Effect of hydrostatic pressure on the magnetic, exchange bias and magnetocaloric properties of Ni45.5Co2Mn37.5Sn15

Accepted Manuscript Effect of hydrostatic pressure on the magnetic, exchange bias and magnetocaloric properties of Ni45.5Co2Mn37.5Sn15 S. Arumugam, Subrata Ghosh, Arup Ghosh, U. Devarajan, M. Kannan, L. Govindaraj, Kalyan Mandal PII:

S0925-8388(17)31326-9

DOI:

10.1016/j.jallcom.2017.04.127

Reference:

JALCOM 41531

To appear in:

Journal of Alloys and Compounds

Received Date: 26 October 2016 Revised Date:

11 April 2017

Accepted Date: 13 April 2017

Please cite this article as: S. Arumugam, S. Ghosh, A. Ghosh, U. Devarajan, M. Kannan, L. Govindaraj, K. Mandal, Effect of hydrostatic pressure on the magnetic, exchange bias and magnetocaloric properties of Ni45.5Co2Mn37.5Sn15, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.04.127. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Effect of hydrostatic pressure on the magnetic, exchange bias and magnetocaloric properties of Ni45.5Co2Mn37.5Sn15 S. Arumugam1, Subrata Ghosh2, Arup Ghosh2,3*, U. Devarajan1,3, M. Kannan1, L. Govindaraj1 and Kalyan Mandal2 Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli 620024, India.

RI PT

1

2

Magnetism Laboratory, Department of Condensed Matter Physics and Material Sciences, S.N. Bose National Centre for Basic Sciences, Block-JD, Salt Lake, Kolkata 700106, India. Department of Physics, Indian Institute of Science Education and Research (IISER) Pune, Dr. Homi Bhabha Road, Pashan, Pune 411008, India.

M AN U

Abstract

SC

3

In this study, we report the effect of hydrostatic pressure (P) and magnetic field (H) on the magnetization, magnetocaloric effect and exchange bias in a Ni45.5Co2Mn37.5Sn15 Heusler alloy. At ambient pressure, the martensitic transition temperature (TM) shifts to lower

TE D

temperatures with a rate of dTM/dµ 0H ~ 3.29 K/T. On the other hand, TM increases rapidly to higher temperatures with dTM/dP ~ 31.90 K/GPa when hydrostatic pressure is applied. The peak value of magnetic entropy change due to change in magnetic field of 5 T is found to

EP

decrease with increasing pressure. Although, the relative cooling power (RCP) increases from ~189 Jkg-1 to ~ 204 Jkg-1 during cooling cycle, a significant drop in net RCP is obtained from

AC C

the measurements under heating cycle. The coercivity of the sample at a given temperature merely changes, but the exchange bias effect is improved by applying pressure.

Keywords: Magneto-structural transition; Magnetocaloric effect; Heusler alloys; Exchange bias; Hydrostatic pressure; Metamagnetic transition.

*Corresponding author’s E-mail: [email protected] and [email protected] 1. Introduction 1

ACCEPTED MANUSCRIPT Study of Co-doped Ni-Mn based Heusler alloys has already drawn immense attention to the researchers during the last decade due to its potential multifunctional properties like, magnetic shape memory effect (MSME) [1,2], large magnetocaloric effect (MCE) [1–10], magnetoresistance (MR) [11–13] and exchange bias (EB) effect [14–18]. The advantage of

RI PT

Co-doped over pristine similar Heusler alloys is that Co atoms work as a ferromagnetic (FM) activator in the system and enhance the magnetic activities even for better possible applications in magnetic refrigeration and memory devices [13,19,20]. Till date, plenty of

SC

such works have been carried out on Co-doped such alloys with Ga, Sn, In or Sb as a post transition agent to achieve better magnetic cooling [1,3,13,15,19,21–24]. For example: Mn-

M AN U

rich Mn2Ni1.64-xCoxSn0.36 alloys were studied by Han et al. and they reported the enhancement in MCE for optimal doping concentrations [3]. Other examples are like the observation of giant MCE near room temperature in Co substituted Ni-Mn-Sb Heusler alloys [4], role of Co and Fe in the MCE in Ni-Mn-Sn alloys [21], etc.

