A magnetic phase diagram of the (Nil -,Mg,)O solid solutions is drawn by the results of elastic magnetic neutron scattering and magnetic measurements. The ranges of homogeneous antiferromagnetism (0 5 x 2 0.37), tricritical behaviour or frustrated antiferrornagnetism (0.37 < x 5 0.6), cluster spin glass (0.6 c x 5 0.75) and paramagnetic behaviour of the NiZ+ spin moments in the ground state (x 2 0.8) are determined. It is shown that diamagnetic Mg2+ ions serve as a source of a random field inducing an extra diamagnetic moment of value 0 . 3 5~~. Mit den Ergebnissen magnetischer Messungen und elastischer magnetischer Streuung von Neutronen wird ein magnetisches Phasendiagramm der (Nil -,Mg,)O-Festkorperlosung angegeben. Die Bereiche fur homogenen Antiferromagnetismus (0 5 x 5 0,37), trikritisches Verhalten oder frustrierter Antiferromagnetismus (0,37 < x 5 0,6), Clusterspinglas (0,6 < x 5 0,75) und paramagnetisches Verhalten der Ni'+-Spinmomente im Grundzustand (x 2 0,8) werden bestimmt. Es wird gezeigt, daIj diamagnetische MgZ+-Ionen eine Quelle fur statistische Felder darstellen, die ein zusatzliches diamagnetisches Moment mit dem Wert 0,35pB induzieren.
A symmetry analysis of possible magnetic structures in crystals with the space group Dih is made for the wave vector of star { k l s } . This analysis allows deciphering the neutron diffraction data on the character of antiferromagnetic ordering in the AF, (below T, = 66 K) and AF, (below T2 = = 99 K) phases. It is shown that the magnetic phase transitions arise mainly from the structural transformations that occur a t T, and T,.Eine Symmetrieanalyse der moglichen magnetischen Strukturen in Kristallen mit der Raumgruppe D& wird fur den Wellenvektor des Sterns {kls} durchgefuhrt. Die Analyse erlaubt die Entzifferung der Neutronenbeugungsdaten in Abhiingigkeit vom Charakter der antiferromagnetischen Ordnung in den Phasen AF, (unterhalb Tl = 66 K) und AF, (unterhalb T, = 99 K). Es wird gezeigt, daB die magnetischen Phasenubergiinge hauptsiichlich aus den strukturellen Ubergiingen herruhren, die bei Tl und T, auftreten.
RENi 5 (RE=rare-earth ions) intermetallic compounds crystallize in the hexagonal CaCu 5 structure (space group P6/mmm) [1] and have been extensively studied for various reasons over the last decades. Magneto-crystalline anisotropy of rare-earth ions as well as indirect exchange interaction between them, so-called RKKY interaction, is important to understanding the magnetism of these systems.We have investigated the magnetic structure of TbNi 5 using neutron diffraction from 2.2 to 30 K using neutron diffraction studies to understand new magnetic satellites below T C = 23 K, which have never been reported before. These satellites can be indexed as (0, 0, 1 ± τ ), (1, 0, 1 ± τ ), (0, 0, 2 ± τ ), and (1, 0, 2±τ ), where τ is equal to 0.0194 r.l.u. (reciprocal lattice units) by analyzing the diffraction patterns. We have observed these new peaks in addition to magnetic peaks seen in previous measurements. We can understand this longperiod incommensurate structure in terms of two propagation vectors: k 1 = (0, 0, 0) and k 2 = (0, 0, τ). Our neutron diffraction measurements clearly show that TbNi 5 has an incommensurate magnetic structure over the whole temperature range below the magnetic ordering of T C = 23 K. Our studies, together with bulk measurements, suggest that TbNi 5 should have a modulated magnetic structure over the whole temperature range from 23 to 2 K, in contradiction to the long held view that TbNi 5 is a collinear ferromagnet below T C = 23 K.[1] J.H. Wernick and S. Geller, Acta Cryst. 12 (1995) 662.[2] Seongsu Lee et al., EuroPhys. Lett. 63 (2003) 350.
We have studied Tb x Er 1−x Ni 5 ͑x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 0.925, and 1.0͒ compounds by using several experimental techniques such as ac-susceptibility, heat-capacity, and neutron-diffraction measurements. All the compounds are found to crystallize in the CaCu 5 -type structure with space group P6 / mmm. The a axis shows a linear increase with Tb concentration, whereas the c axis remains almost unchanged over the whole doping range. Our neutron-diffraction studies revealed that samples for 0 Յ x Յ 0.8 have a commensurate magnetic structure with k = 0, whereas the two samples on the Tb-rich phase ͑x = 0.925 and 1.0͒ have an incommensurate structure. Of particular interest is that individual Tb and Er moments keep their mutually orthogonal arrangement seen at the end-member compositions over the whole doping range, due to very strong magnetic anisotropy of single-ion nature. We have established a complete magnetic x-T phase diagram of Tb x Er 1−x Ni 5 to find that two straight lines of the ordering of the Tb and Er subsystems are persistently seen, which intersect at a tetracritical point.
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