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Giant elastocaloric effect in FeRh alloy
Physics Letters A 171 (1992) 234-236 North-Holland
PHYSICS LETTERS A
Giant elastocaloric effect in FeRh alloy S.A. Nikitin a, G. Myalikgulyev b, M.P. A n n a o r a z o v a, A.L. T y u r i n b, R.W. M y n d y e v b a n d S.A. Akopyan b • Department of Physics, Moscow State University, 119899 Moscow, Russian Federation b Department of Physics, Turkmen State University, 744014 Ashkhabad, Turkmenistan Received 31 August 1992; accepted for publication 10 September 1992 Communicated by V.M. Asranovich
The elastocaloric effect, the electrical resistivity and the thermal expansion have been investigated in a quenched sample of Fe49Rhsl alloy. The giant negative temperature change, resulting from a tensile stress of 529 MN/m 2 applied to the sample, is found to be 5.17 IC Using the Clapeyron-Clausius equation, the entropy jump and the anti.ferromagnetism-ferromagnetism transformation latent heat have been determined, the transformation being induced by the tensile stress applied to this alloy.
1. Introduction The thermal expansion and the thermal stress effects upon the temperature of transformation from the antiferromagnetic state to the ferromagnetic state (AF-F) were investigated in refs. [1,2]. The numerical estimates, obtained by the use of these resuits, and the specific heat data [ 3 ] have established that the temperature of FeRh alloy decreases by 1517 during the AF-F transition, induced by a tensile stress in adiabatic conditions. Furthermore, a giant negative magnetocaloric effect ( 13 K) was found [4 ] in a quenched Fe49Rhs'~ sample under magnetic field induction near 2 T. In order to gain additional information on the thermodynamic features of the AFF transition in the Fe-Rh system, it is of interest to carry out measurements on the elastocaloric effect for samples of the same alloy.
2. The sample and experimental procedure The sample was shaped like a flat dumbbell, cut from a 4)< 5 )<0.27 mm 3 polycrystalline Fe49Rhsl alloy wafer, of which the details on heat treatment etc. are described in ref. [4]. The width and length of the narrow part of the sample are 1.841 and 6.538 mm, respectively. Holes, 0.5 mm in diameter, were drilled 234
in the wide parts of the sample. Then the sample was cleaned and annealed in vacuum at 1300 K for 10 h followed by ice water quenching. The thermal expansion measurements were done in vacuum ( ~ 10 - 3 Pa) by use of the strain gauge technique, the gauge being connected to a d c bridge. The temperature was varied from 273 to 373 IL In order to stabilize the AF-F transition parameters, the sample was exposed to 15 heating-cooling cycles in the temperature range mentioned above before the measurements. The electroresistance has been measured under a constant tensile stress up to 529 M N / m 2. A tensile stress was applied on the sample using flexible steel ropes, which were fed through the sample holes. The ends of the ropes were then knotted. In order to rule out the influence of thermal hysteresis of the AF-F transition on the results of the elastocaloric effect measurements the sample was driven to the antiferromagnetic state before each measurement for which purpose it was sufficient to cool it to 273 K. Then the sample was heated to a certain temperature and the elastocaloric effect was measured under a quickly applied tensile stress. This procedure allowed one to provide a replication of the experimental results. The sample temperature was monitored with a copper-constantan thermocouple.
Elsevier Science Publishers B.V.
Volume 171, number 3,4
PHYSICS LETTERSA
3. Results and discussion
The temperature dependence of the thermic expansion of the alloy AI/I is shown in fig. 1. In the temperature range 291-321 K the AI/I value experiences a change by 0.27%. The quickest change of AI/I occurs at 315.6 K. This temperature one considers as the A F - F transition critical temperature Tk. Extrapolation of the shown curve to Tk indicates a relative change of the sample length during the transition [ (Ir--I~)/lAF]T=2.609× 10 -3. Alloy electroresistance p versus temperature relations are shown in fig. 2 for a sample heated in the
f ~2
'O
28o
26o
~o
3io
A F - F transition range under various tensile stresses e. The transition temperatures Tk for various a are determined as the ones where the derivatives dp/dT have a minimum value. In an unstressed state ( a = 0 ) the A F - F transition critical temperature is the same as the one determined from the AI/I(T) plots. The line TkoffiTk+(dTk/da)a, where Tk=315.4 K and ( d T k = / d e ) = - 1.975 X 10 - s K m e / N , calculated using the least-squares method, is a good approximation for the Tk(a) dependence. The data of elastocaloric effect versus temperature are shown in fig. 3. As one would expect, under conditions close to adiabatical ones the applied extension in the A F - F transition range causes an abrupt cooling of the FeRh alloy sample. The temperature jump value AT strongly depends on the initial sample temperature, and increases as a increases. While a increases, the peak of the A T ( T ) plot shifts towards lower temperatures. The maximum values of the effect and the temperatures, at which they have been observed, are listed in table 1. For the first-order A F - F transition, induced by a tensile stress, the Clapeyron-Clausius equation takes the following form,
3~o dTk/da= -
T0¢)
7 December 1992
(AI/ I) ( dAS)-1,
(I)
Fig. 1. Temperature dependence of the linear dilatation in Fed9Rhsl alloy: ( o ) heating, (.) cooling.
