*A*-site disorder driven sharp field-induced transition and collapse of charge ordering in Sm

_{1/2}Ca

_{1/2-x }Sr

_{ x }MnO

_{3}

^{1}, A. Karmakar

^{1}, S. Majumdar

^{1}, S. Giri

^{1,a)}, S. Das

^{2}and V. S. Amaral

^{2}

### Abstract

Our study on (*x* = 0, 1/6, 1/3, and 1/2) system shows an unusual consequence in magnetic field-induced transition to ferromagnetic metallic state and collapse of charge ordering in the intermediate compositions. Interestingly, the transition is sharp or step-like at low temperature that is observed at much lower field (75 kOe) for intermediate compositions than the end compositions (not visible up to 100 kOe). The atomic-scale local inhomogeneity/distortion arising from ionic mismatch due to doping is supposed to be critical behind this field-induced transition. The charge ordering temperature observed from magnetization and magnetoresistance studies decreases with increasing *x* which is consistent with the results for (*R* = La − Sm, *A* = Ca, Sr) family.

S.G. wishes to thank CSIR, India (Project No. 03(1167)/10/EMR-II) for the financial support and Unit of Nanoscience of IACS funded by DST, India for providing MPMS facility. S.S. also wishes to thank CSIR, India for the JRF. S.D acknowledges Foundation of Science and Technology (FCT) of Portugal for the postdoctoral grant.

I. INTRODUCTION

II. EXPERIMENT

III. RESULTS AND DISCUSSIONS

A. Structural properties

B. Magnetic properties

C. Electrical transport properties

IV. SUMMARY AND CONCLUSIONS

### Key Topics

- Atomic force microscopy
- 6.0
- Magnetoresistance
- 6.0
- Curie point
- 5.0
- Magnetic fields
- 5.0
- Doping
- 4.0

## Figures

X-ray diffraction patterns of (black symbols) at *x* = 0 (a), 1/6 (b), 1/3 (c), and 1/2 (d) at 300 K with the fit from Rietveld refinement (red curve). Blue plot is the residual. Green bars show the peak positions.

X-ray diffraction patterns of (black symbols) at *x* = 0 (a), 1/6 (b), 1/3 (c), and 1/2 (d) at 300 K with the fit from Rietveld refinement (red curve). Blue plot is the residual. Green bars show the peak positions.

Plot of with along with the reported results.^{29} Data representing open circles are obtained from the current investigation.

Plot of with along with the reported results.^{29} Data representing open circles are obtained from the current investigation.

Temperature variations of ZFC-FC magnetization measured at 100 Oe for *x* = 0 (a), 1/6 (b), 1/3 (c), and 1/2 (d) in are plotted in semi-log scale. Solid and open symbols represent the ZFC and FC data, respectively. Signature of is indicated by the arrows.

Temperature variations of ZFC-FC magnetization measured at 100 Oe for *x* = 0 (a), 1/6 (b), 1/3 (c), and 1/2 (d) in are plotted in semi-log scale. Solid and open symbols represent the ZFC and FC data, respectively. Signature of is indicated by the arrows.

Temperature variation of at *f* = 3, 11, and 112 Hz for *x* = 1/3. Upper and lower insets show the enlarged low-temperature and high-temperature peaks, respectively, at different *f*.

Temperature variation of at *f* = 3, 11, and 112 Hz for *x* = 1/3. Upper and lower insets show the enlarged low-temperature and high-temperature peaks, respectively, at different *f*.

Variations of (unfilled symbols) with obtained from the results of the end members in (Ca,Sr) (triangles),^{10,11} (Ca,Sr) (squares),^{12–14,37} and (Ca,Sr) (diamonds).^{15–18} The data obtained from the current investigation are given by the filled symbols.

Variations of (unfilled symbols) with obtained from the results of the end members in (Ca,Sr) (triangles),^{10,11} (Ca,Sr) (squares),^{12–14,37} and (Ca,Sr) (diamonds).^{15–18} The data obtained from the current investigation are given by the filled symbols.

Magnetization curves at 45 K for *x* = 1/6, 1/3, and 1/2 measured at a field sweep rate, 2 kOe/min (a) and at 4 K for *x* = 0, 1/6, 1/3, and 1/2 measured at a field sweep rate, 5 kOe/min (b) of .

Magnetization curves at 45 K for *x* = 1/6, 1/3, and 1/2 measured at a field sweep rate, 2 kOe/min (a) and at 4 K for *x* = 0, 1/6, 1/3, and 1/2 measured at a field sweep rate, 5 kOe/min (b) of .

The *H–T* phase diagram of at *x* = 1/6 and 1/3. The values of critical field () during increasing (solid) and decreasing (open) field cycles taken from the measurements at sweep rate of 2 kOe/min. Squares and triangles represent the data for *x* = 1/3 and 1/6, respectively.

The *H–T* phase diagram of at *x* = 1/6 and 1/3. The values of critical field () during increasing (solid) and decreasing (open) field cycles taken from the measurements at sweep rate of 2 kOe/min. Squares and triangles represent the data for *x* = 1/3 and 1/6, respectively.

Temperature variation of resistivity in zero-field at different *x* in .

Temperature variation of resistivity in zero-field at different *x* in .

MR-*H* curves at 40 K measured in sweep mode at a rate of 5 kOe/min at 40 K (a) and 50 K (b) for *x* = 1/6 and 1/3, respectively.

MR-*H* curves at 40 K measured in sweep mode at a rate of 5 kOe/min at 40 K (a) and 50 K (b) for *x* = 1/6 and 1/3, respectively.

MR-*H* curves at 5 K measured in sweep mode at a rate of 5 kOe/min at *x* = 1/6 (a) and 1/3 (b) for .

MR-*H* curves at 5 K measured in sweep mode at a rate of 5 kOe/min at *x* = 1/6 (a) and 1/3 (b) for .

## Tables

Crystallographic parameters with *Pnma* space group and orthorhombic structure obtained from the Rietveld refinement of x-ray diffraction patterns of at 300 K. The atomic positions of Mn are at (0, 0, 0.5), Sm/Ca/Sr at (X, 0.25, Z), and O1 and O2 at (X, 0.25, Z) and (X, Y, Z), respectively.

Crystallographic parameters with *Pnma* space group and orthorhombic structure obtained from the Rietveld refinement of x-ray diffraction patterns of at 300 K. The atomic positions of Mn are at (0, 0, 0.5), Sm/Ca/Sr at (X, 0.25, Z), and O1 and O2 at (X, 0.25, Z) and (X, Y, Z), respectively.

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