Study of magnetic and thermal properties of SmCrO₃ polycrystallites

Abstract

In the present work, we have studied the magnetic and thermal properties of sol gel derived samarium chromite (SCO) polycrystallites. The magnetic measurements of SCO polycrystallites show a characteristic antiferromagnetic transition T_N ∼ 190 K and spin reorientation temperature T_SR ∼ 33 K, which is in the region of interest to study a possible magnetocaloric effect (MCE). The isothermal magnetic entropy change (ΔS_M) is estimated by an indirect method from the isothermal magnetization curves measured in this temperature range. The SCO polycrystallites possesses both inverse (positive) and normal (negative) MCE at and above around the spin reorientation transition (T_SR) with −ΔS^max_M values of ∼−24 × 10⁻² & 13 × 10⁻² J kg⁻¹ K⁻¹, respectively. The SCO also shows another normal (negative) MCE peak around its Néel transition (T_N) with −ΔS^max_M ∼ 11 × 10⁻² J kg⁻¹ K⁻¹. The presence of two successive MCE peaks in SCO in the temperature range of 3–50 K, leads to an ∼47 K operating temperature window with one thermodynamic cycle. In addition, the low temperature heat capacity (C_P) measurements of SCO polycrystallites reveal a λ-shaped peak at T_N which is associated with a conventional second-order, paramagnetic to antiferromagnetic (AFM), phase transition. The temperature and magnetic field dependence of the specific heat capacity was studied and analyzed to estimate the adiabatic temperature change (ΔT_ad). In addition the C_P vs. T curve in SCO also shows a weak anomaly around the ∼T_SR along with a Schottky anomaly below 10 K.

---

Introduction

The discovery of the giant magnetocaloric effect (MCE) in Gd₅Si₂Ge₂ reignited the interest in discovering new MCE materials which can work at different temperature ranges, starting from cryogenic temperatures to the vicinity of room temperature (RT) and be used as solid state refrigerants in various applications.¹ Magnetic refrigeration, by eliminating the hazardous gases, appears to be more green, energy efficient and environmentally friendly in comparison with the conventional vapor compression refrigerant technology.² Recent developments in the field of magnetocaloric materials with significant advancement suggest that solid-state refrigeration can become a reality in the near future. However, the challenges associated with understanding and exploring new materials need to be conquered before they can be realised in practical applications.^3,4 The MCE materials show a great potential for investigation of fundamental physical properties besides the technological interest.⁵ In the materials showing the MCE, a temperature change is observed with the change in magnetic field (H) which is usually described as isothermal magnetic entropy change (ΔS_M) or adiabatic temperature change (ΔT_ad).

In an effort towards increasing the ΔS_M, it was realized that the inclusions of superparamagnetic nanoparticles inside the host matrix might enhance the MCE. In the superparamagnetic nanoparticles, it is easy to tune the operating temperature by tuning the blocking transition which is usually determined by the particle size. In addition, large surface area in nanomaterials provide better heat exchange with the surrounding materials. Also, the particle size distribution and interparticle interactions in magnetic nanoparticles lead to the broadening of the entropy change vs. T curve (ΔS_M vs. T) over a wide T-range, thus, enhancing the refrigeration capacity (RC).^6–8

The magnetic materials showing the MCE associated with a first order magnetic transition are quite useful but the issues such as high cost, large thermal hysteresis and, mechanical instability pose challenges. Some of these challenges are overcome by the materials possessing a second order phase transition. An enormous number of materials are reported having large MCE around paramagnetic (PM) to ferromagnetic (FM)/PM to antiferromagnetic (AFM) transition near room temperature and at low temperature.^9–13 Recently, material with AFM–FM transition, spin reorientation transition, ferrimagnetic–FM transition have shown inverse MCE (ΔS_M > 0).^5,14–19

It is well known that MR technology is still in their early development stages, researchers are searching for new materials with excellent MCE properties. In recent years, the rare earth based alloys and oxides are found to be promising candidate for magnetic refrigeration.^20–24 The current adiabatic demagnetization refrigerators (ADR) make use of PM salts which exhibit large MCE below 1 K.^25,26 Hence forth, it is equally important to explore the materials with larger MCE at the cryogenic temperatures. In addition, there is an important class of materials which exhibits normal (ΔS_M < 0) and inverse (ΔS_M > 0) MCE simultaneously. These materials have potential to be employed in magnetic refrigeration technology as both the process i.e. adiabatic magnetization and demagnetization can be employed and hence, improving the refrigeration efficiency to a larger extent. The materials possessing inverse MCE opens up the way for ‘adiabatic magnetization process’ by allowing the sample to cool rather than heat as happens in the conventional materials showing ‘adiabatic demagnetization processes’. Thus, materials with inverse MCE are suggested to be used as heat sinks with the conventional MCE material i.e. ΔS_M < 0, in order to increase the refrigeration efficiency making the device more efficient. Thus, the single-phase materials possessing both normal and inverse MCE are important as these materials rule out the need to make composites. The materials such as Co(FeRu)₂, SmMn₂Ge₂, NaBaMn₂O₆ were reported to show simultaneous normal and inverse MCE enhancing the refrigeration efficiency.^18,27,28 Nevertheless, there exists certain class of material i.e. intermetallics such as Dy₂Cu₂In, Ho₂In which exhibit normal MCE at spin reorientation transition and curie temperature as the temperature change in derivative of magnetization is positive and exchange coupling between sublattices is ferromagnetic giving positive ΔS.^14,29