TE D

Despite of having all the above mentioned properties in Co doped such alloys, a very low percentage of doping is found to be effective in MCE [3,13,19]. In order to understand the fact, it is necessary to know about the structural properties of Heusler alloys [25]. Ni-Mn

EP

based off-stoichiometric FM Heusler alloys have cubic (L21) austenite structure which can

AC C

undergo a first order magneto-structural transition (FOMST) to a lower symmetric and magnetically weak tetragonal martensite phase on cooling depending upon the materials’ compositions [6,7]. Most of the magneto-coupled effects of these materials depend on the magnetic sensitivity across the FOMST, which starts to decrease for highly Co-doped Heusler alloys. There is an important MCE parameter called the relative cooling power (RCP), which measures the approximate amount of heat that can be extracted during a complete refrigeration cycle [26,27]. RCP in Co-doped materials decreases due to an increase

2

ACCEPTED MANUSCRIPT in magnetic hysteresis. Moreover, the observation of exchange bias in bulk polycrystalline Ni-Mn-Sb and Ni-Mn-Sn Heusler alloys made them promising in other ways [16–18,28]. There is an option to add the hydrostatic pressure (P) as stimuli to modify the electronic structure of a material which may lead to a significant change in the magnetic

RI PT

properties. The pressure dependence of the Curie temperature provides important information on FM system and is an object of intensive studies in experimental and theoretical fields [29– 33]. In our earlier work [13], we have reported the structural, magnetic, magnetocaloric and

SC

magneto-transport properties of Co-doped Ni-Co-Mn-Sn off-stoichiometric Heusler alloys under ambient pressure. We have found that the magnetic entropy change (∆SM) increased

M AN U

with increasing Co (replacing Ni). However, due to the appearance of larger field induced hysteresis, RCP decreased rapidly in higher doping concentrations. In the present work, we have investigated the effect of pressure on the structural phase transition, magnetic and magnetocaloric properties of Ni45.5Co2Mn37.5Sn15 sample, chosen

TE D

from our previous work [13]. The effect of magnetic field on FOMST was found to be opposite to that of hydrostatic pressure. The EB effect is improved with the applied pressure and most significantly, it has changed the nature of the temperature dependent plot of the

EP

same. The applied pressure does not affect the field induced metamagnetic transition

AC C

(FIMMT) (where the magnetization suddenly starts to increase nonlinearly in saturation region after a critical field) significantly. FIMMT is present during warming but it disappears during cooling. ∆SM is reduced but RCP enhanced due to the application of hydrostatic pressure.

2. Experimental details The material preparation technique, characterization and other ambient pressure studies such as isothermal magnetoresistance, magnetization on Ni45.5Co2Mn37.5Sn15 alloy are 3

ACCEPTED MANUSCRIPT already discussed elsewhere [13]. The magnetization measurements were performed at various hydrostatic pressures using a 9 Tesla Physical Property Measurement System (PPMS9T) -Vibrating Sample Magnetometer (VSM) (Quantum design, USA) module equipped with Cu-Be clamp type pressure cell with maximum pressure of 1 GPa [34]. The thermo magnetic

RI PT

data are recorded with VSM for both cooling and heating mode in the temperature range from 2 K to 320 K under the ambient and high pressures up to 0.9 GPa for Ni45.5Co2Mn37.5Sn15 alloy in presence of a constant magnetic field of 0.01 T and also under different magnetic

SC

fields (~ 1, 4, 7, 9 T). The isothermal magnetizations (M-H curves) are measured up to 5 T field at ambient and high pressures in different temperatures across the martensitic transition

