Coupled magnetostructural transformations in melt-spun
Ni55Mn19.6Ga25.4 ribbon: An electron spin resonance study
N. V. Rama Rao, R. Gopalan, J. Arout Chelvane, V. Chandrasekaran, and K. G. Suresh
Citation: J. Appl. Phys. 105, 123904 (2009); doi: 10.1063/1.3148863
View online: http://dx.doi.org/10.1063/1.3148863
View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v105/i12
Published by the American Institute of Physics.
Related Articles
Effects of nitrogen deficiency on the magnetostructural properties of antiperovskite manganese nitrides
J. Appl. Phys. 111, 07E314 (2012)
Structural and magnetic properties of Mn2+δTiSn
J. Appl. Phys. 111, 07B101 (2012)
Magnetic phase competition in Dy1−xYxMnO3
J. Appl. Phys. 111, 07D905 (2012)
Magnetic behavior of Mn-doped GaN (100) film from first-principles calculations
J. Appl. Phys. 111, 043907 (2012)
The magnetic Curie temperature and exchange coupling between cations in tetragonal spinel oxide
Mn2.5M0.5O4 (M=Co, Ni, Mn, Cr, and Mg) films
J. Appl. Phys. 111, 07A507 (2012)
Additional information on J. Appl. Phys.
Journal Homepage: http://jap.aip.org/
Journal Information: http://jap.aip.org/about/about_the_journal
Top downloads: http://jap.aip.org/features/most_downloaded
Information for Authors: http://jap.aip.org/authors
Downloaded 24 Feb 2012 to 14.139.97.76. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
JOURNAL OF APPLIED PHYSICS 105, 123904 共2009兲
Coupled magnetostructural transformations in melt-spun Ni55Mn19.6Ga25.4
ribbon: An electron spin resonance study
N. V. Rama Rao,1,2 R. Gopalan,1,a兲 J. Arout Chelvane,1 V. Chandrasekaran,1 and
K. G. Suresh2,b兲
1
Defence Metallurgical Research Laboratory, Hyderabad 500 058, India
Department of Physics, Indian Institute of Technology Bombay, Mumbai 400 076, India
2
共Received 27 February 2009; accepted 10 May 2009; published online 17 June 2009兲
Electron spin resonance study has been carried out on melt-spun ribbon of Ni55Mn19.6Ga25.4
exhibiting coupled magnetostructural transition. The correlation of electron spin resonance, thermal
and magnetic results permitted a clear distinction of various phases and their transformations. Both
structural and magnetic transitions coexist in the temperature range 300ⱕ T ⱕ 310 leading to four
different magnetic phases namely paramagnetic austenite, ferromagnetic austenite, paramagnetic
martensite, and ferromagnetic martensite. The sample exhibits a single paramagnetic austenite phase
above 310 K while it shows a ferromagnetic martensite phase below 260 K.
© 2009 American Institute of Physics. 关DOI: 10.1063/1.3148863兴
I. INTRODUCTION
Ferromagnetic Heusler alloys Ni– Mn– X 共X = Ga, Sn, In,
and Sb兲 form an important class of materials exhibiting ferromagnetic shape memory effect, giant magnetocaloric
共GMC兲
effect,
giant
magnetoresistance,
and
superelasticity.1–6 The multifunctional properties of Heusler
alloys have a wide range of applications in actuators, magnetic refrigerators, magnetomechanical transducers, switching devices, etc. In particular, Ni–Mn–Ga alloy generated
immense interest because of large magnetic field induced
strain as well as field induced entropy change. Heusler alloys
undergo a first order martensitic transition from a cubic 共austenite兲 phase to a tetragonal/orthorhombic 共martensitic兲
phase upon cooling. The martensitic transformation temperature 共Tm兲 and the Curie temperature 共TC兲 are composition
dependent. Tm and TC have been found to coexist in
Ni2+xMn1−xGa alloys over 0.18ⱕ x ⱕ 0.27, and this coupled
magnetostructural transformation leads to large GMC effect.7
The coupled magnetostructural transformations have been
characterized by magnetic, structural, and thermal
measurements.8,9 Although these measurements give an idea
about the transformation temperatures, a clear understanding
of the magnetic nature 共ferro-/para-兲 of the phases 共austenite/
martensite兲 around the magnetostructural transformation is
still elusive. Electron spin resonance 共ESR兲/ferromagnetic
resonance 共FMR兲 is particularly a suitable technique for such
a study, because it reveals the charge state, the site symmetry,
the g value, the internal magnetic fields and their distribution, the interactions among the ions and the lattice, the magnetic ordering, and the relaxation processes, etc. However,
there are only a few reports on the temperature and angular
dependence of FMR in Ni–Mn–Ga alloys either in single
crystal or thin film form.10–12
a兲
Present address: National Institute for Materials Science, 1-2-1 Sengen,
Tsukuba- 305 0047, Japan.
