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  • 1
    Electronic Resource
    Electronic Resource
    Heat capacity near first order phase transitions and the magnetocaloric effect: An analysis of the errors, and a case study of Gd5(Si2Ge2) and Dy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6315-6321 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The heat capacity measured in an adiabatic heat pulse calorimeter with nonzero heat capacity suffers from intrinsic errors in the vicinity of a first order phase transition. When these errors are carried over into the calculation of the magnetocaloric effect, the latter also suffers from large systematic errors. The sources of the intrinsic errors in the heat capacity near the first order phase transition temperature and the procedures to minimize them are discussed. The experimental heat capacity data of Gd5(Si2Ge2) and ultra pure Dy, both of which exhibit first order phase transition, are used to confirm the theoretical conclusions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371734
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic refrigeration materials (invited) (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5365-5368 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Research on the magnetocaloric effect and its application for cooling near room temperature over the past few years has helped to move this phenomenon from a scientific curiosity to an emerging technology. Two of the most important advances include the demonstration which proved that it is possible to obtain significant cooling powers (600 W) at high Carnot efficiencies (60%) and with a large coefficient of performance (15) near room temperature in moderately strong magnetic fields (≤5 T); and the discovery of the giant magnetocaloric effect in the Gd5(SixGe1−x)4 series of alloys. Also, new knowledge about the magnetocaloric effect has been gained. This includes: the relationship between the nature of the magnetic transformation(s) and the temperature dependence of the magnetocaloric effect, the entropy utilized in the magnetocaloric process, and the role of impurities on the giant magnetocaloric effect.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369979
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetocaloric effect from indirect measurements: Magnetization and heat capacity (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 565-575 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Accurate values for the magnetocaloric effect can be obtained from both magnetization and heat-capacity data. A reliable estimate of the experimental errors in the calculated magnetocaloric effect can be made from the known experimental errors of the measured physical properties. Attempts in the past to simplify the basic thermodynamic relation to allow the calculation of the adiabatic temperature change from the heat capacity at constant field and the magnetic entropy change calculated from the magnetization data fail because the assumption that heat capacity is magnetic-field independent is erroneous. A suitable approach to carry out these calculations from the combined heat capacity and magnetization data is suggested. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370767
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  • 4
    Electronic Resource
    Electronic Resource
    A 3–350 K fast automatic small sample calorimeter (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 4196-4207 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A description of a fully automated calorimeter for rapid measuring the heat capacity of solids in the temperature region from ∼3 to ∼350 K and in magnetic fields from 0 to 10 T is given. A comprehensive mathematical analysis of the semiadiabatic heat pulse technique for heat capacity measurements on solid materials resulted in the development of the necessary formal algorithms for the complete automatization of the data collection process. Simultaneously a procedure for the on-line evaluation of uncertainties in the measured heat capacity data is developed. An approach which eliminates the need for a separate temperature sensor(s) attached to an adiabatic heat shield(s) used to maintain semiadiabatic conditions during heat pulse heat capacity measurements has been proposed and tested. The sensorless technique provides reliable control of the heat transfer inside a vacuum chamber and results in accurate heat capacity data. The calibration results show that the heat capacity can be measured with an average accuracy better than 1% on small samples (∼1 g) over the whole temperature region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148367
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  • 5
    Electronic Resource
    Electronic Resource
    The correlation of the magnetic properties and the magnetocaloric effect in (Gd1−xErx)NiAl alloys (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5677-5685 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of the magnetic properties of several (Gd1−xErx)NiAl alloys (where x=0, 0.30, 0.40, 0.46, 0.50, 0.55, 0.60, 0.80, and 1.00) was undertaken using both ac and dc magnetic and heat capacity measurements in an attempt to understand the table-like magnetocaloric effect previously observed in (Gd0.54Er0.46)NiAl. Results indicate the presence of both antiferromagnetic and ferromagnetic ordering processes in all alloys containing Gd. For ErNiAl, a metamagnetic transition from an antiferromagnetic ground state was observed. Within each alloy, several magnetic transitions occur over a temperature range from 10 K [in (Gd0.20Er0.80)NiAl] up to 35 K (in GdNiAl), with all but the lowest temperature transition shifting to higher temperatures with increasing Gd content. The change in magnetic entropy (ΔSmag) induced by a change in field is observed to peak around the Néel temperature for ErNiAl while gradually broadening and shifting toward the Curie temperature as the Gd content is increased. For Gd-rich alloys, a significant contribution to ΔSmag is observed at both the low and high temperature transitions, resulting in a rounded, skewed caret-like temperature profile of the magnetocaloric effect. Factors, which are believed to contribute to this effect, include the presence and temperature spacing of multiple zero-field transitions, which most likely result from competing anisotropy and exchange interactions within a frustrated hexagonal spin lattice. This leads to broad peaks in the magnetic heat capacity that span several transition temperatures, providing for a substantial ΔSmag over an extended temperature range. This characteristic is desired for application to magnetic refrigeration, where certain thermodynamic cycles (e.g., Ericsson cycle) require specific temperature profiles of the magnetocaloric effect in refrigerant materials (e.g., a constant change in magnetic entropy as a function of temperature within the region of cooling). In general, the best materials are those which supply the maximum amount of cooling over the widest temperature range. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368830