M AN U

temperature (TM) during both the cooling and warming modes. In order to identify exchange bias properties in the sample, M-H curves were measured at different temperatures between 10 K and 130 K. 3. Results and discussion

TE D

3.1. Effect of magnetic field

The M-T measurements are carried out within the temperature range between 120 K

EP

and 320 K at different magnetic fields (0.01, 1, 4, 7 and 9 T) under ambient and 0.9 GPa hydrostatic pressure for Ni45.5Co2Mn37.5Sn15 (NCMS) and shown in Fig. 1(a and b). The

AC C

cooling (closed symbol) and warming (open symbol) curves are plotted in the same color for the same field M-T curves for the sake of clarity. A sudden drop in magnetization in cooling curves for various magnetic fields indicates the austenite to martensite transition. The exact values of characteristic transition temperatures (austenite start (As), austenite finish (Af), martensite start (Ms) and martensite finish (Mf)) by varying different magnetic fields at constant ambient (0 GPa) pressure are noted from the inflection point of the derivative of M (T) curves and summarized in Table 1. The temperatures below Mf, the magnetization 4

ACCEPTED MANUSCRIPT remains almost constant. Similarly, a sudden rise in the magnetization in warming curves at different magnetic fields is an indication of the forward transition from martensite to austenite. The region between martensite and austenite transition is represented as the thermal hysteresis (∆T) which confirms the first order nature of the transition. ∆T and magnetization

RI PT

are very low at low magnetic field (0.01 T) as compared to high magnetic field (9 T). While increasing the magnetic field, the first order transition initially shifts towards higher temperature up to 1 T field and then decreases to lower temperatures as the field is increased

SC

further. This gives the signature of field induced magneto-structural transition (FIMST). The sample might have large magnetocrystalline anisotropy and therefore, a higher value of field

M AN U

(>100 Oe) is necessary to completely unlock the system from its freezing state. This may results in the observed increase in TM up to 1 T field. Afterwards, the applied magnetic field tries to stabilize the magnetically more sensitive phase, which is here the cubic austenite and as a result, TM decreases with the increase in H beyond 1 T. TM and other characteristic

TE D

temperatures are tabulated in Table 1. In order to understand the effect of P and H on the FOMST, 0.9 GPa pressure is kept constant and the magnetic field then varied up to 9 T which is shown in Fig. 1(b) and these characteristic values are also tabulated in Table 2. It is found

AC C

GPa.

EP

that dTM/dH (~ -3.29 KT-1) at ambient pressure slightly decreases to -3.22 KT-1 under P = 0.9

3.2. Effect of hydrostatic pressure The M (T) curves are measured at selected values of pressure ( 0, 0.4 GPa, 0.7 GPa

and 0.9 GPa ) in presence of a constant magnetic field ( 0.01 T) within the temperature range between 150 K and 300 K, which are shown in Fig. 1(c). It reveals that the effect of pressure retains the first order transition and it is similar to the effect of magnetic field at ambient P. However, TM shifts towards room temperature with the rate of change as, dTM/dP ~ +31.9 5

ACCEPTED MANUSCRIPT K/GPa. The applied pressure decreases Mn-Mn separation which in turn favours antiferromagnetic (AFM) coupling and stabilizes martensite phase at higher temperature. Hence, we observed that magnetic and hydrostatic pressure provide opposite effect on the variation in first order transition. The pressure effect on TM and characteristic transformation

RI PT

temperatures are indicated in Table 3. A similar effect has been observed in Ni-Mn-Ga compounds [34]. 3.3. Isothermal magnetization

SC

The M-H measurements were carried out for NCMS around its FOMST in the field

M AN U

range of 0-5 T at selected values of pressure (0, 0.7 GPa, 0.9 GPa), spanning 150 K - 250 K and 190 K - 300 K with 5 K interval during cooling and warming respectively, shown in Fig. 2. The field sweeping is performed as follows: 0 → 5 T → 0. The FIMMT is present only in the warming cycle for all the applied pressure values in the temperature region from 190 K to 300 K as shown in Fig. 2(d-f). During cooling cycle, the FIMMT is absent which can be

