Itzhak Halevy: Structural, electronic, and magnetic characteristics of Np2Co17 under ambient and High Pressure Revisiting NpF4 and NpOH
Venue: lecture room F2, first floor, Ke Karlovu 5 - Prague 2
We have a pleasure to invite you to attend the joint seminar
of the Department of Condensed Matter Physics (DCMP)
and the Materials Growth and Measurement Laboratory (MGML) http://mgml.eu.
Structural, electronic, and magnetic characteristics of Np2Co17 under ambient and High Pressure Revisiting NpF4 and NpOH
lecture given by:
Departmentof Physics, NRCN, Beer-Sheva, Israel
Nuclear Engineering Department, Ben Gurion University-Negev, Beer-Sheva, Israel
The seminar takes place in the lecture room F2
of the Faculty of Mathematics and Physics, Ke Karlovu 5, Praha 2
on Wednesday, 15.5. 2019 from 14:10
On behalf of the DCMP and MGML
A previously unknown neptunium-transition-metal binary compound Np2Co17 has been synthesized and characterized by means of powder x-ray diffraction, 237Np Mossbauer spectroscopy, SQUID magnetometry, and x-ray magnetic circular dichroism (XMCD). The compound crystallizes in a Th2Ni17-type hexagonal structure with room-temperature lattice parameters a = 8.3107(1) Å and c = 8.1058(1) Å (FIG 1.), Refined structural parameters for Np2Co17 at room temperature are shown in TABLE I.
Magnetization curves indicate the occurrence of ferromagnetic order below TC > 350 K.
Mössbauer spectra suggest a Np3+ oxidation state and give an ordered moment of μNp = 1.57(4) μB and μNp = 1.63(4) μB for the Np atoms, in FIG 2. Combining these values with a sum-rule analysis of the XMCD spectra , FIG 3,measured at the neptunium M4,5 absorption edges, one obtains the spin and orbital contributions to the site-averaged Np moment [μS = −1.88(9) μB, μL = 3.48(9) μB]. The structural behavior of Np2Co17 is investigated by means of high-pressure diamond-anvil compression measurements and is compared with that of the isostructural compounds Lu2Co17 and Lu2Ni17. The Th2Ni17-type hexagonal crystal structure is preserved with no measurable discontinuous volume collapses up to the highest achieved pressure, p = 43 GPa for Np2Co17. FIG. 4 .
The Np2Co17 High-Pressure data fits to the Birch-Murnaghan and Vinet equations of state give values of the isothermal bulk modulus and its pressure derivative of B0 = 286 GPa and B0 = 3, revealing that this Np compound is a highly incompressible solid with stiffness comparable to that of superhard covalently bonded materials. For the Lu2T17 (T = Co, Ni) compounds, the measured bulk modulus changes from B0 = 137 GPa for T = Co to B0 = 257 GPa for T = Ni, FIG.5.
The isothermal equation of state for the studied compounds are in excellent agreement with the results of ab initio fully relativistic, full-potential local spin-density functional calculations. Theoretical estimates of the bulk modulus are given also for Np2Ni17, for which B0 is predicted to assume values intermediate between those measured for Lu2Ni17 and Np2Co17.
1. I. Halevy, A. Hen, I. Orion, E. Colineau, R. Eloirdi, J.-C. Griveau, P. Gaczynsky, F. Wilhem, A. Rogalev, J.-P. Sanchez, M. R. Winterrose, N. Magnani and R. Caciuffo Physical Review B 85, 014434 (2012)
2. A. Hen, S. Heathman, R. Eloirdi, J.-C. Griveau, P. M. Oppeneer, S. Elgazzar, I. Halevy, I. Orion, and R. Caciuffo Physical Review B 90, 054107 (2014)
- Wednesday, 15 May 2019 14:10 - 15:10