"
1
~-10}
290
T(K) 2go 298 506 [ ".,~
2 ' ~
5t_~4
\ \ h ~ l*
500
510
520
Tt'K) Fig. 2. Temperaturedependence of the resistivityof Fe4~Rhstelloy: (o) 0, (A) 56, (D) 151, (v) 238, (<>) 336, (~) 433, (~) 529 MN/m 2.
Fig. 3. Temperature dependence of the elastocaloric effect for Fe4~Rhs~alloy under various tensile s ~ : (A) 56, (D) 151, (v) 238, (<>) 336, ( , ) 433, (4) 529 MN/m 2. 235
Volume 171, number 3,4
PHYSICS LETTERS A
Table 1 Critical temperatures of the AF-F transition (Tk), maximum values of the elastoealoric effect (AT)maxand the initial temperatures (Ti), at which they have been observed under various tensile stresses ¢y. a (10s N/m 2)
Tk (K)
Tl (K)
(AT)m~ (K)
0 56 151 238 336 433 529
315.6 314.3 312.6 310.2 308.5 306.6 305.5
314.83 314.40 313.90 312.15 311.90 311.15
- 1.00 -2.47 -3.15 -4.07 -4.72 -5.17
where d is the alloy density. When the A F - F transition occurs at the critical temperature Tk, the alloy entropy change is AS= - [(lr--lAr)/tAr]
(dAFdTk/da)-l,
(3)
In the AF state, at the temperature Tk the alloy
236
specific heat capacity is CAr = 470 J / k g K [5 ]. Using the calculated value o f the entropy j u m p we obtain (A T) s = - ( 8.7 + 0.5 ) K. The maximal experimental value o f AT accounts for 59% o f the calculated one, which may be attributed to the nonisothermal conditions o f the transition, in the real sample. The abrupt cooling effect o f the FeRh alloy, which takes place at the A F - F transition, adiabatically induced by a tensile stress, m a y be o f practical use, and the anomalously large values o f the temperature j u m p AT, calculated by use o f the thermodynamic formulae (3), is a fact that gives rise to looking for new techniques o f alloy preparation and heat treatment, which would provide A F - F transition parameters close to the ones expected from the model considerations.
(2)
where dAr= 101 1 1 k g / m 3 is the alloy density in the AF state, determined by use o f the R6ntgen spectral fluorescent technique. Using the experimental data quoted above, we obtain the entropy change as ~ S = 13+ 1 J / k g K and the latent heat o f the transition as Q=Tk~S = (41 _+3) × 102 J/kg. In the case of an isothermic transformation induced by an external exposure at the transition temperature under adiabatical conditions, the alloy temperature change is ( A T ) s = - Tk AS/CAr.
7 December 1992
References
[ I ] T.
Tarnoczi,
A
vas-rhodium
antiferrom{tgneses-
ferrmml~a'nesestIt~lakld'tmtn~kvizsslilata, Rep. Cent. Res. Inst. Phys., Hungary, Vol. 12 (1964) pp. 3-16. [2] L. Pal, T. Tarnoczi, P. Szabo, E. Kren andJ. Toth, in: Proe. Int. Conf. on Magnetism, Nottlngham (1964) pp. 158-161. [ 3 ] M.J. Richardson, D. Melville and J.A. Rieodeau, Phys. Lett. A46 (1973) 153. [4 ] S.A.Nikitin, G. Myalikgnlyev,M.P. Annaorazov,A.L. Tyurin, A.M. Tishin and ICA. Asatryan, Phys. Lett. A 148 (1990) 363. [5] M.P. Annaorazov, ICA. Asatryan, G. Myalikgnlyev, S.A. Nikitin, A.N. Tishin and A.L. Tyurin, The alloys of Fc-Rh system as a new class of working material for magnetic refrigerators,Cryogenics (in press).
