Importance of Intrasublattice Magnetic Interactions and of Substitutional Ion Type in the Behavior of Substituted Yttrium Iron Garnets

Abstract

The results of measurements at moderate to high magnetic fields on a large number of nonmagnetic ion substituted yttrium iron garnets suggest that intrasublattice interactions play an important role in determining their spontaneous magnetizations and Curie temperatures. It is shown that the system {Y3‐xCax} [Fe2] (Fe3‐xSix)O12 is continuously related to the system {Y3‐xCax}[ZrxFe2‐x](Fe3)O12 or {Y3} [ScxFe2‐x] (Fe3)O12. It is concluded that in these systems the tetrahedral‐tetrahedral (d‐d) antiferromagnetic interactions are stronger than octahedral‐octahedral (a‐a) antiferromagnetic interactions. The changes in magnetic structure from an ideal ferrimagnet, yttrium iron garnet, to an end‐member in which there are at least short‐range antiferromagnetic interactions (i.e., in {Ca3}[Fe2](Si3)O12 or a hypothetical {YCa2}[Zr2](Fe3)O12) should bear an analogy to the crystal chemical changes. It is therefore proposed that when substitution is made exclusively in one sublattice, the moments of the Fe3+ ions in that sublattice remain parallel (as in the Yafet‐Kittel theory), while the weakened average a‐d interactions and the intrasublattice interactions lead to random canting of the Fe3+ ion moments of the other. This tendency occurs as soon as substitution begins. On continued substitution, a point is reached beyond which canting increases much more rapidly with increasing substitution. In this region, the intrasublattice interactions dominate the a‐d interactions, but it is probable that the canting continues to be random. In the {Y3}[MgxFe2‐x](Fe3‐xSix)O12 system, the point at which the tetrahedral intrasublattice interactions dominate is reached at about x = 0.95 as contrasted with x ≅ 0.70 for the {Y3‐xCax}[ZrxFe2‐x](Fe3)O12 and {Y3}[ScxFe2‐x](Fe3)O12 systems. The canting of the d‐site ion moments increases at the same rate in the three systems to x ≅ 0.70, but beyond this point, the canting in the Mg‐Si substituted YIG is always substantially less than for the other two systems. This together with data on other substituted garnets indicates that the substitution of the Si4+ ions in the d‐sites lends to decrease the average d‐d interaction strength. Similarly, substitution in the a sites tends to decrease the average a‐a interaction strength. Measurements on some garnets in the systems {Y3‐yCay} [ScxFe2‐x]‐(SiyFe3‐y)O12, {Y3‐y+xCay‐x}[MgxFc2_x](Fe3‐vSiy)O12 and {Y3‐x‐yCax+y}‐[ZrxFe2‐x]{SiyFe3‐y)O12 indicate that different nonmagnetic ions may produce different magnetic behavior. This is especially noticeable in the region in which the intrasublattice interactions are dominant. Comparative behavior of the systems {Y3}[ScxFe2‐x](Fe3)O12 and {Y3‐xCax}[ZrxFe2‐x]‐(Fe3)O12 and of the systems {Y3‐xCax}[Fe2](Fe3‐xMx)O12, M ≡ Si and Ge, also indicates that the ion type is important in determining magnetic behavior. It is speculated that this results from effects on the interaction geometry, especially when the interactions are weak. Results on garnets in systems {Y3‐yCay}[ScxFe2‐x](Fe3‐ySiy)O12, (Y3‐y+xCay‐x} [MgxFe2‐x](Fe3‐...

Critical Magnetic Thermal Expansivity of RbMnF3

“…12,13 The present analysis is entirely consistent with a = 0, implying a logarithmic divergence of the specific heat above T c for this three-dimensional isotropic Heisenberg antiferromagnet. Direct specific heat measurements have previously suggested a logarithmic divergence in RbMnF 3 .…”

Inorganic Compounds

“…The magnetic properties of the first type garnets have been extensively studied. In the YaiFeg^ScJO^ series the magnetic moment increases up to x = 0-6 or 0-7, the permeability increases from 120 at x = 0 to 1934 at x = 0-9 then decreases to 1 for x > 1-0, and the Curie temperature decreases from 553°K at x = 0 to ~100°K at x = 1-5 (Gilleo and Geller, 1958;Geller et al, 1964;and Cunningham, 1965). The magnetoelastic properties were studied for compositions between # = 0 and 0-7 by Safant'evskii et al (1971).…”

“…The magnetic and structural properties of Nd 3 (Fe 5 _ x Sc JC )0 12 and the complex garnet [Y3_3,Ca y ][Fe2_ JC ScJ[Fe 3 _ y Si y ]0 12 , where x varies between 0-3 and 1-10 and y from 0-85-1-60, were studied by Loriers et al (1970) and Geller et al (1964), respectively. The spinels are cubic compounds with an AB 2 0 4 stoichiometry, in which the divalent A ion occupies the tetrahedral sites, and the trivalent B ion occupies the octahedral sites.…”

Concentration dependence of the macroscopic magnetic anisotropy and of the ferrimagnetic line width in the gallium substituted europium iron garnet

“…This assumption seems fairIy good in the range of concentration below x = 1.6 (cf. [3]). We have denoted with c(x) the number of Fe ions in the d sublattice divided by the total number of sites in the same sublattice when the number of Ga ions per unit formula is x .…”