In past, manganites have been studied for their magnetic properties due to important discoveries such as colossal magnetoresistance etc. In addition, manganites were also explored for MCE related applications as they have an advantage over conventional MCE materials due to high chemical stability, high resistivity, low production cost.^2,30 However, larger heat capacity (C_P) values of manganites such as in case of Ce_0.67Sr_0.33MnO₃ (550 J kg⁻¹ K⁻¹) limits its use.³¹ The large C_P value increases the thermal load therefore, additional energy is required to heat the sample itself, causing a loss of entropy. As C_P is inversely proportional to the ΔT_ad, larger C_P will give smaller ΔT_ad and vice versa.³² Thus, material with smaller C_P value is desirable. Rare earth chromites (RCrO₃, where R: rare earth cations) have attracted much attention recently due to their rich magnetic, ferroelectric properties and possible coupling of both.^33–36 In addition, the unique features, such as negative magnetization (NM), exchange bias (EB) and magnetization switching were observed recently in orthochromites.^34,37–39 Apart from being studied for their multiferroic properties i.e. coexistence of magnetic and electrical property, they were also studied for catalytic properties.^40–42 Recently, RCrO₃ family of compounds have emerged as potential MCE materials as the smaller C_P values (∼95–109 J mol⁻¹ K⁻¹) observed in these materials favor larger ΔT_ad. The ordering of rare earth moments at low temperature makes them advantageous for the MCE refrigeration technology for cryogenic temperature applications.⁴³ Recently, MCE properties of bulk DyCrO₃ were reported by McDannald et al. with a large ΔS_M ∼ 8.1 J kg⁻¹ K⁻¹ at ∼12 K, and relative cooling power (RCP) ∼ 196 J kg⁻¹ at 3 T.¹² Also, giant MCE was observed in single crystal GdCrO₃, with ΔS_M ∼ 31.6 J kg⁻¹ K⁻¹ for a field change of 44 kOe at 3 K.¹¹ It is well known that in rare-earth chromites and manganites, the giant MCE has been observed near the magnetic phase transitions and the MCE can be enhanced by the strong ME coupling.^12,32,44,45 In multiferroic materials, the ME coupling significantly enhances the magnetization, FE polarization, and thus, isothermal entropy change in an FE–FM coupled multiferroic system gets enhanced. The ME coupling introduces additional contribution to ΔT thus, large MCE is observed in a material with strong ME coupling.⁴⁶ The large observed entropy change ∼11.3 J kg⁻¹ K⁻¹ at 4.5 T in DyFe_0.5Cr_0.5O₃ was enhanced by ME coupling due to the magnetic field and temperature induced magnetic transition.¹³

In this work, we have studied the magnetic and thermal property of wet chemically synthesized samarium chromite (SCO) polycrystallites. The previous magnetization studies on SCO polycrystallites, done by us showed the Néel transition (T_N) at ∼190 K and a spontaneous change in magnetic structure at ∼33 K.⁴⁷ The rationale behind choosing the SCO for MCE studies were the magnetic transition such as spin reorientation (SR) and paramagnetic (PM) to antiferromagnetic (AFM) transition temperature which may probably show the coexistence of inverse and normal MCE in a single material. In addition, we have also studied the temperature and field dependent heat capacity studies on SCO polycrystallites and its association with the magnetic anomalies.

