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Polycrystalline ErCo4Ge2 was investigated by magnetic susceptibility and heat capacity measurements. The results show that ErCo4Ge2 undergoes a transition from the paramagnetic to the antiferromagnetic (AFM) state around 2.6 K. The second order character of this magnetic transition is confirmed from the lambda-like peak of the heat capacity data. Both χ' and χ" of ErCo4Ge2 are strongly dependent on the ac magnetic field frequency and bias dc magnetic field. A field induced metamagnetic transition from AFM to ferromagnetic state is observed below TN. Under a magnetic field change of 50 kOe, the maximum value of the magnetic entropy change (magnetocaloric effect) - ΔSM is 14.2 J/kg K at 2.75 K and the adiabatic temperature change ΔTad is 5.7 K. In particular, a large - ΔSM value of 11.7 J/kg K is achieved for a low magnetic field change of 20kOe. [ABSTRACT FROM AUTHOR]

We report on the effect of Er addition to PrAl2 on the lattice parameters, magnetic behavior, heat capacity, and magnetocaloric effect by using x-ray diffraction, magnetization, and heat capacity measurements. Unlike Pr0.6Er0.4Al2, other alloys we studied in the pseudobinary (Pr1-xErx)Al2 system do not exhibit a sharp peak in heat capacity with the application of magnetic field. Both the cubic lattice parameter and the Curie temperature decrease with increasing Er concentration. The nuclear specific heat coefficient decreases from 660 mJ K mol-1 for x=0.05 to a nearly negligible value for x=0.95. The magnetic entropy and adiabatic temperature change varies from 2 to 4 J mol-1 K-1 and 2.5 to 5K at ΔH=20 kOe for x=0.05 to 0.95, respectively. These values of the magnetocaloric effect are comparable to those of the other rare-earth dialuminides systems. [ABSTRACT FROM AUTHOR]

We report on the effect of Er addition to PrAl2 on the lattice parameters, magnetic behavior, heat capacity, and magnetocaloric effect by using x-ray diffraction, magnetization, and heat capacity measurements. Unlike Pr0.6Er0.4Al2, other alloys we studied in the pseudobinary (Pr1-xErx)Al2 system do not exhibit a sharp peak in heat capacity with the application of magnetic field. Both the cubic lattice parameter and the Curie temperature decrease with increasing Er concentration. The nuclear specific heat coefficient decreases from 660 mJ K mol-1 for x=0.05 to a nearly negligible value for x=0.95. The magnetic entropy and adiabatic temperature change varies from 2 to 4 J mol-1 K-1 and 2.5 to 5K at ΔH=20 kOe for x=0.05 to 0.95, respectively. These values of the magnetocaloric effect are comparable to those of the other rare-earth dialuminides systems. [ABSTRACT FROM AUTHOR]

Microalloying with 1 at. % zirconium dramatically increases the critical size from 3 to 8 mm for Gd-based bulk metallic glasses (BMGs). The enhancement of glass-forming ability originates from the increase in the packing efficiency and high compound forming tendency between Zr and major constituent elements. The maximum magnetic entropy change (-ΔSMmax) and relative cooling power (RCP) of Gd52.5Co18.5Al29-xZrx (x=1) BMG are 9.6 J/kg K and 8.9×102 J/kg, respectively. Heat capacity data demonstrate that the broad magnetic transition arising from topological disorder is responsible for the high RCP of Gd-based amorphous magnetocaloric materials. [ABSTRACT FROM AUTHOR]

Magnetization curves recorded at high sweep-rates on magnetic materials near a phase transition temperature can be affected by temperature changes in the material due to the magnetocaloric effect. This change in the sample temperature is a result of the quasiadiabatic conditions that can occur under such conditions and we demonstrate its effects on magnetization curves of two magnetocaloric materials, La(Fe0.945Co0.055)11.9Si1.1 and Gd5Si2Ge2. We show how a quantity calculated from isothermal magnetization curves, the magnetic entropy change, ΔSM, is affected by the erroneous data. As ΔSM is a measure of the magnetocaloric effect, the discrepancies demonstrated here are more severe close to a peak in ΔSM, which is precisely the quantity that is of interest and reported on in the literature from possibly erroneous magnetization data. We also demonstrate how, through simple measurements and without a direct measurement of the sample temperature, one can determine an appropriate sweep-rate of the magnetic field. [ABSTRACT FROM AUTHOR]