PHYSICS LETTERS A
Giant elastocaloric effect in FeRh alloy S.A. Nikitin a, G. Myalikgulyev b, M.P. A n n a o r a z o v a, A.L. T y u r i n b, R.W. M y n d y e v b a n d S.A. Akopyan b • Department of Physics, Moscow State University, 119899 Moscow, Russian Federation b Department of Physics, Turkmen State University, 744014 Ashkhabad, Turkmenistan Received 31 August 1992; accepted for publication 10 September 1992 Communicated by V.M. Asranovich
The elastocaloric effect, the electrical resistivity and the thermal expansion have been investigated in a quenched sample of Fe49Rhsl alloy. The giant negative temperature change, resulting from a tensile stress of 529 MN/m 2 applied to the sample, is found to be 5.17 IC Using the Clapeyron-Clausius equation, the entropy jump and the anti.ferromagnetism-ferromagnetism transformation latent heat have been determined, the transformation being induced by the tensile stress applied to this alloy.
1. Introduction The thermal expansion and the thermal stress effects upon the temperature of transformation from the antiferromagnetic state to the ferromagnetic state (AF-F) were investigated in refs. [1,2]. The numerical estimates, obtained by the use of these resuits, and the specific heat data [ 3 ] have established that the temperature of FeRh alloy decreases by 1517 during the AF-F transition, induced by a tensile stress in adiabatic conditions. Furthermore, a giant negative magnetocaloric effect ( 13 K) was found [4 ] in a quenched Fe49Rhs'~ sample under magnetic field induction near 2 T. In order to gain additional information on the thermodynamic features of the AFF transition in the Fe-Rh system, it is of interest to carry out measurements on the elastocaloric effect for samples of the same alloy.
2. The sample and experimental procedure The sample was shaped like a flat dumbbell, cut from a 4)< 5 )<0.27 mm 3 polycrystalline Fe49Rhsl alloy wafer, of which the details on heat treatment etc. are described in ref. [4]. The width and length of the narrow part of the sample are 1.841 and 6.538 mm, respectively. Holes, 0.5 mm in diameter, were drilled 234
in the wide parts of the sample. Then the sample was cleaned and annealed in vacuum at 1300 K for 10 h followed by ice water quenching. The thermal expansion measurements were done in vacuum ( ~ 10 - 3 Pa) by use of the strain gauge technique, the gauge being connected to a d c bridge. The temperature was varied from 273 to 373 IL In order to stabilize the AF-F transition parameters, the sample was exposed to 15 heating-cooling cycles in the temperature range mentioned above before the measurements. The electroresistance has been measured under a constant tensile stress up to 529 M N / m 2. A tensile stress was applied on the sample using flexible steel ropes, which were fed through the sample holes. The ends of the ropes were then knotted. In order to rule out the influence of thermal hysteresis of the AF-F transition on the results of the elastocaloric effect measurements the sample was driven to the antiferromagnetic state before each measurement for which purpose it was sufficient to cool it to 273 K. Then the sample was heated to a certain temperature and the elastocaloric effect was measured under a quickly applied tensile stress. This procedure allowed one to provide a replication of the experimental results. The sample temperature was monitored with a copper-constantan thermocouple.
Elsevier Science Publishers B.V.
Volume 171, number 3,4
PHYSICS LETTERSA
3. Results and discussion
The temperature dependence of the thermic expansion of the alloy AI/I is shown in fig. 1. In the temperature range 291-321 K the AI/I value experiences a change by 0.27%. The quickest change of AI/I occurs at 315.6 K. This temperature one considers as the A F - F transition critical temperature Tk. Extrapolation of the shown curve to Tk indicates a relative change of the sample length during the transition [ (Ir--I~)/lAF]T=2.609× 10 -3. Alloy electroresistance p versus temperature relations are shown in fig. 2 for a sample heated in the
f ~2
'O
28o
26o
~o
3io
A F - F transition range under various tensile stresses e. The transition temperatures Tk for various a are determined as the ones where the derivatives dp/dT have a minimum value. In an unstressed state ( a = 0 ) the A F - F transition critical temperature is the same as the one determined from the AI/I(T) plots. The line TkoffiTk+(dTk/da)a, where Tk=315.4 K and ( d T k = / d e ) = - 1.975 X 10 - s K m e / N , calculated using the least-squares method, is a good approximation for the Tk(a) dependence. The data of elastocaloric effect versus temperature are shown in fig. 3. As one would expect, under conditions close to adiabatical ones the applied extension in the A F - F transition range causes an abrupt cooling of the FeRh alloy sample. The temperature jump value AT strongly depends on the initial sample temperature, and increases as a increases. While a increases, the peak of the A T ( T ) plot shifts towards lower temperatures. The maximum values of the effect and the temperatures, at which they have been observed, are listed in table 1. For the first-order A F - F transition, induced by a tensile stress, the Clapeyron-Clausius equation takes the following form,
3~o dTk/da= -
T0¢)
7 December 1992
(AI/ I) ( dAS)-1,
(I)
Fig. 1. Temperature dependence of the linear dilatation in Fed9Rhsl alloy: ( o ) heating, (.) cooling.