TE D

explained by considering the effect of magnetic field and temperature on the FOMST of similar materials [35]. During warming cycle, the increase in both magnetic field and

EP

temperature results to the stabilization of magnetically more active cubic austenite phase. Therefore, across the structural transition the magnetization in the saturation region starts to

AC C

increase non-linearly above a critical field of ~3.5 T. In the cooling cycle, the temperature has the tendency to stabilize the martensite phase, whereas the magnetic field always tries to make the austenite phase stable. So the temperature induced irreversible transition opposes the field induced transition. This is why the magnetization does not increase non-linearly in the high field region during cooling. The hydrostatic pressure merely affects the FIMMT, but significantly diminishes the saturation magnetization in the austenite (MsatA) and martensite

6

ACCEPTED MANUSCRIPT (MsatM) phases as the applied pressure resists the moments from aligning along direction of magnetic field. 3.4. Exchange bias effect

RI PT

In order to understand the EB behavior in the present sample, the zero field cooled (ZFC) hysteresis loops (full looped M-H curves) are measured at different temperatures between 10 K and 130 K under ambient and 0.9 GPa pressure. Fig. 3(a) and 3(b) represents the ZFC magnetic hysteresis loops at 10 K and 80 K under both the applied pressures. The

SC

sample is first cooled to the targeted temperatures from 300 K in zero field and then the field

M AN U

sweeping is done as follows: 0→3T→0→-3T→0→3T (for the sake of clarity, only the region between -0.35 T and +0.35 T is shown in Fig. 3. The width of the hysteresis increases initially resulting higher coercivity (HC) as the temperature increases from 10 K to the EB blocking temperature (TEB ~ 80 K) and then starts to decrease. TEB is defined by the temperature above which the EB field almost vanishes in a material. As the temperature

TE D

increases, the thermal energy diminishes the interfacial exchange interaction between the FM and AFM sites, which in turn results in a decrease in EB field. Here we have observed the

EP

ZFC EB behavior at ambient as well as higher pressure. These results can be analyzed by calculating EB parameters like EB field (HE). The values of HE and HC are calculated using

AC C

HE = |(H1+ H2)|/2 and HC=|(H1-H2)|/2 respectively, where H1 denotes the field for zero magnetization during positive to reverse field sweeping and H2 denotes the same during opposite field sweeping. These values are shown in Fig. 3(c) and 3(d) for ambient and high P measurements. One can notice that HC remains almost independent of the hydrostatic pressure, whereas HE shows a small decrease in magnitude with the increase in P at 10 K. It can also be observe that the curvature of the temperature dependent HE curve switches from negative to positive as the pressure is applied. This signifies that the hydrostatic pressure 7

ACCEPTED MANUSCRIPT stabilizes the EB behavior. Here, the applied pressure compresses the unit cell of the sample and the Mn-Mn inter site separation decreases. This might leads to an enhancement in the AFM-FM interfacial coupling and also decreases in the volume of the FM domains. The cumulative result comes out as the increase in HE at 40 K and 80 K with applied high

RI PT

pressure whereas the same decreases at 10 K. 3.5. Magnetocaloric effect

The MCE of Ni45.5Co2Mn37.5Sn15 alloy has been estimated from the isothermal

SC

magnetization curves by calculating the ∆SM for various pressures using the Maxwell’s

M AN U

equation [6]

 ∂M (H , T )  ∆S M (T , ∆H ) = µ 0 ∫   dH ∂T H 0 H

(1)

where, M, T, H and µ 0 are respectively the magnetization of the sample, instantaneous

TE D

temperature, applied magnetic field and permeability of free space. ∆SM is calculated using the above equation by numerical integration of the isothermal M-H curves. However, it is always debatable to use the Maxwell’s equation to estimate ∆SM for a system with first order

EP

phase transition since the Maxwell’s relations are valid only when the entropy is a continuous

AC C

function of temperature and magnetic field [35]. For the similar systems, the first order transition is not completely ideal and hence, the changes in

( ∂M

∂T ) H is finite [36].

