The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM2, where M = Al, Co and Ni), Gd5(Si1−xGex)4 ,M n(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) and their hydrides and the manganites (R1−xMxMnO3, where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R04/pdf

Recent developments in magnetocaloric materials

Review of the magnetocaloric effect in manganite materials

Magnetocaloric effect: From materials research to refrigeration devices

In the past 20 years, there has been a surge in research on the magnetocaloric response of materials, due mainly to the possibility of applying this effect for magnetic refrigeration close to room temperature. This review is devoted to the main families of materials suitable for this application and to the procedures proposed to predict their response. Apart from the possible technological applications, we also discuss the use of magnetocaloric characterization to gain fundamental insight into the nature of the underlying phase transition.

The Magnetocaloric Effect and Magnetic Refrigeration Near Room Temperature: Materials and Models

The influence of first- and second-order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity (RC) of charge-ordered Pr0.5Sr0.5MnO3 has been investigated. The system undergoes a paramagnetic to ferromagnetic transition at TC∼255 K followed by a ferromagnetic charge-disordered to antiferromagnetic charge-ordered transition at TCO∼165 K. While the first-order magnetic transition (FOMT) at TCO induces a larger MCE (6.8 J/kg K) limited to a narrower temperature range resulting in a smaller RC (168 J/kg), the second-order magnetic transition at TC induces a smaller MCE (3.2 J/kg K) but spreads over a broader temperature range resulting in a larger RC (215 J/kg). In addition, large magnetic and thermal hysteretic losses associated with the FOMT below TCO are detrimental to an efficient magnetic RC, whereas these effects are negligible below TC because of the second-order nature of this transition. These results are of practical importance in assessing the usefulness of charge-o...

Magnetocaloric effect and refrigerant capacity in charge-ordered manganites

We report the effect of progressive reduction of the annealing temperature on the magnetocaloric effect (MCE) of La2/3Ca1/3MnO3−δ nanoparticles synthesized by the sol–gel technique. With this method, we are able to obtain particle diameters ranging form 60 to 500 nm. The peak in the MCE at the ferromagnetic to paramagnetic phase transition is strongly reduced as annealing temperature does, due to loss of the intrinsic first-order magnetic phase transition. This opens up a new way in which to tune the intrinsic properties of mixed-valence manganites, most of which are associated with the first-order character of the magnetic transition.

Tuning of the magnetocaloric effect in La0.67Ca0.33MnO3−δ nanoparticles synthesized by sol–gel techniques

In this work, we report the magnetocaloric effect (|ΔSM|), around the charge/orbital ordering transition in the mixed valent manganite Nd0.5Sr0.5MnO3. The magnitude of |ΔSM| around this first-order transition is around three times larger than that obtained around the second-order transition (ferromagnetic-metallic-to-paramagnetic-insulator) in the same compound. Actually, the magnetocaloric response around the charge-order transition is comparable to pure Gd, the rare earth with the highest magnetocaloric effect. The possibility of an easy tuning of the charge-order transition temperatures in doped manganites opens a way of investigation materials usable in magnetic refrigerators.

Large magnetocaloric effect in manganites with charge order

Throughout a complete Electron Spin Resonance (ESR) and magnetization study of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated state established in this compound below T~210 K. Between TN<T<TC, the ESR spectra shows two lines characteristic of two different magnetic phases. From the resonance field (Hr) derived for each line we argue that the incommensurate-charge-ordering phase (ICO) which coexists with ferromagnetic-metallic (FMM) clusters in this temperature interval, is mainly paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a relatively small field, which suggests that the internal energy associated with those phases is very similar. Below TN, there is an appreciable FM contribution to the magnetization and the ESR spectra indicates the presence of FM clusters in an antiferromagnetic matrix (canted). Our results show that ESR could be a very useful tool to investigate the nature of the phase-separated state now believed to play a fundamental role in the physics of mixed valent manganites.

http://arxiv.org/pdf/cond-mat/0105088.pdf

Coexistence of Paramagnetic-Charge-Ordered and Ferromagnetic-Metallic Phases in La0.5Ca0.5MnO3 evidenced by ESR

Throughout a complete electron spin resonance (ESR) and magnetization study of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated state established in this compound below T∼210 K. Between TN⩽T⩽TC, the ESR spectra shows two lines characteristic of two different magnetic phases. From the resonance field (Hr) derived for each line, we argue that the incommensurate-charge-ordering phase (ICO) which coexists with ferromagnetic–metallic (FMM) clusters in this temperature interval, is mainly paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a relatively small field, which suggests that the internal energy associated with those phases is very similar. Below TN, there is an appreciable ferromagnetic (FM) contribution to the magnetization and the ESR spectra indicates the presence of FM clusters in an antiferromagnetic matrix (canted). Our results show that ESR could be a very useful tool to investigate the nature of the phase-separated state now believed to play a...

Coexistence of paramagnetic-charge-ordered and ferromagnetic-metallic phases in La0.5Ca0.5MnO3 evidenced by electron spin resonance

In this paper we show the effect of Mn site substitution $(l~10%)$ by Co and Cr on the magnetotransport properties of ceramic samples of ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}.$ Resistivity, magnetization, and magnetoresistance were systematically investigated as a function of doping. An increase in resistivity and a diminution of metal-insulator transition and Curie temperatures was observed as a consequence of both Co and Cr doping. The evolution of the number of neighbors ferromagnetically coupled to Mn was studied in each sample, and the results suggest some degree of ferromagnetic coupling between ${\mathrm{Cr}}^{3+}$ and Mn ions. Implications of both ferromagnetic Cr ${}^{3+}\ensuremath{-}\mathrm{O}\ensuremath{-}{\mathrm{Mn}}^{3+}$ superexchange and double exchange interactions are discussed. We also found the existence of an optimum doping level that enhances colossal magnetoresistance. This has been explained considering electron localization due to magnetic disorder induced by doping in the Mn site.

Effect of Mn-site doping on the magnetotransport properties of the colossal magnetoresistance compound La 2 / 3 Ca 1 / 3 Mn 1 − x A x O 3 ( A = C o , C r ; x 0 . 1 )

P. Sande

Papers

Tuning of the magnetocaloric effect in La0.67Ca0.33MnO3−δ nanoparticles synthesized by sol–gel techniques

Large magnetocaloric effect in manganites with charge order

Coexistence of Paramagnetic-Charge-Ordered and Ferromagnetic-Metallic Phases in La0.5Ca0.5MnO3 evidenced by ESR

Coexistence of paramagnetic-charge-ordered and ferromagnetic-metallic phases in La0.5Ca0.5MnO3 evidenced by electron spin resonance

Effect of Mn-site doping on the magnetotransport properties of the colossal magnetoresistance compound La 2 / 3 Ca 1 / 3 Mn 1 − x A x O 3 ( A = C o , C r ; x 0 . 1 )