Influence of Co addition on the magnetocaloric effect of FeCoSiAlGaPCB amorphous alloys

Abstract

The FeCoSiAlGaPCB alloys can be prepared as bulk amorphous materials, with outstanding mechanical properties and increased electrical resistivity. These features can be beneficial for their application as a magnetic refrigerant. The influence of Co addition on the magnetic entropy change of the alloy has been studied. This compositional modification displaces the temperature of the peak entropy change closer to room temperature, but reduces the refrigerant capacity of the material. For the Co-free alloy, the peak entropy change is increased with respect to a Finemet alloy containing Mo, but its refrigerant capacity is not enhanced. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2188385͔Magnetic refrigeration is a field of research that has gained increasing attention, as it is considered an alternative to the gas compression-expansion cycle. At temperatures close to room temperature, rare-earth-based materials are among the most relevant ones. [1][2][3][4] To display a big magnetocaloric response, two requirements have to be fulfilled: the material needs to exhibit a big magnetic moment and, also, a strong temperature dependence of magnetization close to the working temperature. This second condition, related to a magnetic phase transition, can be achieved in two different ways. Either by a first-order phase transition, which produces an abrupt temperature change of the magnetic moment and, therefore, a remarkable peak in the magnetic entropy change ͑⌬S M ͒ at the transition temperature, or by a second order phase transition, which causes a more smeared peak in ⌬S M . However, the remarkable hysteresis that appears in some materials, associated to first order phase transitions, may reduce the actual efficiency of the cooling process. 5 It has been pointed out, nevertheless, that in order to compare the characteristics of different materials as candidates for magnetic refrigerants, their refrigerant capacity ͑RC͒ in a reversible cycle, connected to the entropy absorbed by the refrigerant at the cold end of the cycle and its temperature span, should be used. 6 The search for low-cost materials for high-temperature magnetic refrigeration is a field of current interest. 7-12 Recently it has been shown that some soft-magnetic amorphous alloys are good candidates for this application, 11 with a refrigerant capacity that is comparable to that of low-hysteretic Gd-based materials. 4 It has also been shown that the nanocrystallization of the alloy, although broadening the ⌬S M

A constant magnetocaloric response in FeMoCuB amorphous alloys with different Fe∕B ratios

“…5 shows the thermal dependence of n for the different studied alloys. In agreement with previous experimental data, [15][16][17][18][19] the general behavior consists in ͑a͒ a value of n close to 1 for temperatures well below the transition temperature ͑b͒ a smooth decrease of n down to values close to 0.75 at T pk , and ͑c͒ a subsequent increase to n =2 in the paramagnetic region. These values have been ascribed 23 to ͑a͒ the temperature independent magnetization for moderate magnetic fields at low temperatures, ͑b͒ a relationship between n and the two critical exponents controlling the field dependence of magnetization at the Curie temperature ͑␦͒ and the thermal dependence of magnetization ͑␤͒, of the form n =1+͑1/␦͒͑1−1/␤͒, and ͑c͒ a consequence of the linear field dependence of magnetization where the Curie-Weiss law is valid, respectively.…”

“…For example, the addition of Co in alloys with high metalloid content produces a decrease of the Curie temperature of the material, making it closer to room temperature, but at the expense of a reduction in both its ͉⌬S M pk ͉ and its refrigerant capacity ͑RC͒. 18 A similar effect has been observed for Cr and/or Mo substitution in bulk amorphous alloys. 19 Therefore, the application of hightemperature magnetic refrigerants would require the search for alloying elements which would optimize the Curie temperature of the material without a detrimental effect on the MCE response.…”

“…[9][10][11][12][13][14][15][16] Albeit the maximum magnetic entropy change, ͉⌬S M pk ͉, for these alloys is modest when compared to that of rare-earth-based materials, the remarkable difference in material costs is an incentive for studying their suitability as magnetic refrigerants. Besides their reduced magnetic hysteresis ͑virtually negligible͒, the high electrical resistivity ͑which would decrease eddy current losses͒, tunable Curie temperature, and, in the case of bulk amorphous alloys, [17][18][19][20] outstanding mechanical properties are beneficial characteristics for a successful application of the material.…”

Enhanced magnetocaloric response in Cr∕Mo containing Nanoperm-type amorphous alloys

“…In particular, there is a growing interest in studying the applicability of soft magnetic amorphous alloys as magnetic refrigerants [9][10][11][12][13][14][15][16][17][18][19][20] due to their reduced magnetic hysteresis ͑vir-tually negligible͒, higher electrical resistivity ͑which would decrease eddy current losses͒, and tunable Curie temperature T Curie . Among the different compositional series of soft magnetic amorphous alloys, Nanoperm-type alloys are those that currently exhibit the highest RC values, having also among the highest values of ͉⌬S M pk ͉.…”

Magnetocaloric effect in Mn-containing Hitperm-type alloys

“…8 More recently, soft magnetic amorphous alloys are getting increasing attention as low-cost candidates for magnetic refrigeration. [9][10][11][12][13][14][15][16][17][18] ͑According to a well-known bibliographic database, more than 36% of the literature on the magnetocaloric effect in amorphous materials were published since 2005. Considering only the magnetocaloric effect in transition-metal-based amorphous alloys, more than 50% of the papers studying these materials were published since then.͒ Although the maximum magnetic entropy change, ͉⌬S M pk ͉, for these alloys is modest when compared to that of rare-earth-based materials, 1,6 the remarkable difference in material costs is an incentive for studying their suitability as magnetic refrigerants.…”