Neutron Scattering Studies of Spin Glass Behaviour in LiNiO2

Abstract

<p>We have performed time-of-flight neutron scattering measurements on two polycrystalline samples of LiNiO2 using the Disk Chopper Spectrometer at the NIST Center for Neutron Research. These measurements reveal an absence of magnetic Bragg peaks, indicating a lack of magnetic order down to 1.7K. In addition, we observe a significant narrowing in the width of the inelastic scattering at Tg ~ 9K, which is accompanied by a simultaneous increase in the intensity of the elastic magnetic scattering. This provides direct evidence of a spin glass transition at Tg, implying that the low temperature magnetic state of LiNiO2 is composed of frozen, disordered moments. Similar time-of-flight studies performed on NaNiO2 , the isostructural sister compound of LiNiO2, have shown the existence of a simple magnetic structure below TN ~ 23K, consisting of ferromagnetic sheets of spin 1/2 moments stacked in an antiferromagnetic fashion [1]. From the distinct similarities observed between the inelastic magnetic scattering in LiNiO2 and paramagnetic NaNiO2, it is implied that the low |Q| spin response in LiNiO2 may originate from the collapse of short-lived spin wave modes below the (0,0,1/2) position, the lowest wave vector of antiferromagnetic ordering. It is suggested that inherent chemical disorder in LiNiO2, caused by the substitution of Ni3+ and Li+ ions within the crystal structure, results in the frustration of inter-layer magnetic interactions, thereby preventing the development of a magnetically long range ordered state.</p>