Berlin 2005 – wissenschaftliches Programm
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MA: Magnetismus
MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65
MA 20.126: Poster
Montag, 7. März 2005, 14:00–18:00, Poster TU C
Effective spin description of crystal field effects in NdAl2 — •Ulrich Köbler1 and Andreas Hoser1,2 — 1IFF, FZ-Jülich — 2Inst.f.Kristallographie, RWTH-Aachen
We propose a new analysis of the paramagnetic susceptibility and the spontaneous magnetization of the ferromagnet NdAl2 (electronic configuration 4I9/2 ). As a consequence of a large crystal field splitting the observed saturation magnetic moment of m=2.484µB per Nd is considerably smaller than the free Nd3+ value of 3.273µB. On the other hand, the effective magnetic moment of the high temperature Curie-Weiss susceptibility conforms well to the theoretical value of the Nd3+ ion. We show that the number of relevant states, N, is the important quantity for the thermodynamics. This number is always an integer. The character of the states seems to be less important. Far above Tc=78K all states of the Nd3+ are relevant, i. e. N=2J+1=10. For T→0 the effective spin is only Jeff=3, i. e. N=7. The decrease of N is in steps of unity. Each decrease of N is associated with a crossover phenomenon. This crossover can be in the paramagnetic phase as well as in the ordered state. The thermodynamics can therefore be considered as quantized. Depending on whether N is even or odd the temperature dependence of the spontaneous magnetization is according to different universality classes.