoparticles via thermal decomposition and their hyperthermia properties." CrystEngComm 17.19 (2015): 3652-3658.

Li, Yang, et al. "Fe 3 O 4@ PSC nanoparticle clusters with enhanced magnetic properties prepared by alternating-current magnetic field assisted co-precipitation." Colloids and Surfaces A: Physicochemical and Engineering Aspects 520 (2017): 348-354.