The Magnetic Properties of Metatorbernite Jose M

Canad.ion Mineralo gist Vol.23, pp. 643-646(198s)

THE MAGNETIC PROPERTIES OF METATORBERNITE

JOSE M. DIAZ Depaftonentode Fisica,Universidad Nacional, Bogota, Colombia

HORACIO A. FARACH AND CHARLES P. POOLE, JR. Departmentof Physicsand Astronomy, Universityof South Carolina,Columbio, South Carolina29208, U.S.A.

AssrRAcr with the chemical formula Cu(UOTPO)r.8HrO and the structure sketchedon Figure 1, crystallizesin the The electron-spin-resonancespectra arising from the tetragonal syslem, space group PL/nmm (Doo7), IICu in metatorbernite exhibit strongly anisotropiq g- with two formula units per cell. Its crystal structure factors and linewidths. The anisotropy is explarnedin terms (Frondelet al. 1956,Ross & Evans1964, 1965, Ross of the magnetic interactions, which are stong within the et al. 1964, Makarov & Tobelko 1960) has IICu planes containing the copper atoms and waker between enclosedin a squareplanar configuration, wilh HrO planes. the qroleculesproviding very short Cu-O distances(1.91 presenceof Keywords: metatorbernite,g-factor anisotropy, electron- A). these qhort distancesindicate the spin resonance,magnetic interactions. very strong covalent bonds bdtweenthe copper and oxygen atoms. We selectedfor study large, well-formed crystals SoMNa.a,rns of metatorbernite on display at the McKissick . Museum of The University of South Carolina. They Les spectresde r6sonnancede spin dlectronique prove- weretaken from the Wisemanmine in SprucePine' IICu nant du de la mdtatorbernite se caract€risentpar des Mitchell Co., North Carolina in June 1932. facteurs-g et des largeurs de raie fortement anisofiopes. structuresoftorbernite and metatorberniteare par The L'anisotropie s'explique les interactions magudtiques: mainly in the number of water les plans qui les de very similar, differing fortes dans contiennent atomes cuivre, number of water faible entre ces plans. molecules. In the latter the moleculesvaries between 8 and 12. In order to deter- (Traduit par la R6daction) mine whether our samplesare torbernite or metatorbernite, we carried out a X-ray-diffraction exami- Motsdds: m&atorbemite, facteur-ganisotrope, r€sonnance nation (powder pattern). The resultswere compared de spin 6lectronique,interactions magn6tiques. with the data of Frondel et al, (1956)and Ross e/ ql. (1964). INTRODUCTIoN ESR Rnsulrs Metatorbernite contains uranium, copper and phosphorus. The copper is divalent and hence para- In this section we present the linewidth and magnetic. This property means that metatorbernite gyromagnetic ratio obtained at room temperature can be studied by electron-spin resonance (ESR). In with a Varian Model 4502ESR spectrometeroper- this article we present the results of such a study and ating at a frequencyof 92.2'0MHzusing a power level interpret these in terms of the crystal structure. The of 250 mW with 100 kHz modulation. green color of this mineral arises mainly from the A typical ESR spectrum for metatorbernite (Diaz presence of divalent copper. l98l) is presentedin Figure 2. The peak-to-peak linewidth dependson the orientation of the crystal, and varies between0.02 and 0.034 Tesla. Such an Srnucrunn aNt X-Ray Rssurrs effect is not unexpectedfor a layered structure of this type (Cheung& Soos1978, Huang & Soos1974). Metatorberiite belongs to the torbernite group of The calculated linewidth can be estimated from the minerals, which is characterized by the formula expressionof Anderson & Weiss (1953): A,+ (JO/YO)2.aH2O), where,4 represents a cation andXis arsenic or phosphorus. This group contains AH=2.3 G Fd I S(S+ l) l% x lo-e (l) phosphates and arsenates of uranium arranged in a laminar structure AOfiOq)"u. Metatorbernite, where 8 :9.27 x t0-24JlTeslais the Bohr magne- 643

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AcKNowLEDGEIvtENTS Huaxc, T.Z. & Soos,Z.G. (1974):Interchain exchange in nearly one-dimensionalCu(NH)aftCla. Phys, Two of us (HAF and CPP) thank the National Rev.R9, 49814984. Grant ISP-80-11451,for par- ScienceFoundation, Mexer.ov,E.S. & Tonsr,ro,K.I. (1960):The crystal tial support of this work. structure of metatorbernite. Sov. Phys. Dokl. 5, 221-223.

Poor-p,C.P. & Faneqr, I{.A. (1972):The Theoryof REFERENcES MagneticResonazce. Wiley-Interscience, New York.

ANpsRsor.r,P.W. & Wuss,P.R. (1953):Exchange nar- Ross.M. & EveNs,H.T., Jn.(1964): Studies of the tor- rowingin paramagneticresonance. Rev. Mod, Phys. bernite minerals I. The crystal structure of aber- 25,269-n6. nathyite and the structurally related compounds NH4(UO2AsOf.3H2O and K(HTOXUO2ASO)2. CsruNc, T.T.P. & Soos,Z.G. (1978):Theory of 6H"O. Amer. Mineral. 49, 1578-1602. exchangenarrowing in low dimensionalcorrelated spin systems.J. Chem.Phys. 69,3845-3853. & - (1965): Studies'of the torbernite mineralsIII. Role of the interlayeroxonium, potas- Draz,J.M. (1981):EPR of the mineralmetatorbernite. sium and ammonium ions, and water molecules. RevistaColornbianq de Fisica 15, 107-113. Amer. Mineral. 50' l-12.

Fenacr,H.A. & Poolr, C.P., Jn.(1971): An +, & Appt-sMAN,D.E. (196'4):Studies of electron spin resonanceand optical study of tur- the torbernite minerals.II. The crystal structureof quoise.Amer. Mineral, 56, 773-781, meta-torbernite.AmeL Mineral. 49' 1603'162t, Fnor.cDer,,C., Rrsra,D. & FnoNpsL,J.W. (195Q:X-ray powder data for uranium and thorium minerals. Received November 21, 1984, revised manuscript U.S. Geol. Sum. Bull. 1036,9l-153. acceptedMay 23, 1985.

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