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  • 6
    Electronic Resource
    Electronic Resource
    Some common misconceptions concerning magnetic refrigerant materials (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4614-4622 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relationships between both extensive and intensive properties quantifying the magnetocaloric effect, i.e., between the isothermal entropy change and the adiabatic temperature change, respectively, have been analyzed. An extensive measure of the magnetocaloric effect alone, without considering another important and also extensive thermodynamic property, i.e., the heat capacity, may lead to biased conclusions about the size of the magnetocaloric effect and, consequently, about the applicability of a magnetic material as a magnetic refrigerant. The near room temperature magnetocaloric properties of the colossal magnetoresistive manganites [(R1−xMx)MnO3, where R=lanthanide metal and M is alkaline earth metal] and the recently discovered Fe-based intermetallic material (LaFe11.47Co0.23Al1.3) have been reaccessed and correctly compared with those of the metallic Gd prototype. Our analysis has shown that these 3d materials are inferior to Gd by a factor of 2 or more because of the high values of the heat capacity per unit mass. Also a comparison of the volumetric isothermal entropy change, which is a critical parameter for the operation of a refrigeration unit, indicates that Gd is superior to these 3d materials for practical applications. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1405836
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  • 7
    Electronic Resource
    Electronic Resource
    New type of magnetocaloric effect: Implications on low-temperature magnetic refrigeration using an Ericsson cycle (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2739-2741 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-temperature, high magnetic field heat capacity (1.5 to 70 K and 0 to 9.85 T), dc and ac magnetic behaviors of the compound (Gd0.54Er0.46)AlNi show that field-induced magnetic entropy change is significant and almost constant over the temperature region of ∼15 to ∼45 K. The resulting temperature dependence of the magnetocaloric effect, nearly constant over a 30+ K temperature range, is unprecedented (most magnetic materials have a caretlike shape temperature dependence). These data show that (Gd0.54Er0.46)AlNi can be used as an effective active magnetic regenerator material for an Ericsson-cycle magnetic refrigerator, and could substitute for complex composite layered materials suggested earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111459
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  • 8
    Electronic Resource
    Electronic Resource
    (Dy0.5Er0.5)Al2: A large magnetocaloric effect material for low-temperature magnetic refrigeration (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 253-255 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-temprature heat capacity and ac and dc magnetic properties of (Dy0.5Er0.5)Al2 have been studied as a function of magnetic fields up to ∼10 T. The magnetocaloric effect in (Dy0.5Er0.5)Al2 is 30% larger than that of the prototype material, GdPd. Magnetic measurements show that there is no measurable magnetic hysteresis above ∼17 K. These results suggest that (Dy0.5Er0.5)Al2 would be a significantly better magnetic refrigerant than GdPd.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111520
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  • 9
    Electronic Resource
    Electronic Resource
    Tunable magnetic regenerator alloys with a giant magnetocaloric effect for magnetic refrigeration from ∼20 to ∼290 K (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3299-3301 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x≤0.5. For the temperature range between ∼50 and ∼280 K it exceeds the reversible (with respect to alternating magnetic field) ΔSmag for any known magnetic refrigerant material at the corresponding Curie temperature by a factor of 2–10. The two most striking features of this alloy system are: (1) the first order phase transformation, which brings about the large ΔSmag in Gd5(SixGe1−x)4, is reversible with respect to alternating magnetic field, i.e., the giant magnetocaloric effect can be utilized in an active magnetic regenerator magnetic refrigerator; and (2) the ordering temperature is tunable from ∼30 to ∼276 K by adjusting the Si:Ge ratio without losing the giant magnetic entropy change. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119206
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  • 10
    Electronic Resource
    Electronic Resource
    MAGNETOCALORIC MATERIALS (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 30 (2000), S. 387-429 
    Details
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In the last decade of the twentieth century there has been a significant increase in research on a more than 100-year old phenomenon-the magnetocaloric effect (MCE). As a result, many new materials with large MCEs (and many with lesser values) have been discovered, and a much better understanding of this magneto-thermal property has resulted. In this review we briefly discuss the principles of magnetic cooling (and heating); the measurement of the magnetocaloric properties by direct and indirect techniques; the special problems that can arise; and the MCE properties of the 4f lanthanide metals, their intra-lanthanide alloys and their compounds [including the giant MCE Gd5(SixGe1-x)4 phases]; the 3d transition metals, their alloys and compounds; and mixed lanthanide-3d transition metal materials (including the La manganites).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.matsci.30.1.387
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