Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$

0.8 MB·English

by  M. Ghorbani Zavareh

Direct measurements of the magnetocaloric effect in pulsed magnetic fields:
The example of the Heusler alloy Ni Mn In
50 35 15
M. Ghorbani Zavareh,1,2 C. Salazar Mej´ıa,3,a) A. K. Nayak,3 Y. Skourski,1 J. Wosnitza,1,2 C. Felser,3 and
M. Nicklas3
1)Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden,
Germany.
2)Institut fu¨r Festko¨rperphysik, TU Dresden, 01062, Dresden, Germany.
3)Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
5 (Dated: 20 January 2015)
1
0 We havestudiedthe magnetocaloriceffect(MCE)intheshape-memoryHeusleralloyNi50Mn35In15 bydirect
2 measurementsinpulsedmagneticfieldsupto6and20T.Theresultsin6Tarecomparedwithdataobtained
fromheat-capacityexperiments. WefindasaturationoftheinverseMCE,relatedtothefirst-ordermartensitic
n
a transition, with a maximum adiabatic temperature change of ∆Tad = −7 K at 250 K and a conventional
J field-dependent MCE near the second-order ferromagnetic transition in the austenitic phase. The pulsed

9 magnetic field data allow for an analysis of the temperature response of the sample to the magnetic field
1 on a time scale of ∼ 10 to 100 ms which is on the order of typical operation frequencies (10 to 100 Hz) of
magnetocaloric cooling devices. Our results disclose that in shape-memory alloys the different contributions
]
tothe MCEandhysteresiseffectsaroundthemartensitictransitionhavetobe carefullyconsideredforfuture
i
c cooling applications.
s
-
l PACS numbers: 75.30.Sg,75.40.Cx, 75.60.Ej
r
t
m
. Recently, tremendous efforts have been made to ies have been done by calculating the isothermal en-
t
a find alternative technologies to replace the conven- tropy change, ∆S , based on indirect methods, how-
iso
m
tional gas compression/expansion technique for cool- ever,forfirst-orderphasetransitionsadditionalconsider-
- ing applications.1,2 Higher efficiency cooling and ations should be applied.8 Direct measurements, besides
d
environmental-friendly magnetic refrigeration based on givingthe adiabatic temperature change,∆T , whichis
n ad
the magnetocaloric effect (MCE) have initiated inten- one of the important parameters for magnetic refrigera-
o
sive research activity. Besides its practical application, tion,arestraightforwardandclosertothe actualprocess
c
[ MCE studies can give an extra insight in the prop- used in applications. Non-destructive pulsed-field facil-

erties of the magnetic phase transitions. Among the ities have typical pulse lengths of 10 to a few 100 ms,
1
most promising materials, Heusler-type Ni-Mn-In mag- which match the targeted operation frequency of mag-
v
0 netic shape-memory alloys are attractive candidates for neticrefrigerators,10-100Hz.9 Besidesextendingtheac-
3 bothfundamentalresearchandapplication. Thesealloys cessiblemagnetic fieldrangeandgoingbeyond50 T,the
4 have been shown to exhibit diverse functional proper- shortpulsedurationprovidesnearlyadiabaticconditions
4 ties such as shape memory,3,4 magnetic superelasticity,5 during the measurement. Thus, direct MCE measure-
0 magnetocaloric,6 and barocaloric effect,7 which origi- ments in pulsed magnetic fields provide the opportunity
.
1 nate from magnetoelastic couplings. Ni50Mn35In15 ex- to investigate the dynamics of the MCE in a suitable
0 hibits on cooling a paramagnetic to ferromagnetic tran- frequency range. In this work, we study the MCE in a
5 sition around 315 K, followed by a first-order struc- Ni Mn In sample by direct magnetocaloric measure-
50 35 15
1
tural transition from a cubic high-temperature phase to mentsinpulsedmagneticfieldsandbyanalyzingspecific-
:
v a low-temperature monoclinic phase around 246 K, the heat data taken in static magnetic fields.
