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Pressure enhancement of the giant magnetocaloric effect in LaFe11.6Si1.4

November 2006
Applied Physics Letters 89(17):172513 - 172513-3

November 2006
89(17):172513 - 172513-3

DOI:10.1063/1.2372584

Source
IEEE Xplore

Authors:

Young Sun

Chinese Academy of Sciences

Zdenek Arnold

Institute of Physics ASCR

Show all 6 authorsHide

The authors have studied the effects of pressure on the magnetocaloric effect in a polycrystalline La Fe 11.6 Si 1.4 sample. The Curie temperature TC of the sample rapidly decreases from 191 K at ambient pressure to 80 K under 8.3 kbar pressure. The metamagnetic transition induced by field at temperatures above TC becomes extremely sharp under high pressure and the critical field Hc of the transition increases fast with increasing temperature. As a result, the giant magnetocaloric effect in La Fe 11.6 Si 1.4 is greatly enhanced by pressure, especially at low magnetic fields. For a field variation of 1 T only, the maximum value of the entropy change is as high as 34 J / kg K .

Low-field H = 100 Oe M-T curves of LaFe 11.6 Si 1.4 under several pressures.

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Color online Entropy change for magnetic field changes of 1 and 5 T under several pressures in LaFe 11.6 Si 1.4 .

…

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Pressure enhancement of the giant magnetocaloric effect in LaFe11.6Si1.4

Young Suna兲

State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080,

China and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese

Academy of Sciences, Beijing 100080, China

Z. Arnold and J. Kamarad

Institute of Physics AS CR, Na Slovance 2, 182 21 Prague 8, Czech Republic

Guang-Jun Wang, Bao-Gen Shen, and Zhao-Hua Cheng

State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences,

Beijing 100080, China

共Received 26 June 2006; accepted 13 September 2006; published online 27 October 2006兲

The authors have studied the effects of pressure on the magnetocaloric effect in a polycrystalline

LaFe11.6Si1.4 sample. The Curie temperature TCof the sample rapidly decreases from 191 K at

ambient pressure to 80 K under 8.3 kbar pressure. The metamagnetic transition induced by ﬁeld at

temperatures above TCbecomes extremely sharp under high pressure and the critical ﬁeld Hcof the

transition increases fast with increasing temperature. As a result, the giant magnetocaloric effect in

LaFe11.6Si1.4 is greatly enhanced by pressure, especially at low magnetic ﬁelds. For a ﬁeld variation

Institute of Physics.关DOI: 10.1063/1.2372584兴

Magnetic refrigeration based on the magnetocaloric ef-

fect 共MCE兲has become a promising competitive technology

for the conventional gas-compression/expansion technique.1

MCE is an intrinsic thermodynamic property of magnetic

materials that results from the coupling of a magnetic system

with a magnetic ﬁeld. It manifests itself as an adiabatic tem-

perature change or an isothermal entropy change in response

to a variation of external magnetic ﬁelds. A variety of mate-

rials has been found to exhibit a large MCE at different tem-

perature ranges. Some of the good examples include Gd

element,2Gd5共SixGe1−x兲4,3Ni–Mn–Ga alloys,4MnAs,5

MnFeP1−xAsx,6LaFe13−xSix,7,8the perovskite manganites,9,10

and others.

Recently, it was found that the MCE in magnetic com-

pounds with strong spin-lattice coupling can be signiﬁcantly

affected by external pressure.11–13 Morellon et al. ﬁrst stud-

ied the effects of pressure on MCE in Tb5Si2Ge2.11 They

found that external pressure can tune the magnetic phase

transition and induce a giant MCE in this material. Mean-

while, Gama et al. recently reported the pressure-induced

colossal MCE in MnAs.12 The maximum value of ⌬Sin

MnAs under a pressure of 0.23 GPa reaches 267 J/ 共kg K兲,

far greater than the assumed magnetic entropy limit. More

recently, our group studied the effects of pressure on the

MCE in a La0.69Ca0.31MnO3manganite and found that the

MCE can be effectively tuned by external pressure.13 All

these studies have demonstrated successfully that the pres-

sure tuning of MCE in certain materials can open an impor-

tant and effective strategy for the development of magnetic

refrigeration based on MCE.

