High-Resolution Synchrotron Studies and Magnetic Properties of Frustrated Antiferromagnets MAl₂S₄ (M = Mn²⁺, Fe²⁺, Co²⁺)

Abstract

Single crystals of MAl2S4 (M = Mn2+, Fe2+, Co2+) were synthesized using the chemical vapor transport method and characterized using high-resolution synchrotron X-ray diffraction to determine the structure. All the compounds have a layered slab structure separated by a van der Waals gap, which results in highly two-dimensional magnetism. Magnetic susceptibility measurements indicate spin-glass behavior below T* values of ∼2 K, ∼ 10.5 K, and ∼5 K for MAl2S4 (M = Mn2+, Fe2+, Co2+), respectively, and heat capacity measurements indicate no long-range magnetic ordering observed down to 0.4 K. These results can be attributed primarily to site disorder due to mixing of M2+ and Al3+ ions (M = Mn2+, Fe2+, Co2+) and low dimensionality with geometrical frustration also playing a role. Interestingly, MnAl2S4, with almost isotropic S = 5/2 spin, has the highest frustration parameter among the series of compounds and is a possible candidate for a two-dimensional Heisenberg spin glass system.

Spin Frustration from cis-Edge or -Corner Sharing Metal-Centered Octahedra

“…Magnetic properties of transition metals have an important role in solid-state chemistry, physics, and material science, and in the past decades, there have been numerous applications in the electronic information technology. , Recently, more attention has been focused on frustrated systems owing to their interest for different physical properties such as superconductivity and spin chirality and for the exotic inherent behavior in the ground state. − In the search of new frustrated systems, materials with spin S = 1/2 are interesting because quantum effects suppressing magnetic orders are strong. High magnetic frustration can occur in materials based on triangular arrangement of antialigned spins (such as Li 3 Mg 2 RuO 6 or [NH 4 ] 2 [C 7 H 14 N][V 7 O 6 F 18 ]) or in which ferromagnetic (F)- and antiferromagnetic (AF)-interactions compete (such as [MnGd 2 O(O 2 CPh) 3 (O 2 CMe)(dapdo)(dapdoH) 2 ] or [MnGd 2 ­(OH) 2 ­(NO 3 ) 4 ­(hmp) 4 ­(H 2 O) 4 ]­(NO 3 ) 2 ). − In the exception of topologies such as Kagomé lattices, the magnetic frustration resulting from these two categories of triangular interactions is relatively similar.…”

Discovery of Spin Glass Behavior in Ln2Fe4Sb5 (Ln = La–Nd and Sm)

“…Inspired by the first reported example of an S = 1 triangular system in NiGa 2 S 4 (FeGa 2 S 4 -type), we recently investigated a family of sulfides exhibiting magnetic frustration that results from an ordered triangular magnetic lattice. Studies of the isostructural analogues, MAl 2 S 4 (M = Mn, Fe, and Co), led us to attribute the magnetic frustration observed in these compounds to a combination of geometric lattice frustration and magnetic site disorder . Notably, the frustration factors (θ w / T* ) for FeGa 2 S 4 and FeAl 2 S 4 were determined to be 10 (θ w ≈ −160 K) and 21.4 (θ w ≈ −225 K), respectively, indicative of a considerable degree of magnetic frustration.…”

Effect of the paramagnetic to spin-glass phase transition on the fundamental absorption edge of MnIn2Se4 magnetic semiconducting compound

“…The family of ordered-vacancy compounds (OVC's) with the general formula Mn B III 2 X V I 4 , with B: Al, Ga or In; and X: S, Se, or Te, where symbolizes a cation vacancy, or simply MnB III 2 X V I 4 , has received considerable interest in the last three decades [1][2][3][4][5][6][7][8][9][10][11][12]. These magnetic compounds, which have three metal cations (one Mn and two B's) around each anion site (X) while the fourth empty site forms an ordered array of vacancies, could exist in different crystal structures and have shown several notable physical and chemical properties associated with the crystallographic ordered array of these vacancies.…”