Experimental details

Synthesis of SCO polycrystallites

Polycrystalline SmCrO₃ (SCO) polycrystallites were synthesized by a hydrolytic sol–gel method.³⁷ The starting material samarium(III) nitrate hydrate (Sm(NO₃)₃·xH₂O, Aldrich, 99.9% metal basis), chromium nitrate (Cr(NO₃)₃, Thomas Baker, 99.9%) and citric acid were used without any further purification. Stoichiometric amount of Sm(NO₃)₃·xH₂O, Cr(NO₃)₃ and C₆H₈O₇ (molar ratio, 1 : 1) were dissolved in the deionized water and solution was continuously stirred for 3 h to obtain a homogeneous solution. The pH of the solution was raised to ∼9 by adding liquid ammonia drop-wise followed by stirring at room temperature for again 3 h resulting in sol formation due to the formation of metal–citrate complex. The obtained sol was heated at 80 °C and dried gel obtained was calcined at 800 °C and used for further characterization. From our earlier studies, it is found that the X-ray diffraction ruled-out any secondary phase and pattern could be indexed with an orthorhombic perovskite structure according to JCPDS file no. 00-039-0262. The morphological analysis found that the particles are having platelike structure. The detailed results, pertinent to structural and morphological analysis along with magnetic characterization of SCO, have already been published elsewhere.³⁷ We have used the same batch of sample for our MCE and heat capacity studies.

Magnetic measurements

The magnetic measurements of SCO polycrystallites were performed using a Physical Property Measurement System (PPMS) (Quantum Design Inc., San Diego, California equipped with a 9 tesla superconducting magnet). The powder samples were precisely weighed and packed inside a plastic sample-holder which fits into a brass sample holder provided by Quantum Design Inc. with negligible contribution in overall magnetic signal. We collected M–H loops at a rate of 50 Oe s⁻¹ in a field sweep from 0 to 90 kOe at the vibrating frequency of 40 Hz. The M–T was derived from measured M–H curves (1^st quadrant) and was further used to calculate the magnetic entropy change in SCO.

Heat capacity measurements

Thermal relaxation method was used to carry out the heat capacity measurement of SCO and using heat capacity option in PPMS by Quantum Design and change in adiabatic temperature (ΔT_ad) was also determined. For heat capacity measurements, the powder sample was pressed to form a pellet. To ensure a proper thermal contact between the sample and sample platform, and for spanning the temperature from 3–300 K, Apiezon N grease was used. We measured the addenda (only grease) contribution at the zero field so that the heat capacity software can perform an accurate addenda subtraction during sample heat capacity measurements.

Results and discussion

Magnetic study

Arrott plot. To determine the nature of phase transition in SCO, whether, it is a first order or a second order transition, 1^st quadrant isothermal M–H hysteresis measurements are performed to plot H/M vs. M² (Arrott plot) in the region of interest. The material with second order phase transition give curves with positive slope, while, for first order transition, curves with negative slope along with small kinks are observed in the Arrott plot.⁴⁸ Apart from the ordering transition, nature of slope either negative or positive also, depends on the grain size of the sample.^48–50 Competing magnetic interactions in orthochromites is understood to have a contribution from both FM and AFM interactions in magnetic sublattices. The detailed magnetization behavior is already discussed in the case of DCO and similar explanation can be accounted to SCO.^34,37

The Fig. 1 represents the isothermal magnetization hysteresis (M–H) curve (1^st quadrant) measured in various temperature ranges of (a) 3–200 K (ΔT = 2 K), (b) 10–50 K (ΔT = 2 K), and (c) 130–200 K (ΔT = 2 K) with an applied field ramped up to 9 T. The values in parenthesis give temperature step-size. The H/M vs. M² curves (Fig. 2(a)) show change in slope near 20–30 kOe indicating weak FM interaction in SCO. This behavior is similar and consistent with other orthochromites and manganites.^{11,12,44,51–54} The slope of Arrott plot was found to be positive confirming the overall second order phase transition in SCO. The comparison between isotherm curves (inset of Fig. 2(a)) taken at 32 K and 34 K shows a large difference. This is due to the presence of SR transition temperature T_SR at 34 K and usually the magnetic entropy change shows a maximum in the critical region. The Fig. 2(b) and (c) shows the zoom view of Arrott plot at ∼T_N and ∼T_SR, respectively, which is the region of interest for exploring the MCE behavior in SCO.

Fig. 1 (a) The M–H isotherms (1^st quadrant) of SCO polycrystallites measured in temperature ranges of 3–200 K (ΔT = 2 K). The panel (b) 10–50 K (ΔT = 2 K), and (c) 130–200 K (ΔT = 2 K) shows the M–H isotherms with an applied field ramped up to 9 T.

Fig. 2 (a) Arrott plots (H/M vs. M²) of isothermal magnetization. The inset shows the isotherms in a temperature range 30–38 K. (b) The curves show the zoomed view in a temperature range 180–200 K and (c) 32–50 K, respectively.

