SPECIFIC HEAT OF CERIUM AND EUROPIUM METALS BETWEEN 0.4 AND 4K

Journal Article · Mon Jan 20 04:00:00 EST 1964 · Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D

DOI:https://doi.org/10.1103/PhysRev.133.A502· OSTI ID:4125365

Lounasmaa, O V

The specific heats of cerium and europium metals were measured between 0.4 and 4 deg K in a He/sup 3/ cryostat. For cerium, two experiments were made with samples consisting of 62 and 39% of the alpha phase, the balance being BETA cerium. Due to a pronounced peak at 12.5 deg K the specific heat is quite large already at 4 deg K. A previously unknown flat anomaly in C/sub p/ was found around 0.8 deg K. By combining these measurements with those of Parkinson and Roberts and by assuming C/sub L/ = 0.612T/sup 3/ and C/sub E/ = 10.5T for the lattice and electronic specific heats of the trivalent BETA phase an analysis gave C/sub p/ = x(0.50T/sup 3/ + 21T) + (1 - x)(0.612T/sup 3/ + 10.5T + CM). Here x is the fraction of alpha cerium in the sample and C/sub M/ is the magnetic specific heat of the BETA phase. C/sub E/ is thus about twice as large for the quadrivalent alpha phase as for BETA cerium. In the former modification C/sub M/ = 0 because there is no magnetic 4f electron. Since all of the stable isotopes of cerium are even-even nuclei the nuclear specific heat C/ sub N/ = 0. Below 1.2 deg K the specific heat of europium can be represented with 0.8% maximum deviation from experimental points by C/sub p/ =27.96T/sup 3/ + 6.18T + 2.333T/sup -2/. Above 1.2 deg K the temperature dependence of C/sub M/ gradually becomes less than T/sup 3/ and the results no longer can be expressed as a simple power law. This points to an anomaly in C/sub M/, centered probably somewhere between 4 and 10 deg K. As averages of two least-squares analyses the values C/sub E/ = (5.8 plus or minus 1.0)T, C/sub N/ = (2.36 plus or minus 0.07)T/sup -2/ are adopted. C/sub E/ is thus in between the values approximates 10.5T and 2.9T observed for many trivalent lanthanides and divalent ytterbium, respectively. Europium metal appears to be divalent and the ground state of Eu/ sup 2+/ ions is /sup 8/S/sub 7/2//. Since the orbital angular momentum of the 4f electrons is zero in an S state, C/sub N/ is rather small. The effective magnetic field at europium nuclei becomes H/sub eff/ = 260 plus or minus 4 kG in excellent agreement with He/sub eff/ = 264 plus or minus 8 kG deduced recently by Barrett and Shirley from Mossbauer measurements. Another interpretation of the experimental results, suggesting that europium at low temperatures might be a mixtute of di- and trivalent phases, is also briefly discussed. (auth)

• Research Organization: Argonne National Lab., Ill.
• NSA Number: NSA-18-006117
• OSTI ID: 4125365
• Journal Information: Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D, Journal Name: Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D Vol. Vol: 133; ISSN PHRVA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ANGULAR MOMENTUM
CERIUM
CRYOGENICS
ELECTRONS
ENERGY LEVELS
ENRICHMENT
EUROPIUM
HELIUM 3
IONS
ISOTOPES
LATTICES
LOW TEMPERATURE
MAGNETIC FIELDS
MAGNETISM
MEASURED VALUES
METALS
MOMENTUM
NUCLEI
PHYSICS
SPECIFIC HEAT
TEMPERATURE