Evolution of Magnetic Glass on Partial Crystallization of a Bulk Metallic Glass: Tb36Sm20Al24Co20

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by  Archana Lakhani

Evolution of Magnetic Glass on Partial Crystallization of a Bulk Metallic Glass:
Tb Sm Al Co
36 20 24 20
Archana Lakhani*, A. Banerjee, and P. Chaddah
UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore-452001,India
J.Q. Wang and W.H Wang
Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
2 *[email protected]
1
0 Abstract. A comparative study on as cast and annealed rare earth bulk metallic glass (BMG)
2
withcomposition Tb36Sm20Al24Co20 hasbeencarriedoutbymagnetization measurements. Theas

n cast amorphoussample shows non-ergodicmagnetization but does not show thebehaviorexpected
a from magnetic glass. After annealing, the partially crystallized BMG shows this magnetic glass
J behavior. This is confirmed by the established measurement protocol of cooling and heating in

5 unequalfields(CHUF).
2
PACSnumbers: 61.43.Fs,75.47.Np,75.50.Lk

] Keywords: Bulk metallic glasses, Field induced transition in metals and alloys, spin glasses and magnetic
i
c glasses
s
-
l
r INTRODUCTION mosphere and then suck - cast into a Cu mold to get
t
m a cylindrical rod of 2 mm diameter. A small piece of
◦
. Structural glasses are disordered materials which lack this sample was crystallized by annealing at 450 C. The
at crystalline periodicity and are mechanically solids. Most amorphous and crystalline nature of the sample is con-
m metals crystallize on cooling, arranging their atoms into firmed by X-ray diffraction using Bruker (D8 Advance)
- aregularpatterncalledlattice,butifcrystallizationdoes X-raydiffractometerwithCuKαradiations. Magnetiza-
d notoccurandtheatomssettleinarandomarrangement, tion measurements were carried out using a commercial
n
the final form is a metallic glass[1]. The critical cooling 14T-VSM PPMS.
o
c rateismuchslowerforBMG’s,enablingmetglasssamples
[ of larger dimensions[2, 3].
RESULTS AND DISCUSSIONS
A similar kind of arrested kinetics of the first order
1
v magnetic transition from ferromagnetic (FM) to antifer-
5 romagnetic (AFM) or vice versa has been observed in The reported glass transition temperature (Tg), crys-
5 half doped Manganites and in various intermetallic al- tallization temperature (Tx), and the melting temper-
2 loys like doped CeFe2, Co doped Mn2Sb, FeRh and fer- ature (Tm) of the BMG Tb36Sm20Al24Co20 is 309◦C,
5 ◦ ◦
romagnetic shape memory alloys in recent years. These 383 C and 659 C respectively [3]. BMGs are partially
.
1 materialshavebeenexaminedthoroughlybyvariouspro- crystallized by isothermal annealing at a temperature in
0
tocols including the novelprotocolCHUF conceivedand the supercooled liquid region or by fast annealing just
2
developed to identify the magnetic glasses and its low above crystallization temperature [2]. This is known as
1
: temperature equilibrium state [4, 5]. The commonality partial devitrification of BMGs which gives rise to the
v
betweenthestructuralandmagneticglassisthearrested formation of composites or multi-phases. The magnetic
i
X kinetics resulting in the persistence of high temperature behavior is complex especially in RE based BMGs when
r state as the metastable state at low temperature. multiphases are present after tailoring them by differ-
a
In this manuscript, we highlight on the possibility ent heat treatments. In order to understand whether
of a rare-earth bulk metallic glass with composition the inhomogeneous structure arising from multi-phases
Tb36Sm20Al24Co20tobeamagneticglass. Wehavecom- can hinder the critical dynamics, we have performed the
paredthemagnetizationbehaviorofascastandannealed Zero Field cooled (ZFC) and Field cooled magnetization
specimen in order to find the correlation between struc- (FC)measurementsatvariousfieldsonascastaswellas
tural glass and magnetic glass. annealed sample.