Magnetocaloric effect. Next, we investigated the MCE behavior in SCO polycrystallites by calculating the entropy change. The MCE is directly proportional to the change in the magnetization as a function of temperature as seen from eqn (1).^1,13,55

It can be inferred from the eqn (1) that larger is a key for larger ΔS_M. The values are extracted from the 1^st quadrant isothermal hysteresis curves and represented in Fig. 3(a) and (b) with a prominent peak at ∼T_SR and ∼T_N which is consistent with the magnetic studies of SCO reported by us earlier.³⁷ After integrating with respect to the field, we obtained ΔS_M values. In Fig. 4(a) and (b) the ΔS_M vs. T curves are plotted in the regions of interest (∼T_SR and ∼T_N). As evident from Fig. 4(a), the ΔS_M is positive at ∼T_SR and becomes negative above and below the T_SR. As expected, the maximum entropy change is seen at 32 K (T_SR). The SCO exhibits positive ΔS_M peak (inverse MCE) around T_SR (32 K) corresponding to the spin reorientation of Sm³⁺ moments with respect to canted Cr³⁺ moments. It was also observed that with increasing magnetic field, ΔS_M peak around T_SR broadens asymmetrically towards the higher temperatures. At 32 K, the −ΔS_M attains a maximum value of −16 × 10⁻² J kg⁻¹ K⁻¹ and −24 × 10⁻² J kg⁻¹ K⁻¹ at 3 T & 5 T applied magnetic fields. In addition, we observe negative peak above and below T_SR covering broad temperature range. However, ΔS_M was found to be negative, at ∼T_N, corresponding to the PM–AFM transition with −ΔS^max_M 11 × 10⁻² J kg⁻¹ K⁻¹ at 5 T as shown in Fig. 4(b).

Fig. 3 Field dependent M–T curves derived from 1^st quadrant isothermal M–H curves shown in temperature ranges (a) 3–50 K and (b) 180–200 K, respectively. The grey shaded portion indicates the spin reorientation transition (∼T_SR) and Néel transition temperature (∼T_N) of SCO.

Fig. 4 The ΔS_M vs. T curves for various magnetic fields for SCO around (a) T_SR and (b) T_N (shown as shaded regions). In the panel (a), the SCO shows successive normal and inverse MCE along with broad range of operating temperature. In the panel (b), the SCO shows a normal MCE around T_N.

Another important parameter, the relative cooling power (RCP) which strongly depends on the ΔS^max_M and full width of half maxima (FWHM) of ΔS_M peak which is given by eqn (2).

RCP = δT_FWMHX|ΔS^max_M| (2)

where, δT_FWMH is full width at half maximum of the peak and |ΔS^max_M| is the maximum entropy change at and above ∼T_SR for 5 T. As shown in Fig. 5(a), the −ΔS^max_M at ∼T_SR (inverse MCE) and above ∼T_SR (normal) was found to be strongly H dependent with ΔS^max_M 24 × 10⁻² & −13 × 10⁻² J kg⁻¹ K⁻¹ at 5 T and increases with increasing H. This interesting MCE behavior in a temperature range 3–50 K, leads to a wide (∼47 K) working temperature range with one thermodynamic cycle (ΔT_cycl = T_hot − T_cold) where, T_hot and T_cold are hot and cold ends of the cycle. The RCP of SCO at and above ∼T_SR was found to be 2.5 and 1.75 J kg⁻¹ at 5 T, respectively as shown in Fig. 5(b).

Fig. 5 (a) The change in the magnetic entropy plotted against the change in field (ΔH) around T_SR for both inverse and normal MCE. (b) The relative cooling power RCP is plotted against the change in field (ΔH) at and above T_SR for SCO.

The Fig. 6(a) and (b) shows the H dependent ΔS_M and RCP plot at ∼T_N, respectively. As seen from figure, −ΔS_M and RCP at ∼T_N was also found to be strongly field dependent with a maximum value 11 × 10⁻² J kg⁻¹ K⁻¹ and 1.18 J kg⁻¹, at 5 T. Although, the ΔS_M and RCP value was found to be less as compared to other chromites such as DyCrO₃ and GdCrO₃, the existence of conventional and IMCE is an added advantage.^11,12

Fig. 6 (a) The change in the magnetic entropy plotted against the change in field (ΔH) at T_N. (b) The relative cooling power RCP is plotted against the change in field (ΔH) at T_N for SCO.