The LaFe13−xSixcompounds and their variants are

among the most promising candidates for magnetic

refrigeration.7,8Recent work has well conﬁrmed that these

compounds exhibit a large magnetovolume effect accompa-

nying with the ﬁrst-order paramagnetic to ferromagnetic

transition.14 Therefore, it is worthwhile to expect a signiﬁ-

cant inﬂuence of external pressure on this phase transition in

LaFe13−xSixand recently, this has been also proven by pres-

sure experiments.15 Nevertheless, the effects of pressure on

the MCE in LaFe13−xSixhave not been reported so far. In this

work, we have performed such a study in a LaFe11.6Si1.4

sample. It is found that the giant MCE in LaFe11.6Si1.4 is

greatly enhanced by pressure. The magnetic entropy change

for a 1 T ﬁeld variation exceeds 30 J/ kg K when under pres-

sures, which sets a record of low-ﬁeld MCE.

Polycrystalline LaFe11.6Si1.4 samples were prepared by

arc melting in an atmosphere of ultrapure argon gas. The

purity of the starting elements was better than 99.9 wt %.

The ingots were remelted three times to ensure homogeneity,

annealed in vacuum at 1273 K for 50 days, and then

quenched in liquid nitrogen. The single phase with the

NaZn13-type structure of as-prepared samples was conﬁrmed

by powder x-ray diffraction at room temperature. The mag-

netization measurements under high hydrostatic pressures

were performed using a superconducting quantum interfer-

ence device magnetometer 共Quantum Design Co.兲in mag-

netic ﬁelds up to 5 T. The sample was compressed in a min-

iature nonmagnetic CuBe pressure cell that was ﬁlled by a

mixture of mineral oils in a role of a liquid pressure-

transmitting medium. Pressure inside the cell was deter-

mined using the Pb pressure sensor. A decrease of pressure in

the clamped CuBe cell with decreasing temperature was

taken into account.16

Figure 1shows the temperature dependence of magneti-

zation of LaFe11.6Si1.4 under several hydrostatic pressures. In

zero pressure, the Curie temperaure TC, determined by the

inﬂection point in the low-ﬁeld 共H=100 Oe兲M-Tcurve with

warming process, is 191 K, consistent with previous reports.

With increasing pressure, TCdecreases dramatically, from

191 K in zero pressure to 80 K in 8.3 kbar pressure. These

results verify the signiﬁcant inﬂuence of pressure on the

phase transition in LaFe11.6Si1.4.

a兲Electronic mail: youngsun@aphy.iphy.ac.cn

APPLIED PHYSICS LETTERS 89, 172513 共2006兲

Downloaded 27 Oct 2006 to 159.226.36.156. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