i so-called martensitic transition. A conventional MCE
X Polycrystalline ingots of Ni Mn In were obtained
is observed around the ferromagnetic transition in the 50 35 15
r byarc-meltingstoichiometricamountsoftheconstituent
a austenitic phase. Here, an increase in the sample tem-
elements under argon atmosphere. The ingots were
peratureisobserveduponapplicationofamagneticfield
remelted several times to assure a high homogeneity.
in adiabatic conditions. Additionally, an inverse MCE
Subsequently they were encapsulated in a quartz am-
is present around the martensitic first-order transition
◦
poule under argon atmosphere and annealed at 800 C
leading to a decrease in the sample temperature with
for2handthenquenchedinice water. Thehighquality
increasing field. Due to the first-order character of the
of the samples was confirmed by powder X-ray diffrac-
latter transition, hysteresis losses and fatigue are criti-
tion. Magnetization and heat-capacity measurements
cal issues on the search of suitable materials for mag-
werecarriedoutinaphysicalpropertymeasurementsys-
netocaloric cooling devices. So far, most MCE stud-
tem (Quantum Design). Direct measurements of ∆T
ad
were performed in a home-built experimental setup in
pulsed magnetic fields at the Dresden High Magnetic
a)Electronicmail: [email protected] FieldLaboratory(HLD).Thetemperaturechangeofthe
2
sample was monitored by a Copper-Constantanthermo-
couple. The thermocouple was squeezed between two
100
piecesofthe sampletooptimizethe thermalcontactand
reduce the heat losses. The target temperature was ap-
80
proachedwiththehelpofalocalheater. AresistiveCer- )
g
noxthermometer wasutilized to determine the reference u/ 60
m
temperature. e
TheinsetofFig.1showstemperature-dependentmag- M ( 40
netization curves, M(T), of Ni50Mn35In15 measured at 20 u/g)18000 5 T
0.1 and 5 T, following FC (field cooled) and FH (field- m 60
e
cooled heating) protocols. The ferromagnetic transition 0 150 K 200 K M ( 2400
oftheausteniticphasetakesplaceatT ≈315K,andthe 210 K 230 K 0 0.1 T
C 250 K 120 180 240 300
martensitictransitionfromthe austenitic to the marten- -20 T (K)
sitic phase is on cooling observed at TM ≈ 246 K and 0 2 4 6 8 10 12 14
on heating around TA ≈257 K. The applied field of 5 T 0H (T)
shifts the martensitic transition temperature by about -
FIG. 1. Isothermal magnetization data measured in mag-
7K,whichindicatesthatthemagneticfieldstabilizesthe
netic fields up to 14 T for different temperatures below TA.
austenitic phase. The M(H)data inFig. 1 indicate that
Each measurement was preceded by heating up the sample
it is possible to induce the reverse martensitic transition
to the fully austenitic state and then cooling down to the
alsobyapplicationofamagneticfield,at150Kafieldof
completely martensitic state (100 K) before approaching the
14 T is sufficient to observe a completed transition. For measurement temperature. The inset shows FC (circles) and
each M(H) measurement the sample was cooled down FH(triangles) magnetization datafor0.1 T(closed symbols)
from the 350 K (austenitic phase) to 100 K (complete and 5 T (open symbols).
martensitic phase) in zero field and then heated up to
the target temperature of the experiment. By this pro-
tocol we assure that the sample is always in the same,
fully martensitic, initial state and that we can exclude 6
6
any influence of hysteresis effects on the results. At
4
150 K, we determined from the inflexion point in M(H) 300K
a critical field of H ≈ 13 T for inducing the transition 2 340K
from the martensitiAc to the austenitic state. When the K) 4 T)
fitoeltdheismreamrtoenvesidticagsataint,e.thNeotsea,mfoprleteims ptrearnastfuorremsecdlosbeactko t (T-ad20 200 K 223400KK H (
the transition at TA part of the sample remains in the -4 250K 2
austenitic phase after removing the magnetic field. We
observe a hysteresis of 2−3 T between the criticalfields -6 255K

uponincreasinganddecreasingthemagneticfield. Upon H=6 T
0
increasing the temperature toward TA the critical field, 12 K) 0 0 H= -20 T 20
HA(T), decreases. 8 300K t T (-ad3 a0veHra=g e20 T
The MCE, in this case the adiabatic temperature 15
fmcohreatnshegoleed,cst∆.edTFaitgdeu,mrwepae2sramshteuoarwseussrtrehedceobtryidmebdeotddheupdrieinrnegdceatnpacpnelsdic∆aintTdioaitnrde(cott)f t (K)Tad04 3401K50K -60.02 0t .(0s4) 0.0610 H (T)
apulsedfieldof6(top)and20T(bottom)togetherwith 230K 240K
thecorrespondingpulseprofile. Forpulsed-fieldmeasure- -4 200K 5
250K
ments at temperatures below the martensitic first-order
255K
transitionthesamplewascooleddownfrom350to100K -8 H=20 T
0
inzerofieldandthenheateduptothetargettemperature 0 0.05 0.10 0.15 0.20
as in the case of the M(H) measurements. Note, the lit- t (s)
tlebumpsobservedatthebeginningofthe∆Tt (t)curve
ad FIG. 2. Time dependences of the adiabatic temperature
inthe 20T experimentsarecontributionsfromthe mag-
change at 6 T (top) and 20 T (bottom), measured in pulsed
netization change in the sample. The small open loops
magnetic fields following the protocol described in the text.
in the thermocouple wires act like magnetization pick- Thefieldprofileisalsoindicated(rightaxis). Theinsetshows
up coils and detect the metamagnetic transition of the ∆Tatd(t) with pulsed fields of -20 T and 20 T at 240 K and
sample. The inset of Fig. 2 exemplifies how a reversalof theaverage of thetwo.
the field polarity affects the sign and magnitude of the
bump, confirming that it is not related to the MCE re-
sponse. To minimize this effect at all temperatures two
3
curvestakenonapositiveandanegativefieldpulseshave
been averaged. 12
1200
TCA≈ro3u1n5dKth,ewCeuorbiseetrevmeapecroantvuernetiinontahleMauCsEteansiteicxppehcatseed, 180 C (J/kg K)800 06 TT
(see the data at 300 and 340 K in Fig. 2). As the field is 6 400
appliedthemagneticmomentsintheaustenitefullyalign (K) 4 00 70 140 210 280 350
with the field and the magnetic entropy decreases. Since ad2 T(K)
T
themeasurementisperformedadiabatically,thedecrease
0
inthemagneticentropyiscompensatedbyanincreaseof
-2
lattice entropyleading to an increasein the temperature
of the sample. Furthermore, the effect is reversible, i.e., -4 6 T (heat capacity)
6 T (pulsed field)
after the magnetic pulse the sample reaches again the -6
20 T (pulsed field)
starting temperature. We point out that the position of -8
the maximumofthe pulseroughlycoincideswiththatof 150 200 250 300 350
the maximum in ∆Tt (t). T (K)
ad
On the other hand, the ∆Tatd(t) data at temperatures FIG. 3. The adiabatic temperature change, ∆Tad, as a func-
below the martensitic transition show a completely dif- tion of temperature obtained from heat-capacity data in a
ferentbehavior. Whenthefieldisapplied,thestructural fieldof6Tandmagnetocaloricmeasurementsinpulsedfields
transformation is induced and completed for all temper- of6and20T.Theinsetdisplaysthetemperaturedependence
aturesasshowninFig.2(withtheexceptionofthemea- of the specific heat at 0 and 6 T.
surementat200Kinthe 6T fieldrange). Thistransfor-
mation involves a positive entropy change, which leads,
in an adiabatically conducted experiment, to a negative
temperaturechange(inverseMCE),∆Tstr <0. Further- of the sample transforms back and, therefore, a smaller
ad
more, the structural transformationinvolves a change in change in temperature is observed in the down sweep
the magnetic state of the sample. The magnetizationin- compared to the up sweep. As a result, the final tem-
creasesinvolvinganegativeentropychange(conventional perature of the sample is lower than the initial one. In
MCE) corresponding to a positive temperature change, particular,at 255 K the temperature of the sample after
∆Tmag > 0. Thereby, the structural contribution works the field pulse remains below the starting temperature,
ad
against the magnetic contribution to the total MCE. As consequently,the sample does not transformback to the
the structuralcontributionis dominantfortemperatures martensite and no further heating is observed.
closetothemartensitictransition,aninverseMCEisob- Additionally to the MCE experiments in pulsed mag-
served, i.e., the sample cools down upon application of neticfields,wecarriedoutspecific-heatmeasurementsin
the magnetic field, ∆T =∆Tstr+∆Tmag <0.6 More- zerofieldandinanappliedfieldof6T.Forthemeasure-
ad ad ad
over,close to T the inverseeffect is irreversibleand the mentinmagneticfieldthesamplewascooledinzerofield
A
sample doesnotrecoverthe initialtemperatureafter the from the austenitic phase down to 2 K and the specific
magnetic field is removed and the maximum of the field heat was recorded on heating from 2 to 380 K. At the
profile does not coincide with the minimum in ∆Tt (t). first-order martensitic transition we carefully analyzed
ad
For all temperatures (except for 200 K and 6 T) the the slope of the temperature profile of a long heat pulse
applied magnetic field is large enough to induce and ob- to obtain the heat capacity.12 This procedure avoids an
serve a complete reverse martensitic transition (see Fig. underestimation of the heat capacity due to the latent
1). Thus, a pure austenitic state is reachedatthe endof heatatthe first-orderphasetransition.12,13 Thespecific-
the field-up sweep. As we mentioned previously, a hys- heatdataarepresentedintheinsetofFig.3. Fromthese
teresisof2−3Tispresentbetweentheinducedtransition results we calculated the temperature dependence of the
in the up and down sweep. Henceforth, as the magnetic total entropy for 0 and 6 T and subsequently the adi-
field is reduced again, we first observe a conventional abatic temperature change, ∆Tad. In the calculations
MCE due to the change of the magnetic entropy in the we have used the thermodynamic relations S(T)HI ≈
T T
ferromagnetic austenitic phase and the sample contin- R0 [C(T)HI/T]dT, S(T)HF ≈ R0 [C(T)HF/T]dT, and
ues to cool down further.6,10,11 As the field continues to ∆T (T) ≈ [T(S) − T(S) ] where H and
ad ∆H HF HI S I
decrease, the sample transforms back to the martensitic H indicate the initial and final magnetic field values,
F
phaseatthe criticalfieldofthe field-inducedmartensitic respectively.14 ∆T (T) obtained from the heat-capacity
ad
transition leading to a negative change of the structural data is presented in Fig. 3 together with the results of
entropy. As a consequence the sample starts to heat up the direct measurements. We note that due to the finite
again, ∆Tstr > 0. Depending on the temperature the response time of the thermocouple and the pick-up of a
ad
materialeitherrecoversthemartensiticphasecompletely magnetic signal due to the change in magnetization at
(see for instance curve at 230 K with field pulse of 6 T), the metamagnetic transition, it is not possible to trace
oramixedmartensitic/austeniticstateisestablished(see the time (field) dependence of ∆Tt precisely, only the
ad
the data at 240 and 250 K). In the latter case, only part maximum/minimumin∆Tt (t)iswelldefinedandthose
ad
4
values are plotted as ∆T in Fig. 3. We find, as ex-
ad
6
pected, an inverseMCE in the regionbelow the marten-
sitic transition and a conventional MCE around the fer- 4 u/g)10800 20
romagnetic transition of the austenitic phase, i.e., in an em 60
adiabaticenvironmentthesamplecoolsdownandwarms 2 M ( 40 15
uitmhpep, oMrerstCapEnectjtufivesateltbyu,erlueo,pwownthhiiecnhcmrweaarestiewnngasnittthicettomrapanogsinintetitoioncusfitaetilusdr.tahAtaents t T (K)ad0 200 0 2 4 6 T8=25100 K12 14 H (T)
0H (T) 10
alreadyinsmallmagnetic fields. ∆T reachesavalueof -2
ad
around -7 K at 6 T which does not change up to 20 T
-4
anymore. With a field change of 20 T, ∆Tad only dis- 5
plays a broader peak, since the reverse martensitic tran-
-6 pulse 1
sition can be induced also at lower temperatures. Our 0 H=20 T pulse 2
findings confirm that the inverse MCE due to the first- 0
0 0.05 0.10 0.15 0.20
order martensitic transition is limited by the latent heat
t (s)
of the transition.15 We note that the martensitic tran-
sition can be induced by a field of 20 T even at 4 K.16 FIG. 4. Time dependence of ∆Tatd measured at 250 K for a
magnetic-field pulse of 20 T. The initial curve (black circles)
With increasing temperature this critical field decreases
wasmeasuredfollowing thestandardprotocolasdiscussedin
andfor150Kthetransitionisalreadycompletedat14T,
text) and the second curve (red diamonds) was taken 1 hour
as indicated in Fig. 1. However, the MCE measured at
afterthefirstpulse. Thefieldprofileisalsoshown(rightaxis).