In manganite such as NdBaMn₂O₆, the inverse MCE is related to the PM/FM to AFM transitions.¹⁸ Due to SR transition, compounds such as NdCo₅ and Nd₂Co₇ also show IMCE.^56,57 But, intermetallics such as Dy₂Cu₂In, Ho₂In with SR transition show normal MCE.^14,29 In general, MCE is characterized by the isothermal magnetic entropy change and the adiabatic temperature change upon varying magnetic field. If the temperature derivative of the magnetization is negative, direct MCE is observed, whereas, if it is positive, inverse MCE occurs. Here, the inverse MCE in SCO is expected to occur from the given thermodynamic relation (eqn (1)) in which all thermodynamic quantities are positive (as observed derivative of M versus T in the T_SR region is positive). Unlike other typical materials with SR transition, SCO changes its spin structure at T_SR and the magnetization suddenly drops below T_SR. However, the exchange coupling between Sm³⁺ and Cr³⁺ sublattices is antiferromagnetic, giving IMCE at T_SR. The key characteristic of SCO in the −ΔS_M vs. T curve at ∼T_SR shown in Fig. 4(a) is the successive positive and negative entropy change with increasing temperature, which strongly suggest that both the magnetizing and demagnetizing processes can be employed for cooling, thus increasing the refrigeration efficiency. This feature is due to the fact that spin reorientation transition is often accompanied by inverse MCE.⁹ The successive inverse and normal MCEs in SCO compound could be utilized to stabilize the temperature of a system to ∼35 K due to the change in sign of −ΔS_M around the critical temperature (∼35 K), which most other materials with only normal MCE cannot satisfy.⁵⁸

Then, we explore the universal behavior for the entropy change in SCO with second order phase transition (SOPT) which can be established by scaling the axes appropriately. The universal behavior of SCO polycrystallites was investigated by rescaling the axes for a universal curve, i.e. all ΔS_M curves are normalized with their maximum entropy change (ΔS^max_M), respectively by eqn (3):^59–61

where T_R1 and T_R2 are the reference temperatures where ΔS equals ΔS^max_M/2. The two reference temperatures T_R1 and T_R2, are needed to characterize the entropy change, where T_R1 < T_C and T_R2 > T_C and T_C is the ordering temperature. Here, T_C = ∼T_SR and ∼T_N corresponding to ΔS^max_M. The transformed curves of SCO under various H at ∼T_SR and ∼T_N are plotted in Fig. 7(a) and (b). All the curves collapse into a single curve in temperature regions near to ordering temperature (θ = 0) further validating our treatment of data according to SOPT in SCO. However, as we move away from the ordering temperature where ΔS^max_M is observed, breakdown can be observed in the curve which is acceptable as scaling laws need not hold far away from T ∼ 32 and ∼192 K.

Fig. 7 Normalized entropy change for different applied magnetic fields (1–5 T) for SCO polycrystallites at (a) T_SR and (b) T_N as a function of the rescaled temperatures collapse into a single universal curve.

Heat capacity studies

The zero field temperature dependent of heat capacity for SCO is shown in Fig. 8. The overall shape of C_P–T plot was found to be similar to other chromites such as YbCrO₃, NdCrO₃ etc.^62,63 At high T region, the SCO follows Dulong–Petit law, as C_P approaches to classical value of 3nR (R = molar gas constant, n = 1) per atomic site in formula unit. Fig. 8(a) shows the clear λ shape anomaly at ∼192 K with a weak signature of T_SR at ∼32 K. The C_P of SCO was found to be strongly dependent on temperature and found to be 101.2 J mol⁻¹ K⁻¹ at 300 K which decreases with the temperature and a small hump i.e. Schottky anomaly was observed at ∼4 K. The observed C_P value at 300 K was in good agreement with the reported value of bulk SCO.⁴³ Fig. 8(b) and (c) shows the zoom view of C_P–T at ∼T_N and low temperature (<10 K) clearly indicating the well-defined transition as observed from our previous magnetic studies on SCO.³⁷

Fig. 8 (a) Thermal evolution of heat capacity of SCO polycrystallites at zero field. The zoom view of the thermal anomalies in C_P–T curves observed (b) at T_N and (c) low T (<20 K). The λ shape peak (C_P–T curves) is associated with the second order paramagnetic to antiferromagnetic phase transition.

As total C_P of a system is a combined electronic, lattice and magnetic contribution. The heat capacity of the magnetic material is given by the equation:⁶³

C_P = γT + βT³ + δT^3/2 (4)

where the γT term gives the electronic contribution, βT³ describes the contribution from the lattice and, δT^3/2 gives the spin wave contribution. At low T, as shown in Fig. 9(a), the C_P data is fitted with the above eqn (4) excluding the Schottky anomaly region and good fit was observed. The zero field C_PT^−3/2–T^3/2 plot (Fig. 9(b)) at low T range gives a straight line well in agreement with the experimental data obtained for SCO.

Fig. 9 (a) Experimental C_P data is fitted according to the equation C_P = γT + βT³ + δT^3/2 at low temperature region in zero field condition. (b) The plot of C_PT^−3/2 versus T^3/2 at low temperature regime in zero field gives a straight line showing the presence of magnetic T^3/2 term in heat capacity data. The fitting parameters are mentioned in the plot.

We clearly see a Schottky anomaly in the low temperature regime below 10 K similar to other chromites.^62,63 The observation of a Schottky anomaly indicates that there are small number of discrete energy levels dominating the behavior of a system. When thermal excitation energy is comparable to the energy spacing, the probability of populating the upper level via thermal excitations depends more sensitively on temperature, and thus, we observe a peak in the C_P–T plot, termed as a Schottky anomaly.

Next, we also studied the H dependent C_P–T as shown in Fig. 10. As evident from Fig. 10(a), no significant change in C_P–T with and without applied magnetic field was observed. However, with the increase in applied magnetic field, peak at ∼T_N was suppressed and becomes broader as shown in Fig. 10(b), signifying that the peak is coupled with the magnetic transition. No additional anomaly was observed apart from ∼T_N and ∼T_SR indicating the overall structure of SCO to be AFM. However, below 10 K, we observe Schottky anomaly which was found to be shifted towards higher T with increasing field from 0–3 T (Fig. 10(c)).

Fig. 10 (a) Field dependency of thermal evolution of heat capacity of SCO polycrystallites. (b and c) shows the zoom view of the thermal anomalies at T_N1 and T_N2. For higher applied magnetic field, the peak at T_N1 gets depressed and becomes broader.

It is well known that MCE has a figure of merit which include parameters such as ΔS_M, RCP and ΔT_ad, respectively. The C_P values can also be used to calculate the adiabatic temperature change (T_ad) associated with the magnetic transition in SCO polycrystallites according to the equation given below:

Then, under the assumption that magnetic field dependence of T/C_P(T, H) is much weaker than , which is a quite decent approximation in the transition region, then the adiabatic temperature change can be written as:

The ΔT_ad was calculated using the above equation and was found to be maximum 0.2 K and 0.03 K per 3 T field change at ∼T_SR and ∼T_N, respectively. The T and H dependency of ΔT_ad at ∼T_SR and ∼T_N is shown in Fig. 11(a) and (b).

Fig. 11 The plot of adiabatic temperature change (ΔT_ad) with temperature calculated indirectly from magnetization and heat capacity measurements in a temperature range (a) 3–50 K and (b) 180–200 K for 2 T and 3 T, respectively. The maximum value of ΔT_ad at ∼T_SR and ∼T_N was found to be 0.2 K and 0.03 K/3 T applied field.

Conclusions

We have investigated thermal and magnetic properties of SCO polycrystallites prepared by sol–gel method. We observe successive inverse and normal MCE with −ΔS_M peak at ∼T_SR and ∼T_N are −24 × 10⁻² and 11 × 10⁻² J kg⁻¹ K⁻¹ for a field change of 5 T, respectively. Also, this double peak MCE behavior in SCO in a temperature range 3–50 K, leads to a broader working temperature range (ΔT_cycl ∼ 47 K) with one thermodynamic cycle. The thermal anomaly was found to be consistent with magnetic transition observed in SCO and smaller C_P value at ∼T_SR favor ΔT_ad 0.2 K/3 T field change. The present MCE studies on SCO polycrystallites opens up the way for further exploring other rare earth chromites for possible MCE in addition to multiferroic properties and their attainable cryogenic to room temperature application. This can be achieved by tuning the particle size, chemical substitution etc. in order to shift the transition temperature to room temperature which is subjected to future study. Research is under process in these directions to study the effect of doping on magnetic entropy values and heat capacity behavior across the order–disorder transition.

Acknowledgements

Pankaj Poddar acknowledges support from Young Scientist Award grant from Council for Scientific and Industrial Research (CSIR) in Physical Sciences and a separate grant from Department of Science & Technology (DST), India (DST/INT/ISR/P-8/2011). Preeti Gupta acknowledges the support from the Council of Scientific and Industrial Research (CSIR), India for providing Senior Research Fellowship (SRF).

