Pressure-induced phase transitions inPrB6: Electrical resistivity measurements

Abstract

We have studied the electrical resistivity of PrB 6 under pressure up to P = 0.8 GPa, with magnetic fields applied along the ͓001͔ and ͓111͔ directions. The commensurate ͑C͒ magnetic ordered phase is significantly stabilized by pressure, and another extra phase ͑denoted phase A͒ is observed under a low pressure of ϳ0.3 GPa. This phase appears above the transition temperature T IC1 = 7 K at which the incommensurate magnetic order sets in at the ambient pressure. The magnetic phase diagram for H ʈ ͓111͔ changes drastically under pressure. Short-range interactions, which are strongly dependent on the Pr-Pr distances, are likely to play a dominant role in the relative stability of the different phases.Multipole order is one of the recent topics in the f electron systems. RB 6 ͑R = rare-earth element͒ is a good system to study the multipole interactions because of the cubic simple crystal structure. The crystalline electric-field ͑CEF͒ level schemes of CeB 6 , PrB 6 , and NdB 6 are known and the CEF ground state of these compounds contains the multipole degrees of freedom. 1 It is well known that CeB 6 exhibits the unusual antiferroquadrupole ͑AFQ͒ order dominated by the O xy -type AFQ and T xyz -antiferro-octupole interactions. [2][3][4] Here, O xy = ͱ 3 / 2 J x J y and T xyz = ͱ 15/ 6 J x J y J z where the bars denote the sums of all possible permutations of indices. In CeB 6 , there exist three phases called as I, II, and III. Phase I is paramagnetic. Phase II below T Q = 3.2 K is the O xy -type AFQ ordered phase with the wave vector Q = ͓1 / 2,1/ 2,1/ 2͔. Phase III below T N = 2.3 K is the noncollinear magnetic ordered phase with the wave vectors k ͑1,2͒ = ͓1 / 4, Ϯ 1 / 4,1/ 2͔ and kЈ ͑1,2͒ = ͓1 / 4, Ϯ 1 / 4,0͔, which is dominated by the O xy -type AFQ order. 2 In PrB 6 and NdB 6 , while the dipole interaction is dominant, the magnetic structures are affected by the higher order multipole interactions.In PrB 6 , there exist four magnetic ordered phases of C, IC1, IC2, and C H as are shown in Fig. 1͑a͒. [5][6][7][8][9] We define the transition temperature from the paramagnetic to IC1 phase as T IC1 and that from the IC1 to C phase as T N . The C phase is the commensurate ͑C͒, double-k magnetic ordered phase with the wave vectors k C ͑1,2͒ = ͓1 / 4, Ϯ 1 / 4,1/ 2͔, where the nonclolinear alignment of the magnetic moment with the easy axis along the twofold one is realized. 5 The magnetic structure in the C phase is similar to that in phase III of CeB 6 . This similarity strongly suggests the importance of the O xy -type AFQ interaction also in PrB 6 . The IC1 phase is the incommensurate ͑IC͒, double-k magnetic ordered phase with the wave vectors k IC1 ͑1,2͒ = ͓1 / 4−␦ , Ϯ 1 / 4,1/ 2͔, where ␦ = 0.05. 5 At H = 0, there exist the planar-type three domains of K xy , K yz , and K zx . The K xy domain is dominated by the O xy -AFQ order, etc. In the IC1 phase, there exist K xy IC1 , K yz IC1 , and K zx IC1 . The magnetic phase diagram for H ʈ ͓001͔ is normal as is observed in a usual antiferromagnetic ͑AF͒ magnet where T ...

Hall effect in PrB$_6$ and NdB$_6$

“…H (H,T 0 ) data shown in Fig.7aallow to detect clearly the C-C H phase transition in PrB 6 establishing a positive slope of C-C H phase boundary in agreement with the results[8,9] …”

“…On the contrary, the structure of PrB 6 commensurate C H magnetic phase formed in moderate magnetic fields (Fig. 1a) is similar to that one of commensurate AF phase observed in NdB 6 in magnetic fields below 15T [7,9,10]. In this respect the dramatic change of Hall coefficient R H found in PrB 6 with the increase of magnetic field from 1T to 2.5T (Fig.…”

“…In spite of very similar paramagnetic Fermi surfaces (FS) of LaB 6 , PrB 6 and NdB 6 resulting to a common indirect RKKY-exchange motive the magnetic moments of 4f 2 (Pr) and 4f 3 (Nd) configurations are arranged into different magnetic structures. In particular, when lowering the temperature incommensurate AF phase (IC) formed in PrB 6 below Neel temperature T N ∼ 7K evolves to commensurate AF one (C) observed at T<T M ∼ 4.2K [7]- [9] (see Fig. 1a).…”

“…1a). Application of magnetic field changes the magnetic unit cell of PrB 6 inducing the magnetic transition from C phase to another commensurate C H phase [7]- [9] (Fig. 1a).…”