this temperature is only 20% of the maximum value at TheinsetshowsthecorrespondingM(H)curvesfollowingthe
250K.Thisbehaviorisrelatedtothe decreaseinthe en- same protocol.
tropychangeatthe structuraltransitionwithdecreasing
temperature.17
Around the second-order ferromagnetic transition in
the austenitic phase (TC ≈ 315 K) we find a good tocol as mentioned above. Figure 4 displays the results
agreement between the results obtained from the heat at250Kfor∆Tt (t)andM(H)(inset). TheM(H)data
ad
capacity and from the MCE measurements in pulsed indicatethatpulse1inducesthereversemartensitictran-
fields,buttherearedistinctdiscrepanciesbelowthefirst- sition and that the sample stays in the austenitic phase.
order martensitic transition. At temperatures just be- After 1 hour, only a small part of the sample has trans-
low the martensitic transition the minimum in the time- formedbacktothe martensiticphase. Thus,theentropy
dependedtemperaturechange,∆Tt (t),isobservedfora change due to the second pulse is much smaller and the
ad
magnetic field beyond the pulse maximum on the down maximum temperature change of the sample is less than
sweep. This maximum value in |∆Tt (t)| corresponds, 1/2 of that observed in the first pulse, |∆T | ≈ 6 K.
ad ad
therefore,notonly to the MCEas itis generallydefined. This observation is consistent with the M(H) data ob-
As we have discussed before, at these temperatures an tainedduringthesecondpulse,i.e.,onlypartofthesam-
inverse MCE is observed, i.e., the sample cools down ple is in the martensitic state and can still transform to
due to a dominant structural contribution (∆Tstr < 0 the austenitic phase. Furthermore,∆Tt (t) stays almost
ad ad
and ∆Tamdag > 0). This is the value of ∆Tad obtained constant after the initial decrease; the temperature re-
by the specific-heat experiments in static fields, but in laxes only very slowly towardsthe starting temperature.
case of the pulsed-field experiments decreasing the mag- This behavior hampers the use of shape-memory alloys
netic field leads to a further cooling of the sample, since in possible applications since to have a maximum cool-
∆Tmag < 0 and, initially, ∆Tstr ≈ 0. Only once the ing effect the sample needs to be brought to the initial
ad ad
field-induced structural transition takes place upon fur- conditions before each cooling cycle.
ther lowering the magnetic field, ∆Tstr provides a posi-
ad In summary, we have investigated the MCE in the
tive contribution to ∆Tt (t).
ad shape-memory Heusler alloy Ni50Mn35In15 by direct
The observed irreversibility in the MCE is expected magnetocaloric measurements in pulsed magnetic fields
in shape-memory Heusler materials.10,15 It originates andbyheat-capacityexperimentsinconstantfields. The
from the thermal/magnetic hysteresis at the first-order conventional MCE around the Curie temperature in the
martensitic phase transition. Therefore, field cycling or austenitic phase exhibits a strong magnetic-field depen-
repeatedmeasurementsatthesametemperaturewithout dence, for a field change of 20 T we find a maximum
consideringthemagneticandthermalhistoryofthesam- ∆T ≈ 11 K. In this region of the phase diagram we
ad
ple leadtodifferentresultsinthe MCE.Tostudy thein- do not find any hysteresis or irreversible behavior in the
fluenceoftheirreversibilityofthetransitionontheMCE magnetocaloric experiments in pulsed-magnetic fields.
