--- title: "Classification by susceptibility; ferro vs ferrimagnetic" subject: "Electrical Engineering Material" chapter: 4 key: "semester_3/electrical_engineering_material:classify-susceptibility-ferro-ferri" source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/classify-susceptibility-ferro-ferri site: BCT Engineering --- # Classification by susceptibility; ferro vs ferrimagnetic Electrical Engineering Material · Chapter 4: Magnetic Materials - Asked in: 2072 Kartik, 8 marks - Video: [Magnetic Materials | Dia-Para and Ferromagnetism | Susceptibility | Hysteresis Curve | JEE Physics](https://www.youtube.com/watch?v=63cwdYXNlYE) — Eduniti - Physics by Mohit Goenka_IITKGP - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/classify-susceptibility-ferro-ferri - Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4 ## Question Classify magnetic materials based on their magnetic susceptibilities. What is the basic difference between ferromagnetic and ferrimagnetic material? ## Short answer Magnetic materials are classified by susceptibility: diamagnetic (small negative), paramagnetic (small positive), ferromagnetic (very large positive), antiferromagnetic (small positive), ferrimagnetic (large positive). Ferromagnetic moments are parallel; ferrimagnetic moments are antiparallel but unequal, yielding net magnetization. ## Answer **Magnetic susceptibility** is $\chi = M/H$, the magnetization produced per unit applied field; $\mu_r = 1 + \chi$. Based on the sign and size of $\chi$, magnetic materials are classified as follows. | Class | $\chi$ (typical) | Temperature dependence | Examples | |---|---|---|---| | Diamagnetic | Small, negative, $\approx -10^{-5}$ | Independent of $T$ | Cu, Bi, Ag, water, graphite | | Paramagnetic | Small, positive, $10^{-5}$–$10^{-3}$ | $\chi = C/T$ (Curie) | Al, Pt, O₂, Mn | | Ferromagnetic | Very large, positive, $10^{2}$–$10^{5}$ | $\chi = C/(T - T_C)$ above $T_C$ | Fe, Co, Ni | | Antiferromagnetic | Small, positive, $10^{-5}$–$10^{-3}$ | Rises up to $T_N$, then $C/(T + \theta)$ | MnO, FeO, Cr | | Ferrimagnetic | Large, positive, $10$–$10^{4}$ | $\chi$ falls above Curie/Néel temp. | Fe₃O₄, ferrites | ```text 1/chi ^ para ferro antiferro | / / / | / / \ / | / / \/ +----/--------/-----------+----> T 0 Tc TN ``` #### Brief description - **Diamagnetic**: no permanent atomic moment; induced moment opposes the field (Lenz's law); weakly repelled. - **Paramagnetic**: permanent but non-interacting moments; partly aligned by the field; weakly attracted. - **Ferromagnetic**: moments aligned parallel in domains by exchange interaction; very strong magnetization, hysteresis. - **Antiferromagnetic**: equal antiparallel moments cancel; weak response. - **Ferrimagnetic**: unequal antiparallel moments; net spontaneous magnetization. #### Basic difference between ferromagnetic and ferrimagnetic materials The basic difference is the **arrangement of spins**: - In a **ferromagnetic** material all neighbouring atomic moments are **parallel**, so the net magnetization is the full sum of the moments. - In a **ferrimagnetic** material the moments sit on two sublattices that are **antiparallel but unequal**, so the net magnetization is only their difference. ```text Ferro: ^ ^ ^ ^ Ferri: ^ v ^ v ``` Consequences: ferromagnets (metals) have higher saturation but low resistivity and high eddy loss; ferrimagnets (ceramic ferrites) have lower saturation but very high resistivity, so they are used at high frequencies. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Magnetic susceptibility χ is defined as: A. M/H, with μr = 1 + χ B. H/M, with μr = χ - 1 C. B/H D. M x H Answer: A. χ is magnetization per unit applied field. (Key point: Definition) 2. Which gives the correct sign and size of χ? A. Diamagnetic: large positive B. Diamagnetic: small negative; paramagnetic: small positive; ferromagnetic: very large positive C. Paramagnetic: small negative D. Ferromagnetic: small negative Answer: B. Classification is by sign and size of χ. (Key point: Classification) 3. Paramagnetic susceptibility varies with temperature as: A. Independent of T B. χ = C(T - Tc) increasing with T C. χ = C/T (Curie law) D. χ proportional to T^2 Answer: C. Diamagnetic χ is temperature independent; paramagnetic follows Curie. (Key point: Temperature law) 4. The basic difference between ferro and ferrimagnetic materials is: A. Ferro: antiparallel; ferri: parallel B. Ferro: