^{1}and R. Mahendiran

^{1,a)}

### Abstract

We report electrical resistivity, magnetic, and magnetocaloric properties in Sm_{0.7−x}La_{x}Sr_{0.3}MnO_{3} series for x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, and 0.7. All the compounds show second order paramagnetic to ferromagnetic (FM) transition at *T* = *T _{c} _{,} * which is tunable anywhere between 83 K and 373 K with a proper choice of the doping level (x). The insulating ferromagnet x = 0 transforms to a ferromagnetic metal below

*T*for x = 0.1, and the insulator-metal transition temperature shifts up with increasing x. The magnetization (

_{c}*M*) exhibits an interesting behavior as a function of temperature and doping level. The field-cooled

*M*(

*T*) of all but x = 0.7 compounds show a cusp at a temperature

*T**much below

*T*. While the

_{c}*T*increases monotonically with increasing x,

_{c}*T** increases gradually, attains a maximum value (

*T** = 137 K) for x = 0.6 and decreases rapidly thereafter. It is suggested that the decrease of

*M*(

*T*) below

*T** is due to ferrimagnetic interaction between Sm(4f) and Mn(3d) sublattices that promotes spin-reorientation transition of the Mn-sublattice. The observed anomalous feature in

*M*(

*T*) does not have impact on the dc resistivity. Magnetic entropy change (Δ

*S*) was estimated from magnetization isotherms. The sign of Δ

_{m}*S*is found to change from negative above

_{m}*T** to positive below

*T** indicating the coexistence of normal and inverse magnetocaloric effects. Δ

*S*is nearly composition independent (−Δ

_{m}*S*= 1.2 ± 0.2 J/Kg K for μ

_{m}_{0}Δ

*H*= 1 Tesla) and refrigeration capacity lies between 40 and 50 J/kg K for 0.1 ≤ x ≤ 0.6. We show scaling of magnetic entropy change under different magnetic fields and analysis of critical exponents associated with the phase transition in x = 0.6 compound. The tunability of Curie temperature with nearly constant Δ

*S*value along with high refrigeration capacity makes this series of compounds interesting for magnetic refrigeration over a wide temperature range.

_{m}R.M. acknowledges the National Research Foundation, Singapore (Grant no. NRF-CRP-G-2007-12) for supporting this work.

I. INTRODUCTION

II. EXPERIMENTAL DETAILS

III. RESULTS AND DISCUSSION

A. Structure

B. Resistivity

C. Magnetization

D. Magnetocaloric effect

E. Critical behavior near the phase transition

IV. DISCUSSION

V. CONCLUSION

### Key Topics

- Curie point
- 22.0
- Ferromagnetism
- 20.0
- Ferromagnetic materials
- 17.0
- Entropy
- 16.0
- Electrical resistivity
- 15.0

##### F25B

##### F25B21/00

##### H01F1/00

##### H01F13/00

## Figures

X-ray diffraction pattern of Sm_{0.7−x}La_{x}Sr_{0.3}MnO_{3} (x = 0–0.7) compounds.

X-ray diffraction pattern of Sm_{0.7−x}La_{x}Sr_{0.3}MnO_{3} (x = 0–0.7) compounds.

Phase diagram for Sm_{0.7−x}La_{x}Sr_{0.3}MnO_{3} (x = 0–0.7) as a function of tolerance factor *t* and composition x*. T _{c} * and

*T*correspond to ferromagnetic Curie temperature of the Mn-sublattice and occurrence of a cusp in the field-cooled magnetization measured at μ

^{*}_{0}

*H*= 1 kOe, respectively.

Phase diagram for Sm_{0.7−x}La_{x}Sr_{0.3}MnO_{3} (x = 0–0.7) as a function of tolerance factor *t* and composition x*. T _{c} * and

*T*correspond to ferromagnetic Curie temperature of the Mn-sublattice and occurrence of a cusp in the field-cooled magnetization measured at μ

^{*}_{0}

*H*= 1 kOe, respectively.

(a) Temperature dependence of the resistivity *ρ(T)* of x = 0–0.6 in zero magnetic field. The inset shows the activation energy for polaron hopping with varying x. (b) ln(ρ/T) versus 1/T plots with linear fit at high temperatures for x = 0 and 0.1.

(a) Temperature dependence of the resistivity *ρ(T)* of x = 0–0.6 in zero magnetic field. The inset shows the activation energy for polaron hopping with varying x. (b) ln(ρ/T) versus 1/T plots with linear fit at high temperatures for x = 0 and 0.1.

(a) Field-cooled magnetization *M*(*T*) for x = 0–0.7 under *H* = 1 kOe. (b) *M*(*H*) at 10 K for x = 0, 0.1, 0.4, and 0.6. The inset (i) shows dependence of magnetization value at 5 T at 10 K on composition. The inset (ii) shows *T _{c} * and

*T*as a function of composition x.