for temperatures close to T , we have measured M and Furthermore,∆T isinagoodagreementwiththe data
A ad
∆Tt in two subsequent magnetic field sweeps. The sec- from heat capacity. This changes below the marten-
ad
ond pulse was appliedafter waiting 1 hour after the first sitic phasetransition. Here,weobserveaninverseMCE,
pulse, which was performed following our standard pro- which originates from structural and magnetic contribu-
5
tions. Inthedirectmagnetocaloricexperimentswefinda 5T. Krenke, E. Duman, M. Acet, E. F. Wassermann, X. Moya,
saturating MCE with a maximum negative temperature L.Man˜osa,A.Planes,E.SuardandB.Ouladdiaf,Phys.Rev.B
changeof∆T =−7K.Thisvalueissignificantlylarger 75,104414 (2007).
ad 6J. Liu, T. Gottschall, K. P. Skokov, J. D. Moore, and O. Gut-
than the results of the specific-heat analysis. The cause
fleisch,Nat.Mater.11,620(2012).
for this lies in the hysteresis observed at the martensitic 7L.Man˜osa, D. Gonzalez-Alonso, A.Planes, E.Bonnot, M.Bar-
phase transition which leads to a strongly irreversible rio,J.Tamarit,S.AksoyandM.Acet,Nat.Mater.9,478(2010).
time dependence of ∆Tt below the martensitic phase 8R.Niemann,O.Heczko,L.SchultzandS.Fa¨hler,Int.J.Refrig.
transition. This irreversiabdle behavior has to be carefully 37,281(2014).
9M.D.Kuzmin,Appl.Phys.Lett. 90,251916(2007).
takenintoconsiderationforusingshape-memoryHeusler
10V. V. Khovaylo, K. P. Skokov, O. Gutfleisch, H. Miki, R.
alloys in magnetocaloric-cooling applications, especially, KainumaandT.Kanomata,Appl.Phys.Lett.97,052503(2010).
sincethelengthofthemagneticfieldpulseiscomparable 11I.Titov,M.Acet, M.Farle,D.Gonzalez-Alonso, L.Man˜osa, A.
to the inverse of useful operation frequencies of cooling PlanesandT.Krenke,J.Appl.Phys.112,073914(2012).
12J. C. Lashley, M. F. Hundley, A. Migliori, J. L. Sarrao, P. G.
devices.
Pagliuso, T. W. Darling, M. Jaime, J. C. Cooley, W. L. Hults,
We acknowledge the support of the HLD at HZDR,
L. Morales, D. J. Thoma, J. L. Smith, J. Boerio-Goates, B. F.
member of the European Magnetic Field Laboratory Woodfield,G.R.Stewart,R.A.Fisher,andN.E.,PhillipsCryo-
(EMFL). This work was financially supported by the genics43,369(2003).
ERC Advanced Grant (291472)”Idea Heusler.” 13V.Hardy,Y.Br´eard,andC.Martin,J.Phys.: Condens.Matter
21,075403 (2009).
1C. Zimm, A. Jastrab, A. Sternberg, V. K. Pecharsky, K. A. 14V.K.PecharskyandK.A.Gschneidner, J.Appl.Phys.86,565
Gschneidner, M. Osborne and I. Anderson, Adv. Cryog. Eng. (1999).
43,1759(1998) 15B. Emre, S. Yuce, E. Stern-Taulats, A. Planes, S. Fabbrici, F.
2K. A. Gschneidner, V. K. Pecharsky and A. O. Tsokol, Rep. AlbertiniandL.Man˜osa,J.Appl.Phys.113,213905(2013).
Prog.Phys.68,1479(2005). 16A. K. Nayak, C. Salazar Mej´ıa, S. W. D´Souza, S. Chadov, Y.
3R.Kainuma,Y.Imano,W.Ito,Y.Sutou,H.Morito,S.Okamoto, Skourski,C.Felser,andM.Nicklas,Phys.Rev.B.90,220408(R)
O.Kitakami,K.Oikawa,A.Fujita,T.KanomataandK.Ishida, (2014).
Nature439,957(2006). 17C. Salazar Mej´ıa, M. Ghorbani Zavareh, A. K. Nayak, Y. Sk-
4A. Planes, L. Man˜osa and M. Acet, J. Phys.: Condens. Matter ourski,J.Wosnitza,C.Felser,andM.Nicklas,acceptedforpub-
21,233201(2009). lication.