We then studied the inﬂuence of pressure on the MCE in

LaFe11.6Si1.4. It is well known that the MCE can be evaluated

from the isothermal magnetization curves using a Maxwell

relation.1In order to calculate the entropy change, we mea-

sured the isothermal magnetization curves at a temperature

interval of 2.5 K in the vicinity of TCand an interval of 5 K

away from TC. Figures 2共a兲–2共c兲show the typical isothermal

magnetization curves of LaFe11.6Si1.4 under different pres-

sures. In zero pressure, a metamagnetic transition occurs at a

critical ﬁeld in the paramagnetic state. The metamagnetic

transition decays with increasing temperature and the hyster-

esis eventually disappears at a temperature T0. These results

in zero pressure are similar to previous reports on

LaFe13−xSixcompounds.15 For a 4.5 kbar pressure in which

TCis reduced to 150 K, the magnetization curves become

peculiar above TC. As the ﬁeld increases, the magnetization

increases slowly as expected for a paramagnetic state. Then,

a sudden jump of magnetization, evidencing a very sharp

metamagnetic transition, happens at a critical ﬁeld Hc. The

amplitude of the magnetization jump, more than 100 emu / g,

is strikingly huge. With further increasing ﬁeld, the magne-

tization saturates smoothly. When the ﬁeld returns, the tran-

sition from the high magnetization to the low magnetization

is less sharp and occurs at a much lower ﬁeld, which causes

a huge hysteresis. With increasing temperature, the critical

ﬁeld increases rapidly. At 170 K, the magnetization remains

a low value until the maximum ﬁeld 共5T兲, but it is expected

that the metamagnetic transition would happen at a higher

critical ﬁeld. When the pressure is increased to 8.3 kbars in

which TCis reduced to 80 K, the magnetization of

LaFe11.6Si1.4 becomes more peculiar. Apparent curvature and

hysteresis in magnetization appear even below TC. At and

above TC, the magnetization exhibits very sharp jumps with

huge hysteresis. More interestingly, the magnetization under

8.3 kbars exhibits two separate transitions, one at a lower

critical ﬁeld with a small magnetization jump and another at

a higher critical ﬁeld with a big jump.

From Fig. 2, it is apparent that the metamagnetic transi-

tion is very sensitive to temperature. It appears immediately

at TCand the critical ﬁeld shifts rapidly as temperature in-

creases. Because of the sharpness and the temperature sensi-

tivity of these metamagnetic transitions under pressure, a gi-

ant MCE would be expected, especially near TC. Figure 3

shows the calculated entropy change ⌬Susing the isothermal

magnetization curves. In zero pressure, the maximum values

of ⌬Sare about 12 and 24 J / 共kg K兲for 1 and 5 T ﬁeld

variations, respectively. Under a 4.5 kbar pressure, ⌬Sshows

a giant peak at TC共150 K兲. For a small ﬁeld variation of 1 T

only, the peak value of ⌬Sis as high as 34 J / 共kg K兲. This

value is strikingly high given the fact that the maximum of

⌬Sfor a 1 T ﬁeld variation in typical materials showing a

giant MCE is less than 15 J/共kg K兲. However, the ⌬Sfor a

1 T ﬁeld variation drops quickly to a low value when tem-

perature increases. This is due to the fact that 1 T ﬁeld is not

FIG. 1. Low-ﬁeld 共H= 100 Oe兲M-Tcurves of LaFe11.6Si1.4 under several

pressures.

FIG. 2. 共Color online兲Isothermal M-Hcurves of LaFe11.6Si1.4 around TC

under different pressures: 共a兲zero pressure, 共b兲4.5 kbars, and 共c兲8.3 kbars.

FIG. 3. 共Color online兲Entropy change for magnetic ﬁeld changes of 1 and

5 T under several pressures in LaFe11.6Si1.4.

172513-2 Sun et al. Appl. Phys. Lett. 89, 172513 共2006兲

Downloaded 27 Oct 2006 to 159.226.36.156. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

enough to cause a metamagnetic transition above TCso that

the magnetization remains a low value and the entropy

changes little as the ﬁeld varies. For a 5 T ﬁeld variation, the

peak value of ⌬Sreaches 38 J / 共kg K兲, a little higher than

that for a 1 T variation. Nevertheless, the shape of ⌬Sis

peculiar. After the peak at TC, a plateau of ⌬Sremains for a

broad temperature range above TC. When temperature is

higher than 167 K, ⌬Sdrops to a low value because 5 T ﬁeld

is not enough to cause a metamagnetic transition above this

temperature. It is expected that the plateau of ⌬Swould last

to higher temperatures when a higher ﬁeld variation 共H

⬎5T兲is applied. Under 8.3 kbar pressure, the shape of ⌬S

is similar to that in 4.5 kbars but the maximum value is more

giant, reaching 60 J/共kg K兲for a 5 T ﬁeld variation.

