Some Crystallographic and Magnetic Properties of Square-Loop Materials in Ferrite Systems Containing Copper

Abstract

Rectangular hysteresis loops have been found in ferrite systems containing copper during an inv estiga~ tion based on the proposal by Baltzer that a zero or near-zero value of the effective magnetocrystalline domain anisotropy is a necessary condition for loop squareness.Data on hysteresis loop squareness of polycrystalline bodies as a function of composition, firing conditions and magnetostrictive effects arc presented for the system: copper ferrite-magnesium ferrite . This system is characterized in general by large grains and long switching times. Abrupt flux changes occur in the hysteresis loop at low temperatures. Simultaneously, a decrease in the coercive force with decreasing temperature and squareness values approaching unity are observed. No crystallographic transitions were detected at low temperatures.Magnetostrictive measurements do not unequivocally show whether anisotropy goes through zero at compositional region of maximum squareness. The saturation magnetostriction and probably the All! go through a minimum in this region .

Ferrites with Rectangular and Square Hysteresis Loops

“…Analysis of [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] allows us to formulate the requirements which should be satisfied by polycrystalline ferrites in order for them to have rectangular and square hysteresis loops. First of all, they should have a high degree of symmetry (5,6), squareness ratios uV 1 /dV z (7), H st /H c (8), and rectangularity ratio B r /B m (9) as a function of quench temperature for toroidal specimens with dimensions 3.1 × 1.5 × 1.4 mm (2-5, 8, 9), 1 × 0.7 × 0.35 mm (7), and powders (1, 6) of composition (CuFe 2 O 4 ) 0.2 (Cu 0.5 Fe 2.5 O 4 ) 0.2 (MnFe 2 O 4 ) 0.6 (1, 2, 5-9) and MnFe 2 O 4 (3,4).…”

“…According to literature data, in ferrites we can pick out four types of fundamentally different inhomogeneities responsible for squareness or rectangularity of the hysteresis loop: grain boundaries [8]; local tetragonal distortions of the spinel cubic lattice caused by Jahn-Teller ions [11,12]; chemical inhomogeneity arising from segregation of Mn 3+ , Cu 2+ ions [8], or other micro-inhomogeneities formed without breaking down the one-phase nature of the material [1,15]; traces of the phase α-Fe 2 O 3 [2]. However, grain boundaries cannot be responsible for a high degree of squareness or rectangularity of the hysteresis loop, since it has been shown experimentally [10] that domains of reverse magnetization are formed even inside grains.…”

“…field H st been studied many times [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. However, a concept has still not been developed that would allow us to explain rectangularity and squareness of the hysteresis loop in ferrites of all compositions and thus would facilitate a targeted search for compositions with the specified properties.…”