Figure 1(a) shows ZFC and FC behavior of the M(T)
EXPERIMENTAL
measurements at 0.5T, 1T and 2T on as cast sample.
The bifurcation between the ZFC and FC curves is an
The as cast BMG-Tb36Sm20Al24Co20 sample is pre- indication of non-ergodicity. This temperature where
pared by arc melting the pure elements in an argon at- thebifurcationbetweentwocurvesbegin,decreaseswith
2
TbSmAlCo(As Cast) 57 onincreasingthewarmingfieldto2T.Ontheotherhand
80 21TT ∆M(emu/gm)455814 M(T)behavioronannealedsampleshowstwotransitions
M(emu/gm)4600 0.5T 450.4 0.8 T1(.K2) 1.6 2.0 iw(nHhWfieng)ucwroehoi2llie(nCgonfialyenlddonD(eH)t.CraT)nhisseithisiougndhwderehntehnfaaHnllCtihn≤emwHaaWgrnmaeitsniszghafiotiewoldnn
20 at low temperatures for H > H signifies the devit-
C W
[A]
0 rification of the magnetic glassy state and we note that
0 10 20 30 40 50 60 70
T(K) for H > H we have non-ergodic behavior below ∼
223050A2nTnealed at 4500C ∆M (emu/gm)6789 1te5mKpweCrhaetruereasWatfo∼r H20CK<. HW, it is observed at a higher
M(emu/gm)110505 01.5TT 50.5 1.0H(T)1.5 [B2].0 M(emu/gm)M(emu/gm)4567456700000000220011,,..TT3355,,TT1100TT 1144KK AAss ccMMaaeessttaassuurreedd iinn 11TT 0 0 0FF2310FF231 .TT0.TT0TTCCCC55TTCWCWTT____1111TTTTM(emu/gm)M(emu/gm)11122111222581425814 002121113355..TTTT0055TTTTTTTT 1155KK 3300KK MMeeaa44ss55uu00rrCCeedd AA iinnnnnn 11TT
0 50 100 150 200 250 300
99
T(K) 3300 00 [[AA]] 66 00 [[cc]]
FIG.1: (A-B):ZFCandFCMagnetizationw.r.tTemperature 2200 1100 2200 TT3300((KK)) 4400 5500 6600 00 1100 2200 33TT00((KK)) 4400 5500 6600
at0.5T,1and2TonascastandannealedTb36Sm20Al24Co20. 8822 112233..0022TTTTTT 1133KK MMeeaassAAuussrree ccddaa iissnntt 22TT 2288 1100TT 2211KK MMeeaa44ss55uu00rrCCee ddAA iinnnnnn 22 TT
8800 22TT 33TT 1133KK 2299KK
2266
increase in magnetic field suggesting the irreversibility mu/gm)mu/gm)77776868 11TT mu/gm)mu/gm)2244 22TT
process begins at lower temperature as field rises. The M(eM(e7744 00..55TT M(eM(e2222 0011..TT55TT
7722
difference in ZFC and FC magnetization at low tem- [[BB]]
7700 00 2200 00
perature is defined as the thermomagnetic irreversibil- 55 1100 1155 2200 2255 3300 00 55 1100 1155 2200 2255 3300 3355 4400 4455 5500
TT((KK)) TT((KK))
ity(∆M=MZFC@5 K−MFC@5 K)whichincreasesupto
1T and then decreases thereafter at 2T for as cast sam- FIG.2: (A-D):M(T)at1and2Taftercoolinginvariousfields
ple as shown in the inset of figure1(A). Similar type of markedonascastandannealedsampleofTb36Sm20Al24Co20.
non-ergodicbehavior and ∆M has been observedin spin
glasses. Figure 1(B) shows the ZFC and FC magnetiza-
tionbehaviorofthecrystallinecounterpartat0.5,1and Hence, our measurements show that the as cast amor-
2T which shows an antiferromagnetic transition (TC) at phous BMG sample does not become a magnetic glass
∼ 30K and it decreases to 29K at 2T. This FM-AFM whereas the annealed (partially crystallized) sample re-
transition is not seen in the as cast sample. Inset of sembles a magnetic glass.
figure1(B)showsthethermo-magneticirreversibilitybe-
havior which increases with field in contrary to the as
cast sample. ∆M rising with field has been observed in
magnetic glasses mentioned above.
REFERENCES
To validate the kinetically arrested state in the crys-
talline counter part we have performed the well known
protocolCHUFonascastaswellasonthepartiallycrys- [1] A. L.Greer, Science 267, 1947 (1995).
[2] A. Inoue,Acta mater. 48 (2000) 279-306.
tallized sample as shownin figure 2. Figure 2 (A and B)
[3] Q Luo, and W.H Wang, J. of Non Crystalline Solids 355
shows the temperature dependent magnetization at 1T
(2009) 759.
and2T after cooling invariousfields onthe ascastsam- [4] A. Banerjee et al., Sol. State Comm. 151 (2011) 971-975
ple. Magnetization measurements at 1T after cooling in and references therein.
0, 0.5,1, 2, 3, and 10T demonstrates the non-ergodic be- [5] A.BanerjeeetalJ.Phys.Cond.Matter21,(2009)026002
haviorofascastsamplebelow14K,whichreducesto13K ; arXiv : 0805.1514v1