References

1. K. A. Gschneidner Jr, V. K. Pecharsky and A. O. Tsokol, Rep. Prog. Phys., 2005, 68, 1479–1539.
2. M. H. Phan and S. C. Yu, J. Magn. Magn. Mater., 2007, 308, 325–340.
3. H. Zhang and B.-G. Shen, Chin. Phys. B, 2015, 24, 127504.
4. L. Mañosa, A. Planes and M. Acet, J. Mater. Chem. A, 2013, 1, 4925.
5. P. J. von Ranke, T. S. T. Alvarenga, B. P. Alho, E. P. Nóbrega, P. O. Ribeiro, A. M. G. Carvalho, V. S. R. de Sousa, A. Caldas and N. A. de Oliveira, J. Appl. Phys., 2012, 111, 113916.
6. P. Poddar, J. Gass, D. J. Rebar, S. Srinath, H. Srikanth, S. A. Morrison and E. E. Carpenter, J. Magn. Magn. Mater., 2006, 307, 227–231.
7. S. Srinath, P. Poddar, R. Das, D. Sidhaye, B. L. V. Prasad, J. Gass and H. Srikanth, ChemPhysChem, 2014, 15, 1619–1623.
8. P. Poddar, S. Srinath, J. Gass, B. L. V Prasad and H. Srikanth, J. Phys. Chem. C, 2007, 111, 14060–14066.
9. X. Zhang, B. Zhang, S. Yu, Z. Liu, W. Xu, G. Liu, J. Chen, Z. Cao and G. Wu, Phys. Rev. B: Condens. Matter Mater. Phys., 2007, 76, 2–5.
10. A. Midya, S. N. Das, P. Mandal, S. Pandya and V. Ganesan, Phys. Rev. B: Condens. Matter Mater. Phys., 2011, 84, 235127.
11. L. H. Yin, J. Yang, X. C. Kan, W. H. Song, J. M. Dai and Y. P. Sun, J. Appl. Phys., 2015, 117, 133901.
12. A. McDannald, L. Kuna and M. Jain, J. Appl. Phys., 2013, 114, 113904.
13. L. H. Yin, J. Yang, R. R. Zhang, J. M. Dai, W. H. Song and Y. P. Sun, Appl. Phys. Lett., 2014, 104, 10–15.
14. Q. Zhang, J. H. Cho, B. Li, W. J. Hu and Z. D. Zhang, Appl. Phys. Lett., 2009, 94, 182501.
15. S. Chandra, A. Biswas, S. Datta, B. Ghosh, V. Siruguri, A. K. Raychaudhuri, M. H. Phan and H. Srikanth, J. Phys.: Condens. Matter, 2012, 24, 366004.
16. P. Lemoine, A. Vernière, T. Mazet and B. Malaman, J. Magn. Magn. Mater., 2011, 323, 2690–2695.
17. P. Álvarez-Alonso, P. Gorria, J. A. Blanco, J. Sánchez-Marcos, G. J. Cuello, I. Puente-Orench, J. A. Rodríguez-Velamazán, G. Garbarino, I. de Pedro, J. R. Fernández and J. L. Sánchez Llamazares, Phys. Rev. B: Condens. Matter Mater. Phys., 2012, 86, 184411.
18. Q. Zhang, F. Guillou, A. Wahl, Y. Bŕard and V. Hardy, Appl. Phys. Lett., 2010, 96, 2013–2016.
19. P. Mandal, C. R. Serrao, E. Suard, V. Caignaert, B. Raveau, A. Sundaresan and C. N. R. Rao, J. Solid State Chem., 2013, 197, 408–413.
20. L. Li, M. Kadonaga, D. Huo, Z. Qian, T. Namiki and K. Nishimura, Appl. Phys. Lett., 2012, 101, 122401.
21. L. Li, Y. Yuan, Y. Zhang, T. Namiki, K. Nishimura, R. Pöttgen and S. Zhou, Appl. Phys. Lett., 2015, 107, 132401.
22. L. Li, O. Niehaus, M. Kersting and R. Pöttgen, Appl. Phys. Lett., 2014, 104, 092416.
23. B. Sattibabu, A. K. Bhatnagar, K. Vinod, S. Rayaprol, A. Mani, V. Siruguri and D. Das, RSC Adv., 2016, 6, 48636–48643.
24. Y. Zhang, Y. Yang, X. Xu, L. Hou, Z. Ren, X. Li and G. Wilde, J. Phys. D: Appl. Phys., 2016, 49, 145002.
25. M. Aparnadevi and R. Mahendiran, J. Appl. Phys., 2013, 113, 013911.
26. C. Krishnamoorthi, S. K. Barik, Z. Siu and R. Mahendiran, Solid State Commun., 2010, 150, 1670–1673.
27. M. K. Chattopadhyay, M. A. Manekar and S. B. Roy, J. Phys. D: Appl. Phys., 2006, 39, 1006–1011.
28. Z. Han, H. Wu, D. Wang, Z. Hua, C. Zhang, B. Gu and Y. Du, J. Appl. Phys., 2006, 100, 043908.
29. Y. Zhang, X. Xu, Y. Yang, L. Hou, Z. Ren, X. Li and G. Wilde, J. Alloys Compd., 2016, 667, 130–133.
