A combined study of the magnetic properties of GdCrO₄

Abstract

We have performed a detailed study of the magnetic properties of GdCrO 4 at low temperatures by complementary use of different macroscopic and microscopic physical techniques. A ferromagnetic order is established in this oxide below T C = 22 K. The ordered magnetic moments of the Cr 5+ ions are located along the crystallographic c-axis, forming an angle of ≈24• with the ordered moments of the Gd 3+ ions. Surprisingly, only 20% of the Gd 3+ sublattice orders at the Curie temperature of 22 K, while the remaining 80% stays paramagnetic down to around 10 K. This 80% of the Gd 3+ ions may be ascribed to a lowtemperature orthorhombic phase. Moreover, the Gd 3+ magnetic order seems to be triggered by a relatively large transferred hyperfine field coming from the Cr 5+ sublattice.

Effect of Gd polarization on the large magnetocaloric effect ofGdCrO4in a broad temperature range

“…The magnetization curves are consistent with the reported data of M T (B) [23] and with the heat capacity C p,B (Sec. IV B) that show a ferromagnetic transition with a Curie temperature T C = 21.3 K, but present some unusual features, different than in a typical ferromagnet.…”

“…This interaction would also act on the Cr sublattice raising T C , which increases from 9.1 K for YCrO 4 to 21.3 K for GdCrO 4 . This also explains the low moment at the Gd sublattice observed by Mössbauer spectroscopy just below T C , at zero field [23].…”

“…GdCrO 4 is ferromagnetic below T C with the magnetic moments along the c axis (F z type in Bertaut's notation) [23]. The Gd-Cr exchange interaction seems to be responsible for the increase in the Curie temperature up to T C = 21.3 K, as found in the C p data (Figs.…”

“…1(b)]. Neutron diffraction studies reported that both rare-earth and chromium sublattices become ordered simultaneously at the same temperature [23] In addition to the fundamental physical and chemical properties, the following features make these oxides suitable for potential refrigerants in comparison with other rare-earth transition metal oxides. First, a large magnetic moment, typical of many rare-earth ions, makes its polarization easier by a moderate external magnetic field.…”

Zircon to scheelite phase transition induced by pressure and magnetism inTbCrO4

“…6,7 Many studies have been reported concerning the crystallographic, magnetic, and optical properties of phosphates, arsenates, and vanadates. 8,9 By contrast the RCrO 4 oxides have been much less studied because it is rather difficult to prepare them as pure phases, mainly due to the difficult to achieve the stabilization of the unusual Cr 5+ oxidation state 10,11 and the high tendency to be reduced to Cr 3+ giving the very stable RCrO 3 distorted perovskite phases.…”