Magnetic glass in Shape Memory Alloy : Ni45Co5Mn38Sn12

TL;DR

This study investigates the magnetic glassy states in Ni45Co5Mn38Sn12, revealing how field and temperature influence phase transitions and metastability, and constructs a detailed phase diagram for this ferromagnetic shape memory alloy.

Contribution

It provides the first detailed magnetic phase diagram of Ni45Co5Mn38Sn12, demonstrating the kinetic arrest and coexistence of thermodynamic and metastable states as a magnetic glass.

Findings

Field-induced kinetic arrest leads to persistent magnetic glassy states.

Cooling in magnetic fields affects the phase transition and metastability.

A comprehensive HT phase diagram illustrating coexisting states.

Abstract

The first order martensitic transition in the ferromagnetic shape memory alloy Ni45Co5Mn38Sn12 is also a magnetic transition and has a large field induced effect. While cooling in the presence of field this first order magnetic martensite transition is kinetically arrested. Depending on the cooling field, a fraction of the arrested ferromagnetic austenite phase persists down to the lowest temperature as a magnetic glassy state, similar to the one observed in various intermetallic alloys and in half doped manganites. A detailed investigation of this first order ferromagnetic austenite (FM-A) to low magnetization martensite (LM-M) state transition as a function of temperature and field has been carried out by magnetization measurements. Extensive cooling and heating in unequal field (CHUF) measurements and a novel field cooled protocol for isothermal MH measurements (FC-MH) are utilized to investigate the glass like arrested states and show a reverse martensite transition. Finally, we determine a field -temperature (HT) phase diagram of Ni45Co5Mn38Sn12 from various magnetization measurements which brings out the regions where thermodynamic and metastable states co-exist in the HT space clearly depicting this system as a 'Magnetic Glass'.