Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnetTmB4

Abstract

We study TmB 4 , a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB 4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at lowtemperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.Geometric frustration in magnetic systems arises from competing magnetic interactions that cannot be satisfied simultaneously and leads to a variety of exotic ground states [1]. While insulating frustrated materials are well studied, metallic systems have received less attention [2]. In metallic materials, the conduction electrons mediate interactions between the magnetic moments. Additionally, the transport properties in such systems can be strongly influenced by the magnetic structure [1]. This interplay between magnetism and charge can be exploited in two ways: to engineer a highly field tunable response of the transport properties [3] or to use transport experiments as an indirect probe of the complex magnetic structures that arise in such systems [4,5].The rare earth tetraboride family (RB 4 , R is a rare earth) is a series of metallic frustrated magnets. RB 4 crystallizes in a tetragonal structure (space group P4/mbm, 127) [6], consisting of alternating layers of R and B ions (Fig 1(a)). The R ions form a frustrated Shastry-Sutherland lattice (SSL) with competing interactions J 1 and J 2 [7]. Quite remarkably, high resolution structural refinement of LaB 4 [8] and HoB 4 [9] show that the R-R bonds corresponding to J 1 and J 2 are equal in length, making the R-sublattice a rare physical realization of one of the eleven Archimedean lattices [10] (Fig. 1(b)). While other frustrated Archimedean lattices such as the triangular and Kagomé lattices are well studied [10,11], the RB 4 family is the only known realization of the Archimedean Shastry-Sutherland lattice.In this article, we use magnetization and transport experiments to study TmB 4 , a member of the RB 4 family that has attracted attention for its rich phase diagram [13][14][15][16] (Fig. 1(c)). Crystal field effects at the Tm

Electronic transport on the Shastry-Sutherland lattice in Ising-type rare-earth tetraborides

“…5(a) and 5(b), respectively. Unlike the case of ErB 4 , we observe hysteresis in both transport channels (also recently reported in another study [34]). Here hysteresis refers to the difference between time-reversed full-field sweeps.…”

Rotating magnetocaloric effect and unusual magnetic features in metallic strongly anisotropic geometrically frustrated TmB4

“…at 5 K and in magnetic field of 5 T, during rotation from φ = 0° to φ = 90° the magnetic field gradually passes through all ordered magnetic phases of TmB 4 , the half plateau (ferrimagnetic) phase, the fractional plateau phase and the Néel phase (detailed information about magnetic phases of TmB 4 can be found e.g. in refs 19 , 24 ). On the other hand, taking into account the observed very large anisotropy in the ordered phase, it appears surprising that complex structures are expected to arise at magnetic domain walls as suggested in ref.…”

“…On the other hand, taking into account the observed very large anisotropy in the ordered phase, it appears surprising that complex structures are expected to arise at magnetic domain walls as suggested in ref. 24 .

Figure 7 Angular dependence (anisotropy) of magnetization M ( φ ) below T N in field of 4.6 T and at various temperatures ( a ).

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Evolution of field-induced metastable phases in the Shastry-Sutherland lattice magnet TmB4

“…In TmB 4 , the Tm 3+ (J = 6) ions have a pseudodoublet ground state with dominant m j = ±6 components and * diane.lancon@psi.ch † tom.fennell@psi.ch large (6.6μ B ) Ising-like magnetic moments, located on a Shastry-Sutherland lattice (SSL) [15]. When a magnetic field H is applied along the tetragonal fourfold c axis (space group P4/mbm) at T ≈ 2 K, fractional magnetization (M) plateaus emerge at M ∼ 1/8M sat (1.4 μ 0 H 1.8 T) and M ≈ 1/2M sat (1.8 μ 0 H 3.5 T) of the saturation magnetization (M sat ) [16,17], as in the phase diagram shown in Fig. 1 [17].…”