V. Sechovský

Study of a magnetic-cooling material Gd(OH)CO3

The magnetocaloric effect of a coordination polymeric material with a repeating unit of Gd(OH)CO3 has been studied experimentally using isothermal magnetization and heat capacity measurements. The maximum entropy change, −ΔSm, reaches 66.4 J kg−1 K−1 or 355 mJ cm−3 K−1 for ΔH = 7 T and T = 1.8 K. Density functional theory (DFT) calculations show weak and competing antiferromagnetic interactions between the metal centres.

Anisotropic effects in the antiferromagnetic Kondo compound CePtSn

Abstract The magnetic, transport and thermal properties are reported on a single crystal of CePtSn which is isostructural with the Kondo semiconductor CeNiSn. The Ce ions in CePtSn are trivalent with 4f states governed by a strong crystal field causing an overall splitting of about 500 K. The Kondo effect is manifest by the double-peak structure of the magnetic part of the resistivity ϱm(T) possessing maxima at 10 and 140 K. Below the antiferromagnetic transition at 7.5 K, another transition appears in both the specific heat C(T) and ϱm(T) at 5.0 K. A metamagnetic transition occurs in magnetic fields around 9 and 11 T applied along the a and b axes, respectively. A magnetic phase diagram is presented based on the combined results of the field dependence of C(T) and the temperature dependence of the metamagnetic transition. These results are discussed in connection with the problem of the gap formation in CeNiSn.

Magnetic behaviour of RCuAl compounds

Abstract We studied structural and magnetic properties of the RCuAl (R=rare earth) intermetallic compounds by means of X-ray diffraction, susceptibility, magnetization and specific heat measurements. Magnetic ordering at low temperatures was observed in most of these materials. Results provide indications of ferromagnetic coupling in the heavy rare-earth compounds (R=Gd–Er), while PrCuAl and NdCuAl show antiferromagnetic behaviour. Additional magnetic phase transition in the ordered state was found in GdCuAl and DyCuAl. A metamagnetic transition was observed in DyCuAl.

Giant magnetoresistance effects in intermetallic compounds (invited)

Giant magnetoresistance (GMR) effects are observed in several classes of bulk magnetic materials. The resistance changes at metamagnetic transitions connected with reorientation of 4f moments are only moderate due to the relatively weak coupling of the 4f and conduction electrons. Much larger GMR effects can be achieved by mechanisms involving the d states (RhFe, RCo2), though the most spectacular resistance variations are connected with metamagnetic transitions in U‐intermetallic antiferromagnets. This phenomenon can be interpreted as due to Fermi surface gapping (due to magnetic superzones) and/or due to spin‐dependent scattering in analogy with magnetic multilayers.

A brilliant cryogenic magnetic coolant: magnetic and magnetocaloric study of ferromagnetically coupled GdF3

The use of paramagnetic molecules as cryogenic coolants usually requires relatively large fields to obtain a practical cooling effect. Thus, research into magnetic molecular materials with larger MCEs in fields of ≤2 T is the main focus in this area. In this work, the crystal structure, magnetic susceptibility and isothermal magnetization for the inorganic framework material GdF3 were measured, and the isothermal entropy change was evaluated up to 9 T. Thanks to the combination of the large isotropic spin of Gd3+, the dense structure and weak ferromagnetic interaction, an extremely large −ΔSm for GdF3 was observed up to 528 mJ cm−3 K−1 for Δμ0H = 9 T, proving it to be an exceptional cryogenic magnetic coolant.

Magnetism in RENiAl compounds

Results of magnetic, resistivity and specific heat measurements of RENiAl compounds are presented. Except for CeNiAl, all the compounds with the unfilled f‐shell rare earths exhibit magnetic ordering at low temperatures. In the majority of cases, we observe one or two additional magnetic phase transitions below the ordering temperature. In RENiAl antiferromagnets, metamagnetic transitions are observed in moderate magnetic fields. Magnetization measurements performed on oriented powders reveal a strong magnetocrystalline anisotropy (except for GdNiAl and CeNiAl) which originates in crystal field interaction. The energy spectra of the RE 4f states were obtained from the analysis of the Schottky anomalies found in the specific heat data. This analysis also revealed indications of strong magnetic correlations in the paramagnetic state.

Switching of the Magnetocaloric Effect of MnII Glycolate by Water Molecules

The transformation of Mn(II) glycolates (glc) between the three-dimensional coordination polymer [Mn(glc)2]n (1) and discrete mononuclear phase [Mn(glc)2 (H2O)2] (2) can be reversibly switched by water molecules, which dramatically change the magnetocaloric effect (MCE) of Mn(II) glycolates from the maximum of 6.9 J kg(-1)  K(-1) in 1 to 60.3 J kg(-1)  K(-1) in 2. This case example reveals that the effect of magnetic coupling on MCE plays a dominant role over that of other factors such as magnetic density for 3d-type magnetic refrigerants.

Neutron diffraction study of magnetic structures in TbNiAl

Abstract A single crystal of TbNiAl has been studied by neutron diffraction and magnetization measurements. Terbium magnetic moments are aligned along the c -axis over the whole temperature range below T N = 44.6 K. A change of the propagation and magnitude of one-third of the moments occurs at T 1 = 23.5 K. Below T 1 , moments at ( x,0, 1 2 ) and ( x , x , 1 2 ) propagate with k = ( 1 2 ,0, 1 2 ), while moments at ( 0,x, 1 2 ) propagate with k′ = (0, 1 2 , 1 2 ) or k′ = (− 1 2 , 1 2 , 1 2 ) . All moments have the same magnitude. Between T 1 and T N , all moments propagate with the same propagation vector k , but moments at ( 0,x, 1 2 ) are significantly reduced. A metamagnetic transition occurs in a field of 0.4 T applied along the c -axis.

Magnetic structure study of ErCuAl and ErNiAl

Abstract Polycrystalline samples of ErCuAl and ErNiAl have been studied by powder neutron diffraction and, in the case of ErCuAl, by specific heat and AC-susceptibility measurements. ErCuAl orders ferromagnetically with Er magnetic moments aligned along the c-axis below Tc = 6.8 K. In the case of ErNiAl, magnetic ordering below TN = 5.4 K and indications of an additional phase transition at 4.2 K have been observed. The magnetic structure of ErNiAl is described by the propagation vector ( 1 2 , 0, 1 2 ). The magnetic moments lie in the basal plane at 1.8 K.

On the magnetic behaviour of some UvT compounds (v ev Al, Ga, Sn; T ev Transition metal)☆

Abstract Magnetic, electrical resistivity and specific heat measurements on a series of UvT compounds (v ev Al, Ga, Sn; T ev Ni, Co, Ru) are presented. The occurrence of magnetism in these compounds is attributed mainly to uranium 5f electrons. The evperimental results are discussed in terms of uranium 5f bandwidth variations in this series together with hybridivation of 5f with other valence electron states.