Investigation of the Crystal Field in PrNi₅

Abstract

Inelastic slow-neutron scattering experiments are made on polycrystalline samples of intermetallic compounds PrNi, and LaNi, over the temperature range 8 to 295 K. The peaks of the inelastic magnetic-neutron-rare-earth-ion scattering resulting from the splitting of the ion ground state into a number of levels by the crystal electric field (CEF) of hexagonal symmetry are identified by temperature and angular dependence of resonance intensities and by comparing PrNi, spectra with those of LaNi,. On the basis of an effective point charge model for the CEF Hamiltonian with four variable parameters, calculations are made and CEF level scheme is restored. Magnetic contributions to the temperature dependence of heat capacity and magnetic susceptibility of PrKi, are calculated and compared with available experimental data. I m Temperaturbereich von 8 bis 295 I ( werden Untersuchungen der inelastischen Streuung langsamer Neutronen an polykristallinen Proben der intermetallischen Verbindungen PrNi, und LaNi, durchgefiihrt. Die Maxima der inelastischen Streuung magnetischer Neutronen mit lonen Seltener Erden, die aus der Aufspaltung des Grundzustands in eine Zahl von Niveaus des elektrischen Kristallfeldes (CEF) hexagonaler Symmetrie herruhren, werden durch die Temperatur-und Winkelabhangigkeit der Resonanzintensitaten und durch Vergleich der PrNi,-Spektren mit denen von LaNi, identifiziert. Auf der Grundlage eines effektiven Punktladungsmodells fur den CEF-Hamiltonoperator niit vier variablen Parametern werden Rechnungen durchgefuhrt und das CEF-Niveauschema reproduziert. Die magnetischen Beitrage zur Temperaturabhangigkeit der Warmekapazitat und magnetischen Suszeptibilitat von PrNi, werden berechnet nnd mit erhaltlichen experimentellen Werten verglichen.

Magnetic excitation spectra and thermodynamics of amorphousPrNi5

“…A uniform distribution of B 2 2 parameter in the interval ͑Ϫ0.5, 0.5 meV͒ was used, which is comparable to the experimental value B 2 0 ϭ0.48 meV for crystalline PrNi 5 . 8 The detailed calculations of the CEF level schemes carried out in the framework of the MEPC scaling with the Hamiltonian ͑3͒ and taking into account possible orthorhombic deformations of the two coordination shells of Ni ions nearest to the RE ion show that the choice of the exact results and those which were obtained with Ĥ CEF mod ͑5͒ are very close to each other. The choice of the energy interval for the B 2 2 parameters was also confirmed.…”

“…The magnetization of polycrystalline PrNi 5 M poly ϭ1/3(M ʈ ϩ2M Ќ ) was calculated using ʈ ϭ30 K, Ќ ϭ7 K, and the experimentally determined values of the B n m parameters. 8 The results are shown in Fig. 4͑c͒.…”

“…Crystalline PrNi 5 is a paramagnetic compound with the nonmagnetic singlet ground CEF level ⌫ 4 for the Pr 3ϩ ion. 8 Using the experimental CEF parameters 8 of the Hamiltonian H OFF hex and fitting the results of the magnetic susceptibility to that of the PrNi 5 single crystal 20 the positive paramagnetic temperatures ʈ ϭ30 K and Ќ ϭ7 K have been determined ͑ϭ•C, where is the molecular field constant and C is the Curie constant for the free ion; subscripts ʈ and Ќ indicate that the magnetic field direction is parallel and perpendicular to the z axis, respectively͒. The positive sign of ʈ and Ќ signifies the ferromagnetic exchange interaction between the RE ions, the value of which is about 50% of the critical value for the z direction ͑at that value the ferromagnetic transition takes place due to mixing of the wave function of the excited CEF level and that of the ground state͒ and amounts to 30% of the critical value for directions in the hexagonal plane.…”

“…8 The level sequence and transition probabilities are defined mainly by the geometrical configuration of the nearest neighbors surrounding the rare-earth ion, which here includes 18 Ni ions. The next layer consists of Pr ions and its contribution to the CEF potential is relatively small.…”

“…The inelastic magnetic intensity at the foot of the elastic peak in the spectra measured on IN4 has been resolved on IN6. Inset: The CEF level scheme for the hexagonal PrNi 5 8. The transitions allowed at Tϭ15 K are shown by arrows.…”