The temperature (4.2–90 K), ac magnetic field (1.25–50 Oe), frequency (5–125 Hz), and bias dc magnetic field (0–10 kOe) dependencies of the real and imaginary components of the ac magnetic susceptibility, and the temperature (4.2–250 K) and dc magnetic field (0.1–50 kOe) dependencies of the dc magnetic susceptibility and magnetization of a (Dy0.5Er0.5)Al2 single crystal have been studied. Isothermal magnetization measurement in a dc magnetic field indicates that (Dy0.5Er0.5)Al2 orders ferromagnetically at 37 K. The ac and dc magnetic susceptibilities of (Dy0.5Er0.5)Al2 exhibit a similar behavior in the paramagnetic region but quite different behaviors in the ferromagnetic state. Both the real and imaginary components of the ac magnetic susceptibility are sensitive to the applied ac magnetic field, the crystallographic direction, and the bias magnetic field, showing that domain wall dynamics mainly account for the response to the ac magnetic field. The contributions to the magnetization process arise from the magnetically ordered Dy and Er sublattices and depend upon the single-ion anisotropy of the Dy and Er ions. [ABSTRACT FROM AUTHOR]

A breakthrough step in the development of magnetic refrigeration would be to find a way to increase the cooling capacity of the magnetic refrigerant material in order to make this technology even more energy efficient. In this paper, we present a theoretical study which shows how to increase the refrigerant capacity using anisotropic materials. We examine some of the well-known Laves phase compounds that can be described by a Hamiltonian which includes second order and spin reorientation effects. Our results indicate that in some cases it is theoretically possible to increase cooling capacity by up to ∼65%. [ABSTRACT FROM AUTHOR]

Presents information on a study which obtained the accurate values for the magnetocaloric effect from both magnetization and heat-capacity data. Magnetocaloric effect and magnetization measurements; Magnetocaloric effect and heat-capacity measurements; Conclusions.

Low temperature crystal structure and magnetic properties of RAl2 (R=Pr and Nd) have been studied using temperature dependent powder x-ray diffraction, magnetization, and heat capacity measurements. Unlike PrAl2, NdAl2 retains cubic MgCu2-type structure from room temperature down to 5K, which is also confirmed from first principles electronic structure calculations. The magnetization measurements show both PrAl2 and NdAl2 order ferromagnetically at TC=32K and 77 K, respectively. However, the magnetization measurements show the former is a hard ferromagnet compared to the latter which is a soft ferromagnetic material. The magnetic entropy change obtained from heat capacity measurements at ΔH=30 kOe for PrAl2 and NdAl2 are 3.15 Jmol-1 K-1 and 1.18 Jmol-1 K-1, respectively. [ABSTRACT FROM AUTHOR]

We report electronic structure, magnetic properties, and magnetostructural transformations of selected rare earth dialuminides calculated by using local spin density approximation (LSDA), including the Hubbard U parameter (LSDA+U) approach. Total energy calculations show that CeAl2 and EuAl2 adopt antiferromagnetic (AFM) ground states, while dialuminides formed by other magnetic lanthanides have ferromagnetic (FM) ground states. The comparison of theoretical and experimental magnetic moments of CeAl2 indicates that the 4f orbital moment of Ce in CeAl2 is quenched. Theoretical calculations confirm that Eu in EuAl2 and Yb in YbAl2 are divalent. PrAl2 exhibits a tetragonal distortion near FM transition. HoAl2 shows a first order magnetostructural transition while DyAl2 shows a second order transformation below magnetic transition. The dialuminides formed by Nd, Tb, and Er are simple ferromagnets without additional anomalies in the FM state. [ABSTRACT FROM AUTHOR]

In Ho5Ge4 the magnetostructural transition (MST) from high temperature paramagnetic Sm5Ge4-type (O-II type) orthorhombic structure to a new low temperature antiferromagnetic (AFM) monoclinic structure (Mβ-structure; the distortion occurs in the ac-plane) results in discontinuities of 400, 400, and 300 ppm along a, b, and c axes, respectively. During MST the unit cell volume exhibits discontinuity of 1000 ppm, and changes in both inter and intra slab bonds are less than 2%. In the AFM state the application of 35 kOe magnetic field leads to a partial reconstruction of the high temperature O-II structure, which is accompanied with a large magnetostriction. The strain energy associated with magnetostriction effects leads to an incomplete field driven MST in the magnetically ordered state. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic structure of Gd5Ge3 by neutron powder diffraction down to 3.6K. This compound presents three events in the heat capacity which we show are related to fundamental changes in the magnetic order. The primary antiferromagnetic ordering occurs at 82(2) K and produces a magnetic cell that is tripled with respect to the underlying orthorhombic crystal cell. The propagation vector is k1 = [00 1/3]. At 74(2) K, the magnetic order becomes "anti-C" with a propagation vector k2 = [1 0 0]. A third change in the magnetic order occurs at 40(2) K, and the new magnetic structure is essentially the "anti-C" structure but with the addition of a tripled magnetic component corresponding to a propagation vector k3 = [1/3 0 0]. [ABSTRACT FROM AUTHOR]

