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Register a new userGiant anisotropy of the magnetocaloric effect in the orthovanadate TbVO4 single crystals
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It is known that the Zircon-type orthovanadates RVO4 show promise in many different applications as catalysts and optical materials. In this work, we demonstrate that the TbVO4 compound can be also used as magnetic refrigerant in efficient and ecofriendly cryocoolers due to its strong magnetocaloric effect at low temperature regime. The application of a relatively low magnetic field of 2 T along the easy magnetization axis (a) gives rise to a maximum entropy change of about 20 J/kg K at 4 K. More interestingly, under sufficiently high magnetic fields, the isothermal entropy change -{Delta}ST remains approximately constant over a wide temperature range which is highly appreciated from a practical point of view. In the magnetic field change of 7 T, -{Delta}ST that reaches roughly 22 J/kg K remains practically unchanged between 0 and 34 K leading to an outstanding refrigerant capacity of about 823 J/kg. On the other hand, the lowering of crystallographic symmetry from the tetragonal to the orthorhombic structure occurring close to 33 K as confirmed by Raman scattering data results in a strong magnetic anisotropy. Accordingly, strong thermal effects can be also obtained simply by spinning the TbVO4 single crystals between their hard and easy orientations in constant magnetic fields instead the standard magnetization-demagnetization process. Such rotating magnetocaloric effects would open the way for the implementation of TbVO4 in a new generation of compact and simplified magnetic refrigerators that can be dedicated to the liquefaction of hydrogen and helium.
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We report the magnetic entropy change (Delta Sm) in magnetoelectric Eu1-xBaxTiO3 for x = 0.1- 0.9. We find - delta Sm = 11 (40) J/kg.K in x = 0.1 for a field change of 1 (5) Tesla respectively, which is the largest value among all Eu-based oxides. Delta Sm arises from the field-induced suppression of the spin entropy of Eu2+:4f7 localized moments. While -delta Sm decreases with increasing x, -DeltaSm = 6.58 J/kg.K observed in the high spin diluted composition x = 0.9 is larger than that in many manganites. Our results indicate that these magnetoelectrics are potential candidates for cryogenic magnetic refrigeration.
Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB$_{2}$. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho$_{1-x}$Dy$_{x}$B$_{2}$ alloys ($textit{x}$ = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature ($textit{T}$$_{C}$) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |$Delta textit{S}_{M}$| at $textit{T}$ = $textit{T}_{C}$ decreases from 0.35 to 0.15 J cm$^{-3}$ K$^{-1}$ for a field change of 5 T. Due to the presence of two magnetic transitions in these alloys, despite the change in the peak magnitude of |$Delta textit{S}_{M}$|, the refrigerant capacity ($textit{RC}$) and refrigerant cooling power ($textit{RCP}$) remains almost constant in all doping range, which as large as 5.5 J cm$^{-3}$ and 7.0 J cm$^{-3}$ for a field change of 5 T. These results imply that this series of alloys could be an exciting candidate for magnetic refrigeration in the temperature range between 10-50 K.
Three first order magnetic phase transitions (FOMT) have been detected at TCPr, TNinter and TCinter over the temperature range from 5 K to 340 K at fields up to 9 T in PrMn1.4Fe0.6Ge2, and the magnetocaloric effect (MCE) around these transitions evaluated. The MCE of two FOMT from planar antiferromagnetism (AFl) to c-axis ferromagnetism (Fmc) around 168 K, and from the Fmc state to the c-axis AFmc state around 157 K have acceptable values compared with those of existing MCE systems. A giant magnetocaloric effect (GMCE) has been observed around 25.5 K associated with the field-induced FOMT from the AFmc to the Fmc+F(Pr) state with an additional Pr magnetic contribution. The MCE value 29.1 J/kg K with field change 7 T is comparable to and even larger than reported values for the best-performed MCE materials. In particular, the giant MCE value of 12.3 J/kg K obtained for the relatively small field change from 0 to 1 T is very beneficial for applications, and this, together with the small magnetic and thermal hysteresis, suggests that PrMn1.4Fe0.6Ge2 may be a promising candidate for magnetic refrigeration applications in the hydrogen liquefication temperature range.
We report the effect of exchange frustration on the magnetocaloric properties of GdCrTiO$_5$ compound. Due to the highly exchange-frustrated nature of magnetic interaction, in GdCrTiO$_5$, the long-range antiferromagnetic ordering occurs at much lower temperature $T_N$=0.9 K and the magnetic cooling power enhances dramatically relative to that observed in several geometrically frustrated systems. Below 5 K, isothermal magnetic entropy change (-$Delta S_{rm m}$) is found to be 36 J kg$^{-1}$ K$^{-1}$, for a field change ($Delta H$) of 7 T. Further, -$Delta S_{rm m}$ does not decrease from its maximum value with decreasing in $T$ down to very low temperatures and is reversible in nature. The adiabatic temperature change, $Delta T_{rm ad}$, is 15 K for $Delta H$=7 T. These magnetocaloric parameters are significantly larger than that reported for several potential magnetic refrigerants, even for small and moderate field changes. The present study not only suggests that GdCrTiO$_5$ could be considered as a potential magnetic refrigerant at cryogenic temperatures but also promotes further studies on the role of exchange frustration on magnetocaloric effect. In contrast, only the role of geometrical frustration on magnetocaloric effect has been previously reported theoretically and experimentally investigated on very few systems.
Mechanical control of magnetic properties in magnetostrictive thin films offers the unexplored opportunity to employ surface wave acoustics in such a way that acoustic triggers dynamic magnetic effects. The strain-induced modulation of the magnetic anisotropy can play the role of a high frequency varying effective magnetic field leading to ultrasonic tuning of electronic and magnetic properties of nanostructured materials, eventually integrated in semiconductor technology. Here, we report about the opportunity to employ surface acoustic waves to trigger magnetocaloric effect in MnAs(100nm)/GaAs(001) thin films. During the MnAs magnetostructural phase transition, in an interval range around room temperature (0{deg}C - 60{deg}C), ultrasonic waves (170 MHz) are strongly attenuated by the phase coexistence (up to 150 dB/cm). We show that the giant magnetocaloric effect of MnAs is responsible of the observed phenomenon. By a simple anelastic model we describe the temperature and the external magnetic field dependence of such a huge ultrasound attenuation. Strain-manipulation of the magnetocaloric effect could be a further interesting route for dynamic and static caloritronics and spintronics applications in semiconductor technology.
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