Ferromagnetism in lithium holmium fluoride-LiHoF₄. II. Optical and spectroscopic measurements

Collective Phenomena in the LiHoxY1−xF4Quantum Ising Magnet: Recent Progress and Open Questions

“…Indeed, LiHoF 4 is a dipolar Ising ferromagnet with a magnetic moment of ∼ 7µ B per Ho 3+ ion [2] and with a critical temperature T c ≈ 1.53 K [2]. In the mid-seventies, crystal-field calculations [3], susceptibility [4] and spectroscopic measurements [5] showed that LiHoF 4 is an Ising-like Upon cooling the diluted FM for 0.25 x 0.5, magnetic susceptibility measurements find the development of a "ferroglass" regime (FM or SG?). As x decreases, random frustration builds in and, for x 0.25, a dipolar Ising spin glass (SG) phase develops (shaded blue region).…”

“…This observation led to significant experimental efforts to find the expected logarithmic corrections to mean-field theory in LiHoF 4 [10,11,12,13,14]. The demagnetization field also renders the ferromagnetic transition quite peculiar in the presence of dipolar interactions [4] as these oppose a uniform magnetization and leads to the formation of domains below the transition [5,15]. The size and shape of the domains depend on an energy balance between surface and bulk contributions [16].…”

“…The size of the domains increases with decreasing demagnetization factor and, in the limit of infinitely long thin samples, a state of uniform magnetization is possible. Also, for thick samples, a branched pattern is predicted in the domain structure for [3,5]. The minimal microscopic Hamiltonian in the presence of a transverse magnetic field B = B xx can be written as [20]:…”

Phase diagram of the dilute magnetLiHoxY1−xF4

“…Luttinger and Tisza [13] demonstrated that lattice sums depended on the sample shape, while Griffiths later showed [15] that physical properties are independent of sample shape due to breakup into sample-shape dependent domains. In LiHoF 4 there is clear experimental evidence for long needleshaped domains [16,17]. In order to compare calculations to experiments the domain structure has to be taken into account, and there are, at present, two different approaches [14].…”

Study of the Ground State Properties ofLiHoxY1−xF4Using Muon Spin Relaxation

“…For T 2K and x<1, LiHo x Y 1−x F 4 is thought to be a physical realization of the random transverse field Ising model with dipolar-magnetic interactions (plus a smaller nearest neighbor antiferromagnetic exchange interaction) [1,2]. For 0.25 x≤1 the ground state of the system is a ferromagnet [3,4,5]; and for x 0.25 enough randomness is introduced in the system such that long range ferromagnetic order is destroyed [5,6,7]. It is natural to expect that in this last diluted regime, the long ranged dipolar interaction (which can be antiferromagnetic for many bonds) together with the quenched chemical disorder produce a spin glass ground state.…”