The electrochemical behaviour of magnetocaloric alloys La(Fe,Mn,Si)13Hx under magnetic field conditions.

The degradation mechanism of La(Fe,Mn,Si)13Hx has been examined under conditions representative of the complex operating parameters of a refrigeration cycle. The magnetic field effects are found to be dominated by magneto-transport and are most significant when the material is in its paramagnetic state - resulting in significantly accelerated corrosion rates.

Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology.

Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.

Magnetic relaxation dynamics driven by the first-order character of magnetocaloric La(Fe,Mn,Si)13.

Here, we study the temporal evolution of the magnetic field-driven paramagnetic to ferromagnetic transition in the La(Fe,Mn,Si)13 material family. Three compositions are chosen that show varying strengths of the first-order character of the transition, as determined by the relative magnitude of their magnetic hysteresis and temperature separation between the zero-field transition temperature Tc and the temperature Tcrit, where the transition becomes continuous. Systematic variations in the fixed field, isothermal rate of relaxation are observed as a function of temperature and as a function of the degree of first-order character. The relaxation rate is reduced in more weakly first-order compositions and is also reduced as the temperature is increased towards Tcrit At temperatures above Tcrit, the metastability of the transition vanishes along with its associated temporal dynamics.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.