Swift heavy ion irradiation induced magnetism in magnetically frustrated ${\text{BiMn}}_2{\text{O}}_5$ thin films

The swift heavy ion (SHI) irradiation induces weak ferrimagnetism (FM) in magnetically frustrated polycrystalline ${\text{BiMn}}_2{\text{O}}_5$ thin films. This is manifested from irradiation induced higher energetic configuration that accounts for evolution of the ${\text{Mn}}^{2+}$ state in the ${\text{Mn}}^{3+}/{\text{Mn}}^{4+}$ network. Basically, this is the root of large magnetic moment in the irradiated samples. X-ray diffraction and Raman-scattering data of the samples indicate considerable modifications in the crystal structure after the SHI irradiation. FM in the irradiated samples and magnetically frustrated behavior of the pristine sample is apparent from dc magnetization measurements. Element specific characterizations such as near-edge x-ray absorption fine structure spectroscopy at $\text{O}K$ and $\text{Mn}{L}_{3,2}$ edges along with x-ray magnetic circular dichroism at $\text{Mn}{L}_{3,2}$ edge show the evolution of the ${\text{Mn}}^{2+}$ at disbursement of the ${\text{Mn}}^{4+}$. The microscopic origin behind the induced weak FM is found to be the increased orbital moment in the irradiated thin films.

Figure 1

(Color online) (a) AFM images of pristine as well as irradiated (with fluence values of $5\times {10}^{11}$ and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$) films; (b) Average height distribution obtained from 2D AFM images for pristine and irradiated thin films

Figure 2

(Color online) (a) XRD plots for pristine ${\text{BiMn}}_2{\text{O}}_5/\text{LAO}$ thin film and irradiated with $1\times {10}^{11}$, $5\times {10}^{11}$, and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$ fluence values; reference line 1 and 2 shows the substrate peak and one of the film peak, respectively. (b) Raman spectra for the same samples.

Figure 3

(Color online) Magnetic susceptibility $\left(\chi \right)$ vs $T$ plot measured at 1000 Oe in FC and ZFC cycle for (a) pristine ${\text{BiMn}}_2{\text{O}}_5$ thin film and (b) thin films irradiated with $5\times {10}^{11}$ and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$ fluence values.

Figure 4

(Color online) Magnetization $\left(M\right)$ vs $H$ plot for pristine ${\text{BiMn}}_2{\text{O}}_5$ thin film and thin films irradiated at $5\times {10}^{11}$ and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$ at (a) 300 K and (b) 5 K.

Figure 5

Magnetization $\left(M\right)$ vs $H$ plot for pristine ${\text{BiMn}}_2{\text{O}}_5$ thin film at 5 K, measured after field cooling.

Figure 6

(Color online) Inverse of magnetic susceptibility $\left(1/\chi \right)$ vs $T$ plot for ${\text{BiMn}}_2{\text{O}}_5$ thin films irradiated with $5\times {10}^{11}$ and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$ fluence values.

Figure 7

(Color online) Normalized $\text{Mn}{L}_{3,2}$-edge NEXAFS spectra of pristine ${\text{BiMn}}_2{\text{O}}_5$ thin film and irradiated with $1\times {10}^{11}$, $5\times {10}^{11}$, and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$ fluence values along with the spectra of MnO, ${\text{Mn}}_2{\text{O}}_3$, and ${\text{MnO}}_2$.

Figure 8

(Color online) $\text{Mn}{L}_{3,2}$ edge XMCD spectra at 100 and 300 K for pristine ${\text{BiMn}}_2{\text{O}}_5$ thin film and one irradiated with fluence value of $5\times {10}^{11}\text{ions}/{\text{cm}}^2$.

Figure 9

(Color online) Normalized $\text{O}K$-edge NEXAFS spectra of pristine ${\text{BiMn}}_2{\text{O}}_5$ thin film and irradiated with $1\times {10}^{11}$, $5\times {10}^{11}$, and $1\times {10}^{12}\text{ions}/{\text{cm}}^2$ fluence values at 300 K.