The optical spectra of the lanthanides doped into single crystal LaF 3 have been interpreted in terms oftransitions within 4fN configurations. Energy matrices combining free-ion terms with a crystal field for an approximate model which assumes C 2v instead of the actual C 2 site symmetry were diagonalized. Excellent correlations were obtained between experimental transition energies and the computed level structures. We also report the results of previously unpublished experimental spectroscopic investigations ofNd 3 + and Sm 3 +:LaF 3 , as well as predicted energy levels for Pm3+:LaF 3 . The spectroscopic data for each ion were independently interpreted using an effective-operator model, then the model parameters were intercompared. Systematic trends have been identified, and a comprehensive energy level diagram is presented.

Pr-* + :LaF-j with the Model Energy Level Calculation in the Range 4200-4900 cm-1 (the 3 H 6 State) at ~ 4 K 20 2. Comparison of the Experimental Absorption Spectrum of Pr :LaF-i with the Model Energy Level Calculation and with Previous Proposed Interpretations (A. Assignments of Ref. 48, B. Assignments of Ref. 45) of the Energy Level Structure in the Range 16800-17400 cm" 1 (the A D 2 State) at ~ 4 K 23 3. Comparison of the Experimental Absorption Spectrum of Pr :LaF-j with the Model Energy Level Calculation and with a Previous Proposed Interpretation (A. Assignments of Ref. 45) of the Energy Level Structure in the Range 20800-22000 cm-1 (the 3 PQ, l l 6 and 3 Pj States) at ~ 4 K 24 4. Comparison of the Experimental Absorption Spectrum of Pr 3+ :LaF.j with the Model Energy Level Calculation in the Range 22600-22900'cm-1 (the 3 P 2 State) at ~ 4 K 25 5. Comparison of the Experimental Absorption Spectrum of Tm 3H :LaF 3 with the Model Energy Level Calculation in the Range 5600-6000 cm-1 (the 3 F^ State) at ~ 4 K 33 6. Comparison of the Experimental Absorption Spectrum of Tm 3+ :LaF 3 with the Model Energy Level Calculation in the Range 8200-8600 cm-1 (the 3 H 5 State) at ~ 4 K 34 7. Comparison of the Experimental Absorption Spectrum of Tm :LaF 3 with the Model Energy Level Calculation in the Range 12500-12900 cm" 1 (the 3 H. State) at ~ 4 K 35 iv LIST OF FIGURES No. Page 8. Comparison of the Experimental Absorption Spectrum of Tm :LaF 3 with the Model Energy Level Calculation in the Range 14300-14700 cm" 1 (the 3 F 3 State) at ~ K 36 9. Comparison of the Experimental Absorption Spectrum of Tm 3+ :LaF 3 with the Model Energy Level Calculation in the Range 15100-15300 cm-1 (the 3 F 2 State) at ~ 4 K 37 10. Comparison of the Experimental Absorption Spectrum of Tm 3+ :LaF 3 with the Model Energy Level Calculation in the Range 28000-28200 cm-1 (the 1 B 2 State) at ~ 4 K 38 11. Comparison of the Experimental Absorption Spectrum of Tm 3+ :LaF 3 with the Model Energy Level Calculation in the Range 34500-37000 cm-1 (the 1 I 6 , 3 P 6 , and 3 Pj States) at ~ 4 K.... 39 12. Comparison of the Experimental Absorption Spectrum of Tm 3+ :LaF 3 with the Model Energy Level Calculation in the Range 38200-38600 cm-i (the 3 P 2 State) at ~ 4 K 40 13. Comparison of the Experimentally Observed and Model Computed Crystal-field Levels for the 5 I ? State of Ho 3+ :LaF 3 : (a) From Ref. 62, Table III, (b) Computed levels from Appen. VIII 43 14. Absorption Spectrum of Ho :LaF 3 at ~ 4 K in the Range 1880-1930 nm 44 15. Variation of the Parameters F 2 , F^, F 6 , and Zeta (in cm-1) for both Ln :LaF 3 and Ln J :LaCl 3 as a Function of the Number of f-electrons (N) 51 LIST OF FIGURES No.

The non-magnetic and non-Fermi-liquid CaRuO3 is the iso-structural analog of the ferromagnetic (FM) and Fermi-liquid SrRuO3. We show that an FM order in the orthorhombic CaRuO3 can be established by the means of tensile epitaxial strain. The structural and magnetic property correlations in the CaRuO3 films formed on SrTiO3 (100) substrate establish a scaling relation between the FM moment and the tensile strain. The strain dependent crossover from non-magnetic to FM CaRuO3 was observed to be associated with switching of non-Fermi liquid to Fermi-liquid behavior. The intrinsic nature of this strain-induced FM order manifests in the Hall resistivity too; the anomalous Hall component realizes in FM tensile-strained CaRuO3 films on SrTiO3 (100) whereas the non-magnetic compressive-strained films on LaAlO3 (100) exhibit only the ordinary Hall effect. These observations of an elusive FM order are consistent with the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in tensile CaRuO3. We further establish that the tensile strain is more efficient than the chemical route to induce FM order in CaRuO3.

The exchange-bias effects in the mosaic epitaxial bilayers of the itinerant ferromagnet (FM) SrRuO3 and the antiferromagnetic (AFM) charge-ordered La0.3Sr0.7FeO3 were investigated. An uncharacteristic low-field positive exchange bias, a cooling-field driven reversal of positive to negative exchange-bias and a layer thickness optimised unusual vertical magnetization shift were all novel facets of exchange bias realized for the first time in magnetic oxides. The successive magnetic training induces a transition from positive to negative exchange bias regime with changes in domain configurations. These observations are well corroborated by the hysteretic loop asymmetries which display the modifications in the AFM spin correlations. These exotic features emphasize the key role of i) mosaic disorder induced subtle interplay of competing AFM-superexchange and FM double exchange at the exchange biased interface and, ii) training induced irrecoverable alterations in the AFM spin structure.

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