Therefore, one can still tentatively use eq. (1) by taking care of few parameters and process which is discussed in the next subsection of this article. ∆SM is plotted as a function of temperature at selected values of magnetic field in Fig. 4(a) and 4(b) for both cooling and warming cycles. The same parameter is also calculated for various magnetic fields at selected value of pressure applied for both heating and cooling protocol, which is shown in Fig. 4(c) and 4(d). The results are also given in Table 4. ∆SM monotonically increases with the increase 8

ACCEPTED MANUSCRIPT in ∆H due to motion of magnetic domain walls, twin boundary and the magnetic spin rotation. On the other hand, peak values of ∆SM for a particular ∆H decreases as the higher hydrostatic pressure is applied. This follows for both the cooling and warming cycles as well. As the pressure increases, it compresses the lattice stags and as a result, both the intra and

RI PT

inter site Mn-Mn separation decreases. This turns out to be a decrease in FM and increase in AFM interaction in the system. In addition to that, the pressurized sample finds more crystalline anisotropy which suppresses the total magnetization of the sample and makes the

SC

FOMST less sharp (decrease in dM/dT). All these are cumulatively responsible for the

M AN U

decrease in ∆SM. 3.6. Relative Cooling Power

RCP is one of the most important parameters to quantify MCE. The RCP is a measure of the amount of heat that can be transferred between the hot and cold sinks during one ideal

following equation [27]

TE D

refrigeration cycle and it is calculated from the temperature dependent ∆SM curves using the

RCP = ∆S M

max

× ∆TFWHM

(2)

EP

where, ∆SMMax be the peak value of ∆SM of a ∆SM-T curve plotted for a specific field change value and ∆TFWHM is the temperature window of the full width at half maxima (FWHM) of

AC C

the same ∆SM-T curve. Field dependence of RCP for the sample at different pressures in cooling and warming cycles is shown in Fig. 5. It is found that RCP increases almost linearly with the increase of fields for all pressure values under both the cooling and warming cycles. It is interesting to note that the RCP under cooling cycle increases with increasing the pressure, but the same decreases under warming cycle. The cooling mode is free from the FIMMT and the transition width is also large which causes such enhancement in RCP. While, for warming cycle, the FIMMT and decrease in ∆SMMax reduce the RCP as the pressure is 9

ACCEPTED MANUSCRIPT increased. In addition to that, this family of materials suffer from large hysteresis loss (HL) due to FIMMT. Therefore, it is necessary to subtract the average HL from RCP. The average HL under µ 0Hmax = 5 T due to the field induced hysteresis are found to be ~ 53.09, 39.8 and 40.93 J/kg respectively for ambient, 0.7 GPa and 0.9 GPa pressure which in turn minimizes

RI PT

the RCP during heating protocol to its net value as 147.04, 146.6 and 130.14 J/kg. In one of our earlier works [37], we have found that the measurement of MCE using Maxwell’s equation in warming cycle for Ni-Mn based Heusler alloys may lead to an overestimated

SC

outcome due to the appearance of FIMMT. But, cooling mode is free from such problems and

magnetocaloric applications. 4. Conclusion

M AN U

thus the outcome from the present study may advance similar materials for their

In summary, we have observed that the hydrostatic pressure and magnetic field can drastically change the transformation temperatures in Ni-Co-Mn-Sn alloys. For instance, the

TE D

first order magneto-structural transition of similar materials can be tuned by applying both the pressure and magnetic field as they influence the transition temperature oppositely. The

EP

exchange bias property of these materials can be enhanced by applying hydrostatic pressure. Although the magnetic entropy change decreases, the enhancement in relative cooling power

