New magnetic phase in the nickelate perovskite TlNiO3

Abstract

The RNiO 3 perovskites are known to order antiferromagnetically below a material-dependent Néel temperature T N . We report experimental evidence indicating the existence of a second magnetically-ordered phase in TlNiO 3 above T N = 104 K, obtained using nuclear magnetic resonance and muon spin rotation spectroscopy. The new phase, which persists up to a temperature T * N = 202 K, is suppressed by the application of an external magnetic field of approximately 1 T. It is not yet known if such a phase also exists in other perovskite nickelates.Although first synthesized already in 1970 [1], the rare-earth nickelates RNiO 3 have been the subject of intense research efforts during the last decade due to their peculiar metal-insulator transition at T MI and subsequent antiferromagnetic (AFM) order between Ni spins below a Néel temperature T N [2, 3]. By substituting rare-earth ions R 3+ with different radii, the perovskite lattice can be distorted continuously. This distortion affects the magnetic couplings of Ni spins by modifying the Ni-O-Ni superexchange angle. A phase diagram of RNiO 3 , mostly based on previously published results, is shown in Fig. 1. Despite recent theoretical [4][5][6] and experimental [7] progress, the nature of the paramagnetic (PM) insulating phase is still unclear. The AFM order below T N is characterized by a propagation vector k pc = ( 1 /4, 1 /4, 1 /4) with respect to the (pseudo-)cubic unit cell of the ideal perovskite structure. Thus, a period of the magnetic structure comprises four Ni sites along each pseudocubic crystal axis. Previous experimental reports suggested a collinear "up-up-down-down" structure [8-10], while others argued for a non-collinear spiral spin configuration [11][12][13][14]. The AFM phase is predicted to be ferroelectric [15,16], but this has not yet been confirmed experimentally. Since the magnitude of the ferroelectric polarization is very different for the two candidate spin arrangements [16], investigations of the magnetism of RNiO 3 are crucial for the understanding of their possible multiferroicity. Nuclear magnetic resonance (NMR) is a powerful technique to locally probe magnetic behavior. However, to our knowledge, the only previous NMR work involving a nickelate perovskite was a 139 La-NMR study of LaNiO 3 [17], which is a PM metal at all temperatures.In the present work, we present the first NMR investigation of an insulating member of the RNiO 3 family, in the form of a combined NMR and muon-spin rotation (µSR) study of the magnetic properties of TlNiO 3 . This material is known to have the same qualitative behavior as the analogous rare-earth nickelates [18]. From an NMR perspective, TlNiO 3 is unique among the RNiO 3 compounds because both 203 Tl and 205 Tl nuclei are excellent for NMR. In addition to the previously known AFM phase below T N = 104 K, our measurements reveal a previously unknown magnetically-ordered phase between T N and T * N = 202 K. An applied magnetic fields of 1 T is sufficient to suppress the static magnetic order between T N an...

Distortion mode anomalies in bulk PrNiO3 : Illustrating the potential of symmetry-adapted distortion mode analysis for the study of phase transitions

“…For the nickelates with rhombohedral R3c symmetry at base temperature, we use instead the ionic radii for trivalent 4 f cations in 9-coordination. For solid solutions, weighted averages of the trivalent 4 f cations ionic radii in the coordination corresponding to the space group of the mixed-R nickelate at base temperature are used [1][2][3][4][5][6][7][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. disproportionation (CD) [36,37] or a Ni-O bond disproportionation with constant charge (2+) at the Ni sites and distinct amounts of holes at the O sites [38][39][40][41].…”

“…The role of the magnetism is presently less clear, on one side because the MIT exists independently of the proximity of the antiferromagnetic state observed below T N T MIT , but also because of four recent reports suggesting the existence of new magnetic phases in TlNiO 3 [21] and LaNiO 3 [14,42,43]. Moreover, there is increasing evidence suggesting that the gap does not open in the same way when T MIT > T N (Lu to Sm) than when the two transition temperatures coincide (Nd and Pr).…”

On the magnetic structure and magnetic behaviour of the most distorted member of the series of RNiO3 perovskites (R = Lu)

“…One particular example is HoNiO3, which has shown long magnetic ordering of the rare-earth decoupled to the magnetic moment of Ni atoms 41 . Meanwhile, magnetic studies of LaNiO3 single crystals confirms that there is no intrinsic long-range magnetic ordering in this material 42 and RMN experiments on TlNiO3 displayed a new magnetic phase, still uncharted in other derivatives 43 . Recently, site-selective contributions of the two different Ni positions in NdNiO3 were measured by resonant inelastic X-ray scattering (RIXS), yielding a model based on a strong competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions 22 .…”

“…Recently, site-selective contributions of the two different Ni positions in NdNiO3 were measured by resonant inelastic X-ray scattering (RIXS), yielding a model based on a strong competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions 22 . Moreover, it was predicted that materials with simultaneous charge ordering and magnetism would show ferroelectricity with a large polarization, as in the AFM phase of RNiO3 43,44 . However, the ferroelectric polarization is determined by the exact magnetic structure, and therefore, further investigation is required.…”

“…41 Meanwhile, magnetic studies of LaNiO 3 single crystals confirms that there is no intrinsic long-range magnetic ordering in this material 42 and RMN experiments on TlNiO 3 displayed a new magnetic phase, still uncharted in other derivatives. 43 Recently, siteselective contributions of the two different Ni positions in NdNiO 3 were measured by resonant inelastic X-ray scattering (RIXS), yielding a model based on a strong competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions. 22 Moreover, it was predicted that materials with simultaneous charge ordering and magnetism would show ferroelectricity with a large polarization, as in the AFM phase of RNiO 3 .…”