The magnetocaloric properties of the (Er1-xTbx)Al2 alloys have been evaluated by magnetization and heat capacity measurements. It is shown that by partial substitution of Er by Tb the ferromagnetic ordering temperature of (Er1-xTbx)Al2 can be tuned over a wide range of temperatures, that is from 13 K (ErAl2) to 110 K (TbAl2). Over the entire temperature range the alloy system exhibits large magnetocaloric effect. For a field change of 5 T, the observed magnetic entropy changes peaks from -18 J/kg K (x=0.20) to -12 J/kg K (x=0.90). The adiabatic temperature changes measured for selected alloys in the series show a maximum value of 6 K when the magnetic field is changed from 0 to 5 T. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric properties of Ho5Si4 have been investigated. The compound undergoes a second order ferromagnetic transition at 76 K (TC) and a spin reorientation transition at about 15 K. The temperature dependencies of heat capacity data measured in various magnetic fields corroborate the second order ferromagnetic character of the transition at TC. For a field change (ΔH) of 50 kOe, the maximum values of isothermal magnetic entropy change (ΔSM) and adiabatic temperature change (ΔTad) are -14.8 J kg-1 K-1 (114 mJ/cm3 K) and 6.1 K, respectively. From the first principles calculations the TC of Ho5Si4 is estimated to be 78 K and the maximum value of ΔSM is estimated to be -12.6 J kg-1 K-1 for ΔH=50 kOe [ABSTRACT FROM AUTHOR]

The interrelation between the specific crystallographic positions and their influence on the magnetism of neighboring atoms is examined from first principles electronic structure calculations using the Gd5Ge4 compound as a model system. The predicted preferences of the specific occupations by nonmagnetic yttrium atoms and the resulting magnetism of substituted Gd5Ge4 have been confirmed, respectively, by single crystal x-ray diffraction and magnetization experiments. [ABSTRACT FROM AUTHOR]

Low field magnetic properties of the Laves phase RAl2 compounds (where R is a mixture of Er and Dy, i.e., Er1-xDyx and x=0, 0.1, 0.14, 0.18, 0.25, 0.33, 0.5, and 1) have been studied. These compounds order ferromagnetically, and the middle members show both metastability in a narrow temperature window within the ferromagnetically ordered state and signatures of first order transitions in low applied fields. Results of first principles electronic structure calculations on Er0.75Dy0.25Al2 indicate a significant difference in the spin polarization in the 5d states of Er3+ and Dy3+ moments. In addition, anisotropic exchange and crystalline electric field effects arise from the random distribution of rare earth ions in the lattice. These and quadrupolar effects triggered by aspherical charge distributions of Er3+ and Dy3+ ions may compete and lead to the low temperature anomalies observed in low field magnetization data. [ABSTRACT FROM AUTHOR]

The crystallographic and magnetic properties of the Gd5SbxGe4-x pseudobinary system were studied by x-ray powder diffraction at room temperature, and the heat capacity, magnetization, and electrical resistivity in the temperature interval 5–320 K in applied dc magnetic fields between 0 and 100 kOe. The Gd5Sb2.1Ge1.9 compound adopts the Tm5Sb2Si2-type structure (space group Cmca) and orders magnetically via a second order ferromagnetic-paramagnetic transition at 200 K, whereas the Gd5SbxGe4-x compounds with x=0.7 and x=1 crystallize in the Sm5Ge4-type structure (space group Pnma) and exhibit first order phase transformations at 45 and 37 K, respectively, and therefore, the giant magnetocaloric effect. The heat capacity and electrical resistivity measurements of Gd5Sb0.7Ge3.3 indicate a second order antiferromagnetic transition at 60 K in fields 20 kOe and lower. [ABSTRACT FROM AUTHOR]

The Dy1−xTbxAl2 alloys have been investigated by X-ray powder diffraction, heat capacity, and magnetic measurements. All samples exhibit cubic Laves phase crystal structure at room temperature but at TC, DyAl2 and TbAl2 show tetragonal and rhombohedral distortions, respectively. First order phase transitions are observed below TC (at the spin-reorientation transition, TSR) in the alloys with 0.15 ≤x≤ 0.35. These transitions are signified by sharp heat capacity peaks and corresponding anomalies in the magnetization and ac magnetic susceptibility data. The observations are interpreted by taking into consideration the differences in easy magnetization directions of DyAl2 and TbAl2. Due to the competing magnetic structures, the anisotropy-related instability and magnetic frustrations are prominent in the Dy1−xTbxAl2 alloys at certain concentrations resulting in the first order transitions. [ABSTRACT FROM AUTHOR]