These results for the ﬁrst time demonstrate that the iso-

thermal entropy change in LaFe11.6Si1.4 can be greatly en-

hanced by pressure. Pressure enhancement of the entropy

change has recently been observed in MnAS and

Tb5Si2Ge2.11,12 It has been proposed that the enhancement of

MCE by pressure is due to the contribution from the lattice

entropy when there is strong magnetostructural coupling as-

sociated with the ﬁrst-order magnetic phase transition. This

argument seems also true for LaFe11.6Si1.4 since a strong

magnetovolume effect accompanying with the ﬁrst-order

metamagnetic transition in LaFe1−xSixhas been well

recognized.14 The signiﬁcant enhancement of the low-ﬁeld

MCE as well as the plateau shape of the high-ﬁeld MCE may

have important impact on practical applications.

This work was supported by the State Key Project of

Fundamental Research and the National Natural Science

Foundation of China. The ﬁnancial support from the Project

No. 202/06/0178 of the Grant Agency of the Czech Republic

is also acknowledged.

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Article

Jun 1997

An extremely large magnetic entropy change has been discovered in Gd{sub 5}(Si{sub 2}Ge{sub 2}) when subjected to a change in the magnetic field. It exceeds the {ital reversible} (with respect to an alternating magnetic field) magnetocaloric effect in any known magnetic material by at least a factor of 2, and it is due to a first order [ferromagnetic (I){leftrightarrow}ferromagnetic (II)] phase transition at 276K and its unique magnetic field dependence. {copyright} {ital 1997} {ital The American Physical Society}

Giant magnetocaloric effect of MnAs1−xSbx

Article

Nov 2001
APPL PHYS LETT

A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained. © 2001 American Institute of Physics.

Large magnetic entropy change in the colossal magnetoresistance material La2/3Ca1/3MnO3

Article

Sep 2000
J MAGN MAGN MATER

In this paper, we present a study of magnetocaloric effect in the colossal magnetoresistance material La2/3Ca1/3MnO3. From the measurements of temperature dependence of magnetization under various magnetic fields, we have discovered a large magnetic entropy change associated with the ferromagnetic–paramagnetic transition. This result suggests that perovskite manganites are suitable candidates as working substances in magnetic refrigeration technology.

High pressure cells for magnetic measurements—Destruction and functional tests

Article

Dec 2004

The design of nonmagnetic CuBe and multilayer ( Cu Be + MP 35 N ) hydrostatic pressure cells for magnetization and magnetostriction measurements in a pressure range up to 2 GPa at temperatures down to 5 K and in fields up to 14 T is presented. The safety operation of the cells is based on destruction tests described in this work. An influence of the pressure cells on measured magnetic magnitudes and the temperature induced pressure changes in the clamped cells have been carefully studied in a temperature range from 350 K down to 5 K using different pressure transmitting media.

Magnetic entropy change in Ni51.5Mn22.7Ga25.8 alloy

Article

Jul 2000
APPL PHYS LETT

A considerable magnetic entropy change has been observed in Ni 51.5 Mn 22.7 Ga 25.8 alloys under a field of 0.9 T. This change originates from a sharp magnetization jump which is associated with a martensitic to austenitic structure transition. The large low field entropy change and the adjustable martensic–austensic transition temperature indicate a great potential of Ni–Mn–Ga as working materials for magnetic refrigerants in a wide temperature range. © 2000 American Institute of Physics.

Large magnetocaloric effect in La(FexSi1-x)13 itinerant-electron metamagnetic compounds

Article

Sep 2002
APPL PHYS LETT

The magnetocaloric effect (MCE) originated from the itinerant-electron metamagnetic transition for La ( Fe x Si 1-x)13 compounds has been investigated. With increasing Fe concentration, the MCE is enhanced and both the isothermal magnetic entropy change ΔSm and the adiabatic temperature change ΔT ad for the compound with x=0.90 are -28 J/kg K and 8.1 K, respectively, by changing the magnetic field from 0 to 2 T. Similar large MCE values are achieved around room temperature by controlling the Curie temperature by means of hydrogen absorption. Consequently, La ( Fe x Si 1-x)13 compounds are promising as magnetic refrigerant materials working in relatively low magnetic fields. © 2002 American Institute of Physics.