^{*}(a) Field-cooled magnetization *M*(*T*) for x = 0–0.7 under *H* = 1 kOe. (b) *M*(*H*) at 10 K for x = 0, 0.1, 0.4, and 0.6. The inset (i) shows dependence of magnetization value at 5 T at 10 K on composition. The inset (ii) shows *T _{c} * and

*T*as a function of composition x.

^{*} *M*(*H*) plots at selected temperatures for x = (a) 0, (b) 0.1, (c) 0.5, and (d) 0.6 compounds.

*M*(*H*) plots at selected temperatures for x = (a) 0, (b) 0.1, (c) 0.5, and (d) 0.6 compounds.

Temperature dependence of the magnetic entropy (Δ*S _{m} *) obtained from

*M*(

*H*) data at μ

_{0}Δ

*H*= (a) 1 T and (b) 5 T for x = 0 to 0.7. Inset shows the variation of maximum magnetic entropy with magnetic field for all compositions.

Temperature dependence of the magnetic entropy (Δ*S _{m} *) obtained from

*M*(

*H*) data at μ

_{0}Δ

*H*= (a) 1 T and (b) 5 T for x = 0 to 0.7. Inset shows the variation of maximum magnetic entropy with magnetic field for all compositions.

Values of (a) Δ*S _{m} * at

*T*and (b) refrigerant capacity (RC) for μ

_{c}_{0}Δ

*H*= 1, 2, and 5 T and (c)

*T*as a function of composition x. (d) Normalized Δ

_{c}*S*versus

_{m}*T*/

*T*for different x.

_{c}Values of (a) Δ*S _{m} * at

*T*and (b) refrigerant capacity (RC) for μ

_{c}_{0}Δ

*H*= 1, 2, and 5 T and (c)

*T*as a function of composition x. (d) Normalized Δ

_{c}*S*versus

_{m}*T*/

*T*for different x.

_{c}Arrott plots (μ_{0} *H*/*M* vs. *M* ^{2}) of isothermal magnetization. Inset shows isothermal (−Δ*S* _{m}) vs *M* ^{2} curve of Sm_{0.1}La_{0.6}Sr_{0.3}MnO_{3}.

Arrott plots (μ_{0} *H*/*M* vs. *M* ^{2}) of isothermal magnetization. Inset shows isothermal (−Δ*S* _{m}) vs *M* ^{2} curve of Sm_{0.1}La_{0.6}Sr_{0.3}MnO_{3}.

(a) Spontaneous magnetization and inverse initial susceptibility deduced by extrapolating Arrott plot (μ_{0} *H*/*M* vs. *M* ^{2}) to μ_{0} *H* = 0 and *M* ^{2} = 0, respectively. Solid lines are best fits to the equations *M* _{s}(*T*) = *M* _{0}| *ε* |^{β} and χ_{0} ^{−1} (*T*) = (*h _{0} */

*M*)

_{0}*ε*. (b) Spontaneous magnetization of Sm

^{γ}_{0.1}La

_{0.6}Sr

_{0.3}MnO

_{3}estimated from (−Δ

*S*

_{m}) vs

*M*

^{2}curve and Arrott plots.

(a) Spontaneous magnetization and inverse initial susceptibility deduced by extrapolating Arrott plot (μ_{0} *H*/*M* vs. *M* ^{2}) to μ_{0} *H* = 0 and *M* ^{2} = 0, respectively. Solid lines are best fits to the equations *M* _{s}(*T*) = *M* _{0}| *ε* |^{β} and χ_{0} ^{−1} (*T*) = (*h _{0} */

*M*)

_{0}*ε*. (b) Spontaneous magnetization of Sm

^{γ}_{0.1}La

_{0.6}Sr

_{0.3}MnO

_{3}estimated from (−Δ

*S*

_{m}) vs

*M*

^{2}curve and Arrott plots.

Normalised Δ*S _{m} * versus normalized temperature

*θ*for different applied magnetic fields for Sm

_{0.1}La

_{0.6}Sr

_{0.3}MnO

_{3.}

Normalised Δ*S _{m} * versus normalized temperature

*θ*for different applied magnetic fields for Sm

_{0.1}La

_{0.6}Sr

_{0.3}MnO

_{3.}

## Tables

Structural parameters calculated from X-ray diffraction data. BL is the average Mn-O bond length.

Structural parameters calculated from X-ray diffraction data. BL is the average Mn-O bond length.

Ferromagnetic Curie temperature (*T _{C} *), activation energy (E

_{ρ}), maximum entropy change (Δ

*S*), and refrigerant capacity (

_{m}*RC*) for different compositions.

Ferromagnetic Curie temperature (*T _{C} *), activation energy (E

_{ρ}), maximum entropy change (Δ

*S*), and refrigerant capacity (

_{m}*RC*) for different compositions.

Magnetocaloric parameters at the Curie temperature *T _{C} * for different manganites.

Magnetocaloric parameters at the Curie temperature *T _{C} * for different manganites.

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