b兲
Author to whom correspondence should be addressed. Electronic mail:
suresh@phy.iitb.ac.in.
0021-8979/2009/105共12兲/123904/4/$25.00
In the present investigation, we have selected melt-spun
ribbon of Ni55Mn19.6Ga25.4 exhibiting coupled magnetostructural transformations and carried out magnetic, thermal, and
ESR measurements as a function of temperature. The assignment of ESR/FMR lines with majority phases and the associated magnetic and structural transformations are discussed
in detail.
II. EXPERIMENTAL DETAILS
The precursor ingot was prepared by arc-melting the
starting elements 共99.99% purity兲 under argon atmosphere.
Subsequently, the ingot was induction melted in a quartz tube
and melt-spun in vacuum, at a typical wheel surface speed of
17 m/s. The ribbons were annealed under high vacuum at
1075 K for 3 h and then quenched in water. Microstructure
and elemental compositions were investigated by using scanning electron microscopy 共Leo 440i兲 attached to an x-ray
energy dispersive spectroscopy 共EDS兲 setup. The crystal
structure was identified by x-ray diffraction 共XRD兲. Temperature dependence of a.c. magnetization 共333 Hz兲 was recorded on both heating and cooling using an a.c. susceptometer in the temperature range of 77–330 K at an applied field
of 0.5 Oe. The phase transformation temperatures between
the martensite and austenite phases were determined by differential scanning calorimetry 共DSC兲 共TA Q100兲 at a
cooling/heating rate of 20 K/min. FMR/ESR measurements
were carried out on a commercial VARIAN E-15 ESR spectrometer operating at 9.3 GHz at temperatures between 140–
380 K. During this measurement the magnetic field was applied along the plane of the ribbon.
III. RESULTS AND DISCUSSION
The room temperature XRD and microstructure 共figure
not shown兲 of the heat treated ribbon indicate that the sample
is formed in single phase with orthorhombic structure. EDS
analysis revealed a highly homogeneous chemical composition without any microchemical segregation and the uniform
composition was found to be Ni55Mn19.6Ga25.4. Figure 1共a兲
105, 123904-1
© 2009 American Institute of Physics
Downloaded 24 Feb 2012 to 14.139.97.76. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
123904-2
Rama Rao et al.
J. Appl. Phys. 105, 123904 共2009兲
FIG. 2. ESR/FMR spectra at different temperatures for Ni55Mn19.6Ga25.4
melt-spun ribbon.
FIG. 1. 共Color online兲 共a兲 DSC curves and 共b兲 a.c. magnetic susceptibility
during cooling and heating cycles for Ni55Mn19.6Ga25.4 melt-spun ribbon.
shows the DSC curve for Ni55Mn19.6Ga25.4 ribbon during
heating and cooling cycles. The phase transformation temperatures, namely, martensite start 共M s兲, martensite finish
共M f 兲, austenite start 共As兲, and austenite finish 共A f 兲 temperatures are found to be 306, 297, 300, and 312 K respectively.
The phase transformation and magnetic transition temperatures determined from the a.c. magnetic susceptibility 共␹-T兲
measurements are shown in Fig. 1共b兲. It can be seen from
␹-T curve that the heating curve does not coincide with the
cooling curve but exhibits a narrow thermal hysteresis which
is characteristic of a first order structural transformation. It is
also evident from Fig. 1共b兲 that ferromagnetic to paramagnetic transition nearly coincides with the martensitic transition. The fact that the values As = 300 K, A f = 312 K 共obtained from DSC兲, and TC = 311 K indicates that the
magnetic transition takes place just before the completion of
FIG. 3. 共Color online兲 Typical ESR/
FMR spectra with corresponding fit
共solid line兲 at different temperature regimes for Ni55Mn19.6Ga25.4 melt-spun
ribbon.
