Speaker
Description
Doping of transition metal oxides provides a controlled route for tuning the charge, spin, and lattice degrees of freedom, thereby enabling the tailoring of magnetic and electronic functionalities of the material. However, local probe studies of powder samples remain challenging due to strong electron correlation effects and charge/spin dynamics, obscuring the fine spectroscopic properties. Weakly doped high-pressure-grown CaFe$_3$O$_5$ was shown to segregate into two distinct electronic phases with different antiferromagnetic orderings. At the same time, the samples exhibit weak ferromagnetism, likely arising from canting of spin chains, and the relationship between ferromagnetism and phase segregation remains an open question.
For the study of Mn-doped CaFe$_3$O$_5$, we employ quantum magnetometry based on nitrogen-vacancy (NV) centres in nanodiamonds, impressed into the doped CaFe$_3$O$_5$ powder pellet to probe both static and dynamic magnetic fields across the weak ferromagnetic transition. The optically detected magnetic resonance (ODMR) spectra of the NV ensemble show additional broadening and splitting below the critical transition temperature T$_c$ = 290 K. At the same time, the spin-lattice relaxation increases drastically at T$_c$, a signature of enhanced magnetic fluctuations.
Microscopic modelling of ODMR spectra reveals signatures of a weakly ferromagnetic phase coexisting with an antiferromagnetic phase. By relating the magnetic spectra with electronic phase fractions determined from neutron scattering, we find the majority phase to be a likely candidate for spin canting, resulting in weak ferromagnetism. The presented study demonstrates the viability of using nanodiamonds as a low-cost platform for magnetic measurements in solid-state systems.