Abstract
Magnetic materials with strong spin-lattice coupling are a powerful set of candidates for multifunctional applications because of their multiferroic, magnetocaloric (MCE), magnetostrictive and magnetoresistive effects. In these materials there is a strong competition between two states (where a state comprises an atomic and an associated magnetic structure) that leads to the occurrence of phase transitions under subtle variations of external parameters, such as temperature, magnetic field and hydrostatic pressure. In this review a general method combining detailed magnetic measurements/analysis and first principles calculations with the purpose of estimating the phase transition temperature is presented with the help of two examples (Gd5Si2Ge2 and Tb5Si2Ge2). It is demonstrated that such method is an important tool for a deeper understanding of the (de)coupled nature of each phase transition in the materials belonging to the R5(Si,Ge)4 family and most possibly can be applied to other systems. The exotic Griffiths-like phase in the framework of the R5(SixGe1-x)4 compounds is reviewed and its generalization as a requisite for strong phase competitions systems that present large magneto-responsive properties is proposed.
Highlights
Back in the 1980s, the simultaneous discovery of the “ozone hole” in the stratosphere and of the influence of the emission of CFC gases, widely used in every refrigeration system at that time, in the thinning of the ozone layer triggered the search for alternative refrigeration technologies in order to replace the gas-compression technology [1]
It is noteworthy that whether there is a magnetostructural transition or not is a critical feature both from the scientific point of view, in order to understand the origins of such large magnetic responses such as the magnetocaloric, magnetoresistive and magnetostrictive effects, and technologically, since the occurrence of a magnetostructural transition promotes a giant enhancement on the magnitude of all these effects and specially the MCE
This statement is very patent in the Gschneidner and co-workers report were they show that ΔSstr can account for more than half of the total entropy variation for applied magnetic fields below 2 T in Gd5(Si,Ge)4 compounds and its contribution can be even higher for other compounds
Summary
Back in the 1980s, the simultaneous discovery of the “ozone hole” in the stratosphere and of the influence of the emission of CFC gases, widely used in every refrigeration system at that time, in the thinning of the ozone layer triggered the search for alternative refrigeration technologies in order to replace the gas-compression technology [1]. It is noteworthy that whether there is a magnetostructural transition or not is a critical feature both from the scientific point of view, in order to understand the origins of such large magnetic responses such as the magnetocaloric, magnetoresistive and magnetostrictive effects, and technologically, since the occurrence of a magnetostructural transition promotes a giant enhancement on the magnitude of all these effects and specially the MCE This statement is very patent in the Gschneidner and co-workers report were they show that ΔSstr can account for more than half of the total entropy variation for applied magnetic fields below 2 T in Gd5(Si,Ge) compounds and its contribution can be even higher for other compounds. Griffiths-like phase—will be discussed and presented as a fingerprint of systems with strong competition between phases
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