AC C

in the sample under higher pressure is very advantageous in the context of the application of similar materials to achieve potential magnetic cooling. Acknowledgements

One of the authors (S.G.) is thankful to Council of Scientific & Industrial Research (CSIR), India for providing him Junior Research Fellowship. Arup Ghosh is thankful to SERB, DST, Govt. of India for providing the financial support through National PostDoctoral Fellowship (PDF/2015/000599). Another author U.D. is grateful to acknowledge to 10

ACCEPTED MANUSCRIPT SERB- National Post-Doctoral Fellowship (PDF/2016/000412). The author S.A. wishes to thank DST (SERB, PURSE, FIST), DRDO (New Delhi), BRNS (Mumbai) and CEFIPRA (New Delhi).

[1]

RI PT

References K. Ito, W. Ito, R.Y. Umetsu, S. Tajima, H. Kawaura, R. Kainuma, K. Ishida, Scr. Mater. 61 (2009) 504–507. [2]

F. Chen, Y.X. Tong, B. Tian, L. Li, Y.F. Zheng, Y. Liu, J. Magn. Magn. Mater. 347

Z. Han, J. Chen, B. Qian, P. Zhang, X. Jiang, D. Wang, Y. Du, Scr. Mater. 66 (2012)

M AN U

[3]

SC

(2013) 72–74.

121–124. [4]

A.K. Nayak, K.G. Suresh, A.K. Nigam, J. Phys. D. Appl. Phys. 42 (2009) 35009.

[5]

S.E. Muthu, N.V.R. Rao, M.M. Raja, D.M.R. Kumar, D.M. Radheep, S. Arumugam, J. Phys. D. Appl. Phys. 43 (2010) 425002.

A. Planes, L. Mañosa, M. Acet, J. Phys. Condens. Matter 21 (2009) 1–29.

[7]

V.D. Buchelnikov, V. V Sokolovskiy, Phys. Met. Metallogr. 112 (2011) 633–665.

[8]

M. Kohl, V. Chernenko, D. Bourgault, J. Tillier, P. Courtois, X. Chaud, N. Caillault,

EP

TE D

[6]

L. Carbone, Phys. Procedia 10 (2010) 120–124. T. Krenke, E. Duman, M. Acet, E.F. Wassermann, X. Moya, L. Manosa, A. Planes,

AC C

[9]

Nat Mater 4 (2005) 450–454.

[10] J. Liu, T. Gottschall, K.P. Skokov, J.D. Moore, O. Gutfleisch, Nat Mater 11 (2012) 620–626.

[11] A.K. Nayak, K.G. Suresh, A.K. Nigam, Appl. Phys. Lett. 96 (2010) 2010–2013. [12] W. Ito, K. Ito, R.Y. Umetsu, R. Kainuma, K. Koyama, K. Watanabe, A. Fujita, K. Oikawa, K. Ishida, T. Kanomata, Appl. Phys. Lett. 92 (2008) 1–4. 11

ACCEPTED MANUSCRIPT [13] A. Ghosh, K. Mandal, Eur. Phys. J. B 579 (2013) 295–299. [14] S. Esakki Muthu, N. V. Rama Rao, D. V. Sridhara Rao, M. Manivel Raja, U. Devarajan, S. Arumugam, J. Appl. Phys. 110 (2011) 023904. [15] B. Wang, Y. Liu, Metals (Basel). 3 (2013) 69–76.

RI PT

[16] Z. Li, C. Jing, J. Chen, S. Yuan, S. Cao, J. Zhang, Appl. Phys. Lett. 91 (2007). [17] M. Khan, I. Dubenko, S. Stadler, N. Ali, J. Appl. Phys. 102 (2007).

[18] M. Khan, I. Dubenko, S. Stadler, N. Ali, Appl. Phys. Lett. 91 (2007).

SC

[19] A. Ghosh, K. Mandal, J. Alloys Compd. 579 (2013) 295–299.

