Magnetic particles including ferrimagnetic (FM) and antiferromagnetic (AFM) particles are ubiquitous in the surface of Earth and Mars. The FM particles dominating soil magnetism usually coexist or compete with AFM hematite due to their comparable thermodynamic stability. The uncertain correlation can be modulated by phosphorous (P) absorption during aging of precursor amorphous iron (Fe) oxides. We investigated two Ferralsol sequences around a P mining field with comparable content of hematite but contrasting P/Fe ratio. The FM particles accompanying the formation of hematite are enriched stably at accelerating rates under high P/Fe but at unstably even rates under low P/Fe. The FM particles became less abundant and coarser while the iron oxide crystallinity increased monotonically as P/Fe decreased. We attribute it to more rapid grain growth of FM particles and transformation into hematite without P retarding the crystallization of iron oxides.

Magnetic particles associated with iron (Fe) oxides are widespread on the surface of Earth and Mars and serve as reasonable climatic indicators. Ferrimagnetic maghemite (Mgh) and antiferromagnetic hematite (Hm), which dominate magnetism and redness, often coexist or compete with each other in soils and sediments. The formation efficiency of Mgh relative to Hm could be modulated by geochemical background in addition to climate, especially by phosphate (P), which has a high affinity on the surface of precursor iron oxides in natural systems. We investigated two Ferralsol sequences around a P mining field with comparable climate but contrasting P/Fe ratios. High P/Fe retards iron oxide crystallization as well as grain growth and transformation into Hm, which thereby promotes more effective accumulation of ferrimagnetic Mgh as intermediate products. The ligand-protected effect well interprets asynchronous changes in magnetism and redness in soils and sediments across large spatial and temporal scales.