CHUF and `unfreezing' (or de-arrest) of kinetic arrest in magnetic shape memory alloys

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by  P. Chaddah

CHUF and ‘unfreezing’ (or de-arrest) of kinetic arrest in magnetic shape memory
alloys
P. Chaddah and A. Banerjee
UGC-DAE Consortium for Scientific Research, University Campus,
Khandwa Road, Indore-452001, Madhya Pradesh, India.
CHUF (cooling and heating in unequal field) protocol allows establishing phase coexistence
through macroscopic measurements and enables distinguishing the metastable and stable phases
(amongst the coexisting phase fractions across a first order magnetic transition) of a glass-like ar-
2 restedstate(GLAS).Theobservationofkineticarrestinmagneticshapememoryalloyshasbecome
1 a very active area of research. We highlight recent CHUF measurements on these materials that
0 showbehavioursimilartothatreportedearlierinmanganitesandotherintermetallicalloys,empha-
2 sizingthegenerality. Themartensitictransitionprovidesanopportunitytostudyvariousproperties
n as theCHUF protocol enables tuningof phase fractions, and controlled devitrification, of GLAS.
a
J
Wehavenotedrecentlythatthekineticsofafirstorder phase was ferromagnetic, apply for a generic ‘magnetic
3
transition is dictated by the time required for the latent glass’. By similar arguments, the GLAS would show a

] heat to be extracted and, in addition to the well-known reentrant transition only for negative (HC - HW) when
i
c quenched metallic glasses, the kinetics of any first or- the high temperature phase was antiferromagnetic.
s der transition (including long-range-orderto long-range-
- Kainuma’s group has reported [12–16] measurements
l order transitions) could thus be arrested [1]. When a
r on Ni-Mn-In based alloys on cooling in various high
t firstordermagnetictransitioniskineticallyarrested,this
m magnetic fields, and warming in lower fields. In these
glass-like arrested state (GLAS) has been referred to as
studies, the low-temperature martensite phase has lower
.
t a ‘magnetic glass’ [2–11].
a magnetization, and the preceding statements for a high-
m temperature ferromagnetic phase apply. They observe
Phase-coexistence has been observed to persist in
- many half-doped manganites even at the lowest temper- the “unfreezing of the P+M coexisting state” [12] when
d warminginasmallfieldof0.05Tesla. Thisdevitrification
n ature. It has been shown that cooling in different values
observed in manganites with a charge-ordered ground
o of magnetic field may aid or prevent this kinetic arrest,
state [5, 7] has now been reproduced in detail, follow-
c and the coexisting phase fractionat low temperature, at
[ ing the CHUF protocol, in Ni-Mn-Sn based alloys for a
any measurement field H, can be tuned by cooling in an
4 Tesla warming field [17, 18]. For cooling fields greater
1 appropriatefieldandthenchangingthefieldisothermally
than 4 Tesla, devitrification is observed during warm-
v to H [5]. Cooling in some field may allow the first order
5 ing,showinganaustenitetomartensitetoaustenitereen-
transition to be completed and the equilibrium state to
7 trant transition. The CHUF protocol also provided the
be established,whilecoolinginaverydifferentfieldmay
5 addedconfirmationthatwhenthecoolingfieldissmaller
0 totally inhibit (or arrest) the transition. Since the first
than 4 Tesla the devitrificationis not observed. Further,
. order transition occurs over length scales of the corre-
1 with a fixed cooling field of 3 Tesla when the austenite
lation length, it was argued [3, 4] that the broadened
0
to martensite transition is completed only partly dur-
2 transition will be completed only partially for cooling
ing cooling, warming in fields lower than 3 Tesla shows
1 field lying between two values (H1 and H2) of magnetic
v: field. If the cooling field is below H1 the transition will devitrification. On the other hand, warming in fields
higher than 3 Tesla does not show devitrification. This
i be completed (totally arrested) if the high-temperature
X has been observed for both Mi-Mn-In based alloys [19]
phase was ferromagnetic (antiferromagnetic), and if the
r andforNi-Mn-Snbasedalloys[20]. Theanalogybetween
a cooling field is above H2 the transition will be totally
the magnetic shape memory alloys currently being stud-
arrested (completed) if the high-temperature phase was
ied, andthe manganitesstudied ingreatdetailearlier,is
ferromagnetic (antiferromagnetic). It was argued [3–5]
thus complete. The magnetic shape memory alloys ap-
that by using unequal and appropriately chosen cooling
peartocomplywiththepredictionsofthemagneticglass
andwarmingfields(HC andHW), de-arrest(ordevitrifi-
concept. The magnetic glass concept has been discussed
cation)ofthekineticallyarrestedGLAScouldbecaused,
for magnetic shape memory alloys by Sharma et al. [21]
and this de-arrest would be seen for only one sign of
also. But it has not been discussed in other extensive
(HC -HW). Furtherheatingwouldcausethisde-arrested
work on kinetic arrest of magnetic shape memory alloys
statetoundergothereversemagnetictransition,andthis
[12–16,22–24]. TheCHUFprotocolhasnotbeenusedin
cooling and heating in unequal field (CHUF) protocol
magneticshapememoryalloys,exceptinthe veryrecent
would show a reentrant transition. These phenomeno-
works [17–20].
logicalpredictions,wherethe reentranttransitionis seen
only for positive (HC - HW) when the high temperature The applicability of CHUF to establish the tuneabil-
2
ity of coexisting phase fractions with cooling field, and [7] P. Chaddah et al., Phys. Rev.B 77, 100402(R) (2008).
to establish the existence of a magnetic glass state has [8] A.Banerjeeetal.,J.Phys.: Condens.Matter21,026002
recently been also claimed in another family of materi- (2009).
[9] PallaviKushwahaelal.,Phys.Rev.B80,174413(2009).
als showing kinetic arrest, viz. doped cobaltites [25]. It
[10] V.G.Satheetal.,J.Phys.: Condens.Matter22,176002
is also being applied to more materials in the mangan-
(2010).
ite family [26–28]. The martensitic transition, however, [11] A.Lakhanietal., J.Phys.: Condens.Matter22,032101
offers interesting observationsthroughstructuralstudies (2010).
of, for example, nucleation and growth during devitrifi- [12] R.Y. Umetsu et al., Scr.Mater. 60, 25 (2009).
cation [29]. The presence of Sn in some of these mag- [13] W. Ito et al., Appl. Phys.Lett. 92, 021908 (2008).
netic shape memory alloys also affords the possibility of [14] W. Ito et al., Scr. Mater. 63, 73 (2010).
Mo¨ssbauer measurements of this devitrification process [15] Y. Lee et al., Scr. Mater. 64, 927 (2011).
[16] R. Y. Umetsu et al., J. Alloys and Compd. 509, 1389
under the CHUF protocol. There is a need to study the
(2011).
magnetic shape memory alloys in detail, as they may [17] A.Banerjeeetal.,SolidStateCommun.151,971(2011).
provide information on GLAS formed by arrest of first [18] A. Lakhani et al., Appl.Phys. Lett. 99, 242503 (2011).
order magnetic transitions between structurally ordered [19] A. Lakhani et al., AIP Conf. Proc. of DAESSP Sympo-
phases. sium (2011).
[20] A. Lakhani et al., (unpublished).
[21] V. K. Sharma et al., J. Phys.: Condens. Matter 22,
486007 (2010), and references therein.
[22] V. K. Karaca et al., Adv.Funct.Mat. 19, 983 (2009).
[23] W. Ito et al., Scr. Mater. 61, 504 (2009).
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