Magnetic properties and neutron diffraction study of double perovskites Ca₂LnRuO₆(Ln = Y, La–Lu)

Abstract

Magnetic properties of double perovskites Ca2LnRuO6 (Ln = Y, La–Lu) were investigated. From the magnetic susceptibility and specific heat measurements, it is found that all the title compounds show an antiferromagnetic transition (TN = 10–34 K), and that the antiferromagnetic ordering of Ru5+ ions with a doublet ground state occurs below these temperatures. In these compounds, the larger Ln ions tend to occupy the A site of the perovskite ABO3, while the smaller Ln ions tend to occupy the B site. The Nd ions in Ca2NdRuO6 are situated at the A site and show an antiferromagnetic transition at 1.6 K, which is much lower than TN = 11.5 K. On the other hand, the Yb ions in Ca2YbRuO6 are situated at the B site, and a long-range antiferromagnetic ordering due to both Yb3+ and Ru5+ ions occurs at 34 K. The magnetic structure of Ca2YbRuO6 was determined by powder neutron diffraction measurements; it shows a non-collinear arrangement between Yb3+ (∼1.3 µB) and Ru5+ (∼1.7 µB) moments.

Magnetic structure driven by monoclinic distortions in the double perovskite Sr2YRuO6

“…In contrast, the monoclinic Ca 2 YRuO 6 shows a broad peak for C mag with an unresolved structure that resembles the double peak observed for Sr 2 YRuO 6 [22]. The smearing of the doublet is probably due to 44% of partial disorder between the Ca/Y ions, generating slightly different local neighborhoods for Ru ions [21]. Other Rubased perovskites, such as monoclinic Ca 2 LaRuO 6 and cubic Ba 2 LaRuO 6 , with similar frustration index f∼18, exhibit type-I AFM and type-III AFM order, respectively, confirming that the structural distortions are relevant [22].…”

Monoclinic distortion and magnetic coupling in the double perovskite Sr 2−x Ca x YRuO 6

“…However, the number of frequencies and anharmonic coefficients to be used and the values of the Debye and Einstein temperatures are arbitrary [2], making this approach not very reliable. Polynomial fits for temperature intervals outside the region of the long-range magnetic transition is frequently used [15,16]. The main disadvantage of this method is that C mag (x,T) is leveled off to zero at high temperatures, washing out the contribution from the AF correlations.…”

Crystal structures and magnetic properties of lanthanide containing borates LnM(BO3)2 (Ln=Y, Ho–Lu; M=Sc, Cr)

“…This result indicates that the observed transition is mainly due to the antiferromagnetic ordering of Cr 3+ ions. One reason for weak magnetic interaction via Ln-O-Cr is that its angle ~124° is highly deviated from 180° (or 90°) for the ideal superexchange interaction, and such a deviation often weakens the magnetic interaction as observed in double perovskites A 2 LnRuO 6 (A = Ca, Sr, and Ba) [10]. In order to clarify the magnetic ordering behavior of Ln ions, the determination of magnetic structure by the neutron diffraction is needed.…”

“…Such a structural feature has been of great interest in the sight of the magnetism because the existence of Ln-O-Cr superexchange pathway may bring about anomalous magnetic properties due to the magnetic interaction between f and d electrons which has been reported for ordered double perovskites A 2 LnMO 6 (A = alkali earth; M = 4d, 5d transition metal) [6][7][8][9][10]. Nevertheless, the physical properties of LnCr(BO 3 ) 2 are unknown although long time has passed since first synthesis to our best knowledge.…”