"
1
~-10}
290
T(K) 2go 298 506 [ ".,~
2 ' ~
5t_~4
\ \ h ~ l*
500
510
520
Tt'K) Fig. 2. Temperaturedependence of the resistivityof Fe4~Rhstelloy: (o) 0, (A) 56, (D) 151, (v) 238, (<>) 336, (~) 433, (~) 529 MN/m 2.
Fig. 3. Temperature dependence of the elastocaloric effect for Fe4~Rhs~alloy under various tensile s ~ : (A) 56, (D) 151, (v) 238, (<>) 336, ( , ) 433, (4) 529 MN/m 2. 235
Volume 171, number 3,4
PHYSICS LETTERS A
Table 1 Critical temperatures of the AF-F transition (Tk), maximum values of the elastoealoric effect (AT)maxand the initial temperatures (Ti), at which they have been observed under various tensile stresses ¢y. a (10s N/m 2)
Tk (K)
Tl (K)
(AT)m~ (K)
0 56 151 238 336 433 529
315.6 314.3 312.6 310.2 308.5 306.6 305.5
314.83 314.40 313.90 312.15 311.90 311.15
- 1.00 -2.47 -3.15 -4.07 -4.72 -5.17
where d is the alloy density. When the A F - F transition occurs at the critical temperature Tk, the alloy entropy change is AS= - [(lr--lAr)/tAr]
(dAFdTk/da)-l,
(3)
In the AF state, at the temperature Tk the alloy
236
specific heat capacity is CAr = 470 J / k g K [5 ]. Using the calculated value o f the entropy j u m p we obtain (A T) s = - ( 8.7 + 0.5 ) K. The maximal experimental value o f AT accounts for 59% o f the calculated one, which may be attributed to the nonisothermal conditions o f the transition, in the real sample. The abrupt cooling effect o f the FeRh alloy, which takes place at the A F - F transition, adiabatically induced by a tensile stress, m a y be o f practical use, and the anomalously large values o f the temperature j u m p AT, calculated by use o f the thermodynamic formulae (3), is a fact that gives rise to looking for new techniques o f alloy preparation and heat treatment, which would provide A F - F transition parameters close to the ones expected from the model considerations.
(2)
where dAr= 101 1 1 k g / m 3 is the alloy density in the AF state, determined by use o f the R6ntgen spectral fluorescent technique. Using the experimental data quoted above, we obtain the entropy change as ~ S = 13+ 1 J / k g K and the latent heat o f the transition as Q=Tk~S = (41 _+3) × 102 J/kg. In the case of an isothermic transformation induced by an external exposure at the transition temperature under adiabatical conditions, the alloy temperature change is ( A T ) s = - Tk AS/CAr.
7 December 1992
References
[ I ] T.
Tarnoczi,
A
vas-rhodium
antiferrom{tgneses-
ferrmml~a'nesestIt~lakld'tmtn~kvizsslilata, Rep. Cent. Res. Inst. Phys., Hungary, Vol. 12 (1964) pp. 3-16. [2] L. Pal, T. Tarnoczi, P. Szabo, E. Kren andJ. Toth, in: Proe. Int. Conf. on Magnetism, Nottlngham (1964) pp. 158-161. [ 3 ] M.J. Richardson, D. Melville and J.A. Rieodeau, Phys. Lett. A46 (1973) 153. [4 ] S.A.Nikitin, G. Myalikgnlyev,M.P. Annaorazov,A.L. Tyurin, A.M. Tishin and ICA. Asatryan, Phys. Lett. A 148 (1990) 363. [5] M.P. Annaorazov, ICA. Asatryan, G. Myalikgnlyev, S.A. Nikitin, A.N. Tishin and A.L. Tyurin, The alloys of Fc-Rh system as a new class of working material for magnetic refrigerators,Cryogenics (in press).