title: Effect of Ising-type Tb3+ ions on the low-temperature magnetism of La, Ca cobaltite.
abstract: Crystal and magnetic structures of the x = 0.2 member of the La0.8-xTbxCa0.2CoO3 perovskite series have been determined from powder neutron diffraction. Enhancement of the diffraction peaks due to ferromagnetic or cluster glass ordering is observed below TC = 55 K. The moments first evolve on Co sites, and ordering of Ising-type Tb(3+) moments is induced at lower temperatures by a molecular field due to Co ions. The final magnetic configuration is collinear Fx for the cobalt subsystem, while it is canted FxCy for terbium ions. The rare-earth moments align along local Ising axes within the ab-plane of the orthorhombic Pbnm structure. The behavior in external fields up to 70-90 kOe has been probed by magnetization and heat capacity measurements. The dilute terbium ions contribute to significant coercivity and remanence that both steeply increase with decreasing temperature. A remarkable manifestation of the Tb(3+) Ising character is the observation of a low-temperature region with an anomalously large linear term of heat capacity and its field dependence. Similar behaviors are detected also for other terbium dopings x = 0.1 and 0.3.
authors.affiliation: Institute of Physics ASCR, Cukrovarnická 10, 162 00 Prague 6, Czech Republic.
authors.forename: K
authors.initials: K
authors.lastname: Knížek
authors.forename: Z
authors.initials: Z
authors.lastname: Jirák
authors.forename: J
authors.initials: J
authors.lastname: Hejtmánek
authors.forename: M
authors.initials: M
authors.lastname: Veverka
authors.forename: O
authors.initials: O
authors.lastname: Kaman
authors.forename: M
authors.initials: M
authors.lastname: Maryško
authors.forename: E
authors.initials: E
authors.lastname: Santavá
authors.forename: G
authors.initials: G
authors.lastname: André
mesh_terms: D002118:Calcium / Q000737:chemistry*; D007811:Lanthanum / Q000737:chemistry*; D060526:Magnetic Fields; D008903:Minerals / Q000737:chemistry*; D008958:Models, Molecular; D033363:Neutron Diffraction; D033362:Powder Diffraction; D013696:Temperature; D013725:Terbium / Q000737:chemistry*
chemical_list: D008903:Minerals; C560917:cobaltite; D013725:Terbium; D007811:Lanthanum; D002118:Calcium