[20] R.Y. Umetsu, A. Sheikh, W. Ito, B. Ouladdiaf, K.R.A. Ziebeck, T. Kanomata, R.

M AN U

Kainuma, Appl. Phys. Lett. 98 (2011).

[21] T. Krenke, E. Duman, M. Acet, X. Moya, L. Mañosa, A. Planes, J. Appl. Phys. 102 (2007).

[22] R.Y. Umetsu, A. Sheikh, W. Ito, B. Ouladdiaf, K.R.A. Ziebeck, T. Kanomata, R.

TE D

Kainuma, Appl. Phys. Lett. 98 (2011) 10–13.

[23] M. Pan, B. You, Y. Zhao, S. Wang, M. Lu, A. Hu, H. Zhai, S. Zhou, Phys. Lett. A 313 (2003) 442–447.

EP

[24] F. Chen, Y.-X. Tong, B. Tian, L. Li, Y.-F. Zheng, Rare Met. 33 (2014) 511–515.

AC C

[25] M. Khan, I. Dubenko, S. Stadler, N. Ali, J. Phys. Condens. Matter 16 (2004) 5259. [26] J.-H. Chen, N.M. Bruno, I. Karaman, Y. Huang, J. Li, J.H. Ross, J. Appl. Phys. 116 (2014).

[27] P. Gorria, J.L.S. Llamazares, P. Álvarez, M.J. Pérez, J.S. Marcos, J.A. Blanco, J. Phys. D. Appl. Phys. 41 (2008) 192003. [28] J. Nogués, I.K. Schuller, J. Magn. Magn. Mater. 192 (1999) 203–232. [29] S. Morán, C. Ederer, M. Fähnle, Phys. Rev. B 67 (2003) 12407. [30] H. Yamada, K. Terao, K. Kondo, T. Goto, J. Phys. Condens. Matter 14 (2002) 11785. 12

ACCEPTED MANUSCRIPT [31] H. Yamada, K. Fukamichi, T. Goto, Phys. Rev. B 65 (2001) 24413. [32] A. Kashyap, A.K. Solanki, T. Nautiyal, S. Auluck, Phys. Rev. B 52 (1995) 13471– 13474. [33] S. Wei, R. Duraj, R. Zach, M. Matsushita, A. Takahashi, H. Inoue, F. Ono, H. Maeta,

RI PT

A. Iwase, S. Endo, J. Phys. Condens. Matter 14 (2002) 11081.

[34] U. Devarajan, S. Esakki Muthu, S. Arumugam, S. Singh, S.R. Barman, J. Appl. Phys. 114 (2013).

SC

[35] M. Kataoka, T. Kanomata, R. Y. Umetsu, R. Kainuma, J. Magn. Magn. Mater. 361 (2014) 34.

M AN U

[36] A. Aryal, A. Quetz, S. Pandey, T. Samanta, I. Dubenko, M. Hill, D. Mazumdar, S. Stadler, N. Ali, J. Alloys Compd. 709 (2017) 142-146.

AC C

EP

TE D

[37] A. Ghosh, P. Sen, K. Mandal, J. Appl. Phys. 119 (2016) 183902.

13

ACCEPTED MANUSCRIPT Figure captions: Fig. 1. Temperature dependent magnetization (M-T curves) on warming and cooling at selected values of magnetic fields under (a) ambient pressure and (b) P = 0.9 GPa of Ni45.5Co2Mn37.5Sn15 alloy. (c) M-T curves on warming and cooling at different hydrostatic (arrows indicate the warming and cooling paths).

RI PT

pressures ( 0 GPa, 0.4 GPa, 0.7 GPa, 0.9 GPa) in presence of a magnetic field of 0.01 T

Fig. 2. Field dependence of magnetization (M-H curves) of Ni45.5Co2Mn37.5Sn15 alloy at different temperatures across the martensitic transition for selected values of hydrostatic

SC

pressure ( 0 GPa 0.7 GPa and 0.9 GPa ) during (a-c) cooling (d-f) warming cycle.

