The Dy-Sc nitride clusterfullerene Dy2ScN@C80-Ih exhibits slow relaxation of magnetization up to 76 K. Above 60 K, thermally-activated relaxation proceeds via the fifth-excited Kramers doublet with the energy of 1735 ± 21 K, which is the highest barrier ever reported for dinuclear lanthanide single molecule magnets.

1 Introduction The magnetocaloric effect [1,2] is the basis of an energy-efficient refrigeration technology, which has the potential to reduce the energy consumption of air conditioners, refrigerators and other domestic and industrial cooling applications [3]. The most promising magnetocaloric materials exhibit first-order magnetostructural or magnetovolume transitions, which lead to high adiabatic temperature changes in response to a changing external magnetic field. The transition temperatures of these firstorder transitions can be shifted towards room temperature by means of hydrogenation or doping [4]. However, large entropy and temperature changes can only be maintained if the first-order nature of the transition is kept [4].However, it has been shown for first-order-type magnetocaloric La(Fe,Si) 13 that when measuring the adiabatic temperature change ΔT ad , one needs to carefully distinguish between the first field cycle, which delivers a high adiabatic temperature change of ΔT ad = 7 K, and following cycles, in which it is reduced to ΔT ad = 5.8 K [5]. Similar findings have been reported for magnetocaloric Heuslers

We report the processing, analysis and testing of magnetocaloric composite materials consisting of La-Fe-Co-Si particles of various size fractions and a polymer matrix. All of the composites have working temperatures close to room temperature. The composites were pressed into thin plates, a geometry favorable for testing the composites in an active magnetic regenerator (AMR). In order to investigate the influence of particle size and binder type (epoxy), eight different epoxy-bonded La-Fe-Co-Si plates were made and analyzed. We found that the higher filling factor that can be achieved by using a mixture of several particle size fractions has beneficial influence on the thermal conductivity. Tests in the AMR revealed that a maximum temperature span of approximately T = 10 K under magnetic field change of 0H = 1.15 T can be obtained at no cooling load conditions. The stability of the measured T values and the mechanical integrity of sample after cyclic application of a magnetic field have been monitored for 90.000 cycles and showed no significant changes. We therefore conclude that epoxy-bonded La-Fe-Co-Si magnetocaloric composites have good magnetocaloric properties at low material-processing costs and hence represent a competetive way to produce magnetocaloric materials to be used in AMR.

We report a detailed single-crystal and powder neutron diffraction study of Co2TiO4 and Co2SnO4 between the temperatures 1.6 K and 80 K to probe their spin structures in the ground state. For both compounds the strongest magnetic intensity was observed for the (111)M reflection due to ferrimagnetic ordering, which sets in below TN = 48.6 K and 41 K for Co2TiO4 and Co2SnO4, respectively. An additional low intensity magnetic reflection (200)M was noticed in Co2TiO4 due to the presence of an additional weak antiferromagnetic component. Interestingly, from both the powder and the single-crystal neutron data of Co2TiO4 we noticed a significant broadening of the magnetic (111)M reflection, possibly results from the disordered character of the Ti and Co atoms on the B site. Practically, the same peak broadening was found for the neutron powder data of Co2SnO4. On the other hand, from our single-crystal neutron diffraction data of Co2TiO4 we found a spontaneous increase of particular nuclear Bragg reflections below the magnetic ordering temperature. Our data analysis showed that this unusual effect can be ascribed to the presence of anisotropic extinction, which is associated to a change of the mosaicity of the crystal. In this case it can be expected that competing Jahn-Teller effects act along different crystallographic axes can induce anisotropic local strain. In fact, for both ions Ti 3+ and Co 3+ the 2tg levels split into a lower dxy level and yields a higher two-fold degenerate dxz/dyz level. As a consequence, one can expect a tetragonal distortion in Co2TiO4 with c/a < 1, which could not significantly detected in the present work.