Downloaded 24 Feb 2012 to 14.139.97.76. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
123904-3
J. Appl. Phys. 105, 123904 共2009兲
Rama Rao et al.
structural transition 共A f 兲. The coexistence of the austenite
and martensite phases at magnetic transition leads to complex magnetic behavior in the ribbon. In order to distinctly
identify the magnetic nature of these phases and the related
transformations an ESR study was carried out.
Figure 2 shows a sequence of ESR spectra in the temperature range of 140–380 K. The temperature dependence
of line shape can be separated in four regions viz., 共i兲 at high
temperatures 共T ⬎ 310 K兲—one resonance with Dysonian
line shape, 共ii兲 in the intermediate temperature region 共300
ⱕ T ⱕ 310兲—four distinct resonances with Lorentzian line
shape, 共iii兲 in the region of intermediate temperature 共260
ⱕ T ⬍ 300兲—two distinct resonances with Lorentzian line
shape, and 共iv兲 at low temperatures 共T ⬍ 260兲—one resonance with Lorentzian line shape. Figure 3 shows a typical
spectrum in these temperature regions.
The variation of resonance fields 共Hres兲 as function of
temperature is displayed in Fig. 4共a兲. In the high temperature
regime 共T ⬎ 310 K兲 a single resonance line with Dysonian
line shape is observed. The weak temperature dependence of
Hres and the Dysonian line shape indicate a typical paramag-
neticlike behavior.13 Corroborating the above results with
thermal and magnetization studies, the observed Hres in the
high temperature regime corresponds to paramagnetic austenite 共PA兲 phase.
In the intermediate temperature range 共300ⱕ T ⱕ 310兲,
four distinct resonances with Lorentzian line shape is observed. In this temperature regime, both structural and magnetic transitions coexist, leading to different magnetic phases
such as PA, ferromagnetic austenite 共FM兲, paramagnetic
martensite 共PM兲, and ferromagnetic martensite 共FM兲.
Around the Curie temperature the ferromagnetic correlations
starts with a mixture of coexisting ferro-/paramagnetic
phases. As a result, the coexisting austenite and martensite
phases would contain ferromagnetic and paramagnetic components, leading to four different resonance lines. The Hres
around 680 kA/m correspond to austenite ferromagnetic
phase while the value around 635 kA/m corresponds to austenite paramagnetic phase. Similarly the Hres around 342 and
208 kA/m correspond to martensite ferromagnetic and martensite paramagnetic phases, respectively. It is reported that
the magnetization for martensite phase is higher than that of
austenite phase,14 and hence the lower Hres value is assigned
to the martensite phase. The above prediction is based on the
resonance condition considering the demagnetizing field effects, for example, in the form of a plate or ribbon with
magnetic field applied in its plane.15
In the temperature regime of 260ⱕ T ⬍ 300 K, the
mixed FM and austenite phases give rise to two distinct resonance lines. The increase in resonance field with decreasing
temperature is the characteristic of a ferromagnetic behavior.
Although the DSC and ␹-T measurements show austenite
start temperature at As = 300 K, the FMR signal reveals the
presence of austenite phase up to 260 K. This shows that the
microscopic variation in the spin environment determined by
local probelike FMR is more sensitive than bulk techniques
such as a.c. magnetization and DSC. In the low temperature
regime 共T ⬍ 260 K兲, the presence of single resonance is attributed to the FM phase. The variation of the resonance field
with temperature indicates a typical ferromagnetic metal.
From the above analysis, it is clear that the Ni55Mn19.6Ga25.4
ribbon exhibits a transition from FM to PA phase through a
complex coexisting phase region of FM and PM.
Figure 4共b兲 shows the temperature dependence of resonance linewidths 共⌬H兲. The ⌬H of the single phase martensitic region decreases gradually with increasing temperature
up to 260 K, following the saturation magnetization behavior
关inset of Fig. 4共b兲兴. Similarly in the paramagnetic region the
ESR linewidths exhibit a weak temperature dependence corroborating the magnetization results. However, in the intermediate temperature region a complex behavior is observed
owing to the presence of both structural and magnetic inhomogeneities.