30. S. Chandra, H. Khurshid, M.-H. Phan and H. Srikanth, Appl. Phys. Lett., 2012, 101, 232405.
31. M. A. Hamad, J. Supercond. Novel Magn., 2013, 26, 2981–2984.
32. M. M. Vopson, J. Phys. D: Appl. Phys., 2013, 46, 345304.
33. A. Jaiswal, R. Das, K. Vivekanand, T. Maity, P. M. Abraham, S. Adyanthaya and P. Poddar, J. Appl. Phys., 2010, 107, 013912.
34. P. Gupta, R. Bhargava, R. Das and P. Poddar, RSC Adv., 2013, 3, 26427.
35. J. R. Sahu, C. R. Serrao, N. Ray, U. V. Waghmare and C. N. R. Rao, J. Mater. Chem., 2007, 17, 42.
36. J. Prado-Gonjal, R. Schmidt, J.-J. Romero, D. Ávila, U. Amador and E. Morán, Inorg. Chem., 2013, 52, 313–320.
37. P. Gupta, R. Bhargava and P. Poddar, J. Phys. D: Appl. Phys., 2015, 48, 025004.
38. P. K. Manna and S. M. Yusuf, Phys. Rep., 2014, 535, 61–99.
39. A. Kumar and S. M. Yusuf, Phys. Rep., 2015, 556, 1–34.
40. K. Sardar, M. R. Lees, R. J. Kashtiban, J. Sloan and R. I. Walton, Chem. Mater., 2011, 23, 48–56.
41. V. Srinu Bhadram, B. Rajeswaran, A. Sundaresan and C. Narayana, Europhys. Lett., 2013, 101, 17008.
42. P. Gupta and P. Poddar, RSC Adv., 2015, 5, 10094–10101.
43. H. Satoh, S. Koseki, M. Takagi, W. Yang Chung and N. Kamegashira, J. Alloys Compd., 1997, 259, 176–182.
44. A. Midya, S. N. Das, P. Mandal, S. Pandya and V. Ganesan, Phys. Rev. B: Condens. Matter Mater. Phys., 2011, 84, 1–10.
45. M. Shao, S. Cao, S. Yuan, J. Shang, B. Kang, B. Lu and J. Zhang, Appl. Phys. Lett., 2012, 100, 222404.
46. M. M. Vopson, Solid State Commun., 2012, 152, 2067–2070.
47. G. Gorodetsky, R. M. Hornreich, S. Shaft, B. Sharon, A. Shaulov and B. M. Wanklyn, Phys. Rev. B: Solid State, 1977, 16, 515–521.
48. A. Arrott, Phys. Rev., 1957, 108, 1394–1396.
49. A. K. Pramanik and A. Banerjee, Phys. Rev. B: Condens. Matter Mater. Phys., 2010, 82, 1–9.
50. A. Arrott and J. E. Noakes, Phys. Rev. Lett., 1967, 19, 786–789.
51. L. H. Yin, J. Yang, R. R. Zhang, J. M. Dai, W. H. Song and Y. P. Sun, Appl. Phys. Lett., 2014, 104, 032904.
52. B. Tiwari, M. K. Surendra and M. S. Ramachandra Rao, J. Phys.: Condens. Matter, 2013, 25, 216004.
53. M.-H. Phan and S.-C. Yu, J. Magn. Magn. Mater., 2007, 308, 325–340.
54. N. Pavan Kumar and P. Venugopal Reddy, Mater. Lett., 2014, 132, 82–85.
55. M. Shao, S. Cao, S. Yuan, J. Shang, B. Kang, B. Lu and J. Zhang, Appl. Phys. Lett., 2012, 100, 222404.
56. S. A. Nikitin, K. P. Skokov, Y. S. Koshkid'Ko, Y. G. Pastushenkov and T. I. Ivanova, Phys. Rev. Lett., 2010, 105, 1–4.
57. M. Ilyn, M. I. Bartashevich, a. V. Andreev, E. a. Tereshina, V. Zhukova, A. Zhukov and J. Gonzalez, J. Appl. Phys., 2011, 109, 083932.
58. H. Zhang, Y. J. Sun, L. H. Yang, E. Niu, H. S. Wang, F. X. Hu, J. R. Sun and B. G. Shen, J. Appl. Phys., 2014, 115, 063901.
59. C. M. Bonilla, J. Herrero-Albillos, F. Bartolomé, L. M. García, M. Parra-Borderías and V. Franco, Phys. Rev. B: Condens. Matter Mater. Phys., 2010, 81, 224424.
60. Q. Y. Dong, H. W. Zhang, J. R. Sun, B. G. Shen and V. Franco, J. Appl. Phys., 2008, 103, 101–104.
61. V. Franco, J. S. Blázquez, B. Ingale and A. Conde, Annu. Rev. Mater. Res., 2012, 42, 305–342.
62. Y. Su, J. Zhang, Z. Feng, L. Li, B. Li, Y. Zhou, Z. Chen and S. Cao, J. Appl. Phys., 2010, 108, 013905.
63. Y. Du, Z. X. Cheng, X.-L. Wang and S. X. Dou, J. Appl. Phys., 2010, 108, 093914.

---