The recent discovery of single-ion magnets with magnetic hysteresis above liquid-nitrogen temperatures placed these compounds among the best candidates to realize high-density storage devices. Starting from a prototypical dysprosocenium molecule, showing hysteresis up to 60 K, we derive here a general recipe to design high-blocking-temperature rare-earth single-ion magnets. The complex magnetic relaxation is unraveled by combining magnetization and nuclear magnetic resonance measurements with inelastic neutron scattering experiments and ab initio calculations, thus disentangling the different mechanisms and identifying the key ingredients behind slow relaxation.

The study of two aspects of the magnetocaloric effect (MCE), namely, the matching between isothermal entropy change and direct adiabatic temperature change, is not straightforward since huge differences between these two quantities have often been reported. Here we put in relation the direct and indirect measurements on the first order magnetostructural martensitic transformation occurring in Ni-Co-Mn-Ga alloys. In order to complete the characterization of the MCE and to find an explanation of these mismatches, differential scanning calorimeter measurements have been performed at different applied magnetic fields.

In Ni-Mn-Ga ferromagnetic shape memory alloys, Co-doping plays a major role in determining a peculiar phase diagram where, besides a change in the critical temperatures, a change of number, order and nature of phase transitions (e.g., from ferromagnetic to paramagnetic or from paramagnetic to ferromagnetic, on heating) can be obtained, together with a change in the giant magnetocaloric effect from direct to inverse. Here we present a thorough study of the intrinsic magnetic and structural properties, including their dependence on hydrostatic pressure, that are at the basis of the multifunctional behavior of Co and In-doped alloys. We study in depth their magnetocaloric properties, taking advantage of complementary calorimetric and magnetic techniques, and show that if a proper measurement protocol is adopted they all merge to the same values, even in case of first order transitions. A simplified model for the estimation of the adiabatic temperature change that relies only on indirect measurements is proposed, allowing for the quick and reliable evaluation of the magnetocaloric potentiality of new materials starting from readily available magnetic measurements.

An experimental setup for the direct measurement of the magnetocaloric effect capable of simulating high frequency magnetothermal cycles on laboratory-scale samples is described. The study of the magnetocaloric properties of working materials under operative conditions is fundamental for the development of innovative devices. Frequency and time dependent characterization can provide essential information on intrinsic features such as magnetic field induced fatigue in materials undergoing first order magnetic phase transitions. A full characterization of the adiabatic temperature change performed for a sample of Gadolinium across its Curie transition shows the good agreement between our results and literature data and in-field differential scanning calorimetry.

Direct measurement of an adiabatic temperature change in magnetocaloric materials is fundamental to design efficient and eco-friendly magnetocooling devices. This work reports an overview of the measurement principle and the main experimental issues that have to be considered to obtain a reliable characterization of materials. The effect of non-ideal adiabatic conditions, the role of the temperature sensor, and the influence of specific properties of the material are discussed on the basis of finite-difference thermal simulations and specially designed experiments. Two cases are considered in detail: the characterization of thin samples and the measurement of caloric response to fast field changes. Finally, the impact of different measurement protocols is discussed in the case of materials with first-order transitions.