Magnetism dynamics driven by phase separation in Pr-doped manganite thin films: A ferromagnetic resonance study

We performed ferromagnetic resonance measurements of a ${\left({\mathrm{La}}_{1-x}{\mathrm{Pr}}_x\right)}_{1-y}{\mathrm{Ca}}_y\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ with $x=0.52\pm 0.05, y=0.23\pm 0.04$, and $\delta =0.14\pm 0.10$ thin single crystalline film which, in combination with micromagnetic simulations, reveal three temperature regions consistent with (i) a ferromagnetic-paramagnetic transition in which ferromagnetic domains nucleate and grow, (ii) followed by a filamentary fluidlike percolation of magnetic domains exhibiting dynamic processes and finally, iii) the existence of a blocking temperature below which the magnetism is a metastable glassy-like state with strong decoherence of the uniform resonance mode. Our results suggest a strain-liquid to strain-glass spin order transition in which the magnetism and fluidlike dynamics of the separated phases freeze at low temperatures. We show the magnetism dynamics depend strongly on the phase-separated state and morphology of the magnetic domains suggesting a route to control of phase separation and realization of spintronic and magnonic devices.

Figure 1

(a) Density plot of the FMR signal as a function of temperature for cooling. In the temperature regions A, B, C, and D qualitatively different behavior is observed. Square symbols correspond to fitted resonant field at selected temperatures. The various resonance fields are obtained from the fitted FMR signals (Fig. 2). The inset shows the orientation of the LPCMO thin film and NGO substrate, as well as the orientation of the dc magnetic field ($H_{\mathrm{dc}}$) and microwave field ($H_{\mathrm{ac}}$) in the FMR experiment. (b), (c), (d), and (e) show FMR curves for specific temperatures in regions A, B, C, and D, respectively. The EPR and FMR signals in (b) are denoted with diamond and square symbols, respectively. The circle symbol indicates an unexpected FMR signal. (f) Resistance as a function of temperature for cooling.

Figure 2

(a) Resonant field, (c) linewidth, and (e) intensity data fitted from the FMR density plot of the Fig. 1. Respective highlighted narrow temperature regions are shown in detail in (b), (d), and (f). Both modes in such region are denoted as M1 and M2.

Figure 3

(a) Experimental FMR signal in the paramagnetic region A. Symbol diamond indicates the typical EPR signal. Circle and square symbols indicate weak FMR signals. (b) Calculated FMR signal (denoted by $H_{\mathrm{R}}$) in region B, where the size of ferromagnetic regions increases while cooling and decreases while warming. (c) FMR simulation in region C for cooling, assuming the percolation of ferromagnetic regions (the upper figure shows the simulated system). (d) FMR simulation in region C for warming (the lower figure shows the simulated system). (e) FMR simulation for a system where ferromagnetic regions percolate. The FMR signal becomes weaker (like in the experimental region D) with increasing Gilbert damping.

Figure 4

(a) Experimental FMR signal between 77 and 71 K (region C) for cooling. (b) FMR simulation for the modeled four systems of (c).