IV. CONCLUSIONS
FIG. 4. 共Color online兲 共a兲 Variation of resonance fields 共Hres兲 and 共b兲 linewidths 共⌬H兲 as function of temperature for Ni55Mn19.6Ga25.4 melt-spun ribbon. Saturation magnetization as function of temperature is displayed in
inset 共b兲.
In conclusion, coupled magnetostructural transformation
in melt-spun ribbon of Ni55Mn19.6Ga25.4 was studied through
ESR/FMR and corroborated with the thermal and magnetic
data. The ESR/FMR results show a clear distinction of mag-
Downloaded 24 Feb 2012 to 14.139.97.76. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
123904-4
netic and structural inhomogeneities around the transformation. The variation in Hres and ⌬H with temperature gives
evidence for these inhomogeneities. The present study, therefore, confirms that ESR/FMR as local probe is more sensitive than the bulk magnetic and thermal measurements.
ACKNOWLEDGMENTS
This work was supported by Defense Research and Development Organization 共DRDO兲, India. The keen interest
shown by the Director, DMRL in this work is gratefully acknowledged. The authors would like to thank Dr. B. Majumdar for his help in carrying out melt spinning experiments.
1
K. Ullakko, J. K. Huang, C. Kanter, V. V. Kokorin, and R. C. O’Handley,
Appl. Phys. Lett. 69, 1966 共1996兲.
F. X. Hu, B. G. Shen, and J. R. Sun, Appl. Phys. Lett. 76, 3460 共2000兲.
3
T. Krenke, E. Duman, M. Acet, E. F. Wassermann, X. Moya, L. Mañosa,
and A. Planes, Nature Mater. 4, 450 共2005兲.
4
K. Oikawa, W. Ito, Y. Imano, Y. Sutou, R. Kainuma, K. Ishida, S. Okamoto, O. Kitakami, and T. Kanomata, Appl. Phys. Lett. 88, 122507
共2006兲.
2
J. Appl. Phys. 105, 123904 共2009兲
Rama Rao et al.
M. Khan, N. Ali, and S. Stadler, J. Appl. Phys. 101, 053919 共2007兲.
C. Biswas, R. Rawat, and S. R. Barman, Appl. Phys. Lett. 86, 202508
共2005兲.
7
A. N. Vasil’ev, A. D. Bozhko, I. E. Dikshtein, V. G. Shavrov, V. D.
Buchel’nikov, M. Matsumoto, S. Suzuki, T. Takagi, and J. Tani, Phys.
Rev. B 59, 1113 共1999兲.
8
V. V. Khovailo, T. Takagi, A. D. Bozhko, M. Matsumoto, J. Tani, and V.
G. Shavrov, J. Phys.: Condens. Matter 13, 9655 共2001兲.
9
V. V. Khovaylo, V. D. Buchel’nikov, R. Kainuma, V. V. Koledov, M.
Ohtsuka, V. G. Shavrov, T. Takagi, S. V. Taskaev, and A. N. Vasil’ev,
Phys. Rev. B 72, 224408 共2005兲.
10
V. G. Gavriljuk, A. Dobrinsky, B. D. Shanina, and S. P. Kolesnik, J. Phys.:
Condens. Matter 18, 7613 共2006兲.
11
J. Dubowik, I. Gościańska, Y. V. Kudryavtsev, Y. P. Lee, P. Sovák, and M.
Konĉ, Phys. Status Solidi C 3, 143 共2006兲.
12
S. I. Patil, D. Tan, S. E. Lofland, S. M. Bhagat, I. Takeuchi, O. Famodu, J.
C. Read, K.-S. Chang, C. Craciunescu, and M. Wuttig, Appl. Phys. Lett.
81, 1279 共2002兲.
13
M. J. M. Pires, A. Magnus, G. Carvalho, S. Gama, E. C. Da Silva, A.
Coelho, and A. M. Mansanares, Phys. Rev. B 72, 224435 共2005兲.
14
V. V. Khovailo, V. Novosad, T. Takagi, D. A. Filippov, R. Z. Levitin, and
A. N. Vasil’ev, Phys. Rev. B 70, 174413 共2004兲.
15
C. Kittel, Introduction to Solid State Physics, 5th ed. 共Wiley, New York,
1979兲.
5
6
Downloaded 24 Feb 2012 to 14.139.97.76. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions