The study of multifunctional materials is today one of the most relevant branches of the wide field of Materials Science. Unfortunately such phases are often characterized by complex structural constraints which usually act as a limiting agent. In particular for what concerns the family of multiferroics, the coexistence of two or more primary ferroic orders (ferromagnetism, ferroelectricity and ferroelasticity) requires to respect strict spatial and time inversion symmetry rules and to produce materials with precise electrical properties (a multiferroic is always an insulator...). It is not casual that such compounds prevalently crystallize on the basis of the perovskite structure: due to its large tolerance to structural distortions and chemical substitutions, perovskites allow to explore wide ranges of physical phenomena. Specifically, lead-based perovskites, thanks to the very high-T ferromagnetic/ferrimagnetic character they display often above RT (a very rare phenomenon in known multiferroics), result to be very promising. However, they are bad candidate for multiferroism since semi-metallic character, magnetoresistivity and in some cases spin-polarized electrons-mediated transport (interesting aspects for spintronic applications) is often observed; in few words they are far away to be good insulators. In this work we try to explain how we operate to transform a semimetal into a dielectric (possibly polar) material limiting the weakening of its magnetic response in order to obtain a multiferroic phase. The strategy goes through a chemical operation on the A site of the perovksite; Pb ion is partially substituted with an alkali ion (principally K+). The stabilization of such a different ion in this site can be uniquely provided by means of an enhancement of the isostatic pressure intensity applied during HP/HT synthesis in our Multianvil press apparatus.
High pressure High temperature (HP / HT) growth of multifunctional perovskites. How chemical substitutions can be used to switch from a magnetoresistive to a dielectric (polar) magnet
D Delmonte;E Gilioli;
2015
Abstract
The study of multifunctional materials is today one of the most relevant branches of the wide field of Materials Science. Unfortunately such phases are often characterized by complex structural constraints which usually act as a limiting agent. In particular for what concerns the family of multiferroics, the coexistence of two or more primary ferroic orders (ferromagnetism, ferroelectricity and ferroelasticity) requires to respect strict spatial and time inversion symmetry rules and to produce materials with precise electrical properties (a multiferroic is always an insulator...). It is not casual that such compounds prevalently crystallize on the basis of the perovskite structure: due to its large tolerance to structural distortions and chemical substitutions, perovskites allow to explore wide ranges of physical phenomena. Specifically, lead-based perovskites, thanks to the very high-T ferromagnetic/ferrimagnetic character they display often above RT (a very rare phenomenon in known multiferroics), result to be very promising. However, they are bad candidate for multiferroism since semi-metallic character, magnetoresistivity and in some cases spin-polarized electrons-mediated transport (interesting aspects for spintronic applications) is often observed; in few words they are far away to be good insulators. In this work we try to explain how we operate to transform a semimetal into a dielectric (possibly polar) material limiting the weakening of its magnetic response in order to obtain a multiferroic phase. The strategy goes through a chemical operation on the A site of the perovksite; Pb ion is partially substituted with an alkali ion (principally K+). The stabilization of such a different ion in this site can be uniquely provided by means of an enhancement of the isostatic pressure intensity applied during HP/HT synthesis in our Multianvil press apparatus.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