Fig. 3. Zero field cooled magnetic hysteresis loops measured at 10 K and 80 K for

M AN U

Ni45.5Co2Mn37.5Sn15 alloy under (a) ambient pressure and (b) P = 0.9 GPa. Temperature dependent exchange bias parameters of Ni45.5Co2Mn37.5Sn15 alloy at (c) ambient pressure and (d) P = 0.9 GPa.

Fig. 4. Magnetic entropy change as function of temperature of Ni45.5Co2Mn37.5Sn15 alloy at ambient pressure under different magnetic fields applied during (a) cooling and (b) warming cycle. Temperature dependent magnetic entropy change of Ni45.5Co2Mn37.5Sn15 alloy at

TE D

selected hydrostatic pressures (0 GPa, 0.7 GPa and 0.9 GPa) associated with a field change from 0 to 5T during (c) cooling and (d) warming cycle. Fig. 5. Field dependent relative cooling power (RCP) of Ni45.5Co2Mn37.5Sn15 alloy at various

AC C

cycle.

EP

hydrostatic pressures (0 GPa, 0.7 GPa and 0.9 GPa) during (a) cooling and (b) warming

14

ACCEPTED MANUSCRIPT Tables with caption: Table 1. Characteristic transition temperatures of Ni45.5Co2Mn37.5Sn15 at ambient pressure in presence of different applied magnetic fields. P = 0 GPa, Characterization transformations temperatures (K) Mf

As

Af

0.01

215

180

209

254

1

219

196

232

255

4

211

187

225

248

7

200

176

217

9

195

168

212

TA (K)

=(Ms+Mf)/2

=(As+Af)/2

198

232

208

244

199

237

SC

Ms

TM (K)

RI PT

H (T)

188

229

236

182

224

TE D

M AN U

241

Table 2. Characteristic transition temperatures of Ni45.5Co2Mn37.5Sn15 at 0.9 GPa pressure in presence of different applied magnetic fields.

H (T)

EP

P=0.9 GPa,

Characterization transformations temperatures (K)

AC C

Ms

Mf

As

Af

TM (K)

TA (K)

=(Ms+Mf)/2 =(As+Af)/2

0.01

245

209

239

281

227

260

1

249

222

258

283

236

271

4

238

214

250

277

226

264

7

232

202

241

267

217

254

9

223

197

236

263

210

250

15

ACCEPTED MANUSCRIPT Table 3. Characteristic transition temperatures of Ni45.5Co2Mn37.5Sn15 under different pressure applied.

215

180

209

254

0.4

220

190

219

271

0.7

232

202

236

277

0.9

245

209

239

281

TA (K) =(As+Af)/2

198

232

205

245

217

257

227

260

M AN U

SC

0

TM (K) =(Ms+Mf)/2

RI PT

P (GPa)

H = 0.01 T Characterization transformations temperatures (K) Ms Mf As Af

Table 4. Magnetic entropy changes of Ni45.5Co2Mn37.5Sn15 under different applied field and

TE D

pressure.

Value of ∆SM (J/kg K) for different field near TM

During cooling cycle

EP

Pressure applied (GPa)

During warming cycle

∆H = 5T

∆H = 1T

∆H = 5T

2.76

13.67

3.11

13.4

0.7

2.21

12.3

2.0

10.2

0.9

2.95

10.7

2.78

11.0

0

AC C

∆H = 1T

16

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Highlights of our work We report pressure effect on magnetocaloric effect in Ni45.5Co2Mn37.5Sn15 alloy.

•

Magnetic field and pressure oppositely affect the first order phase transition.

•

The exchange bias effect is found to be improved with the applied pressure.

•

Magnetocloric effect reduced due to applied pressure, but cooling power enhanced.

AC C

EP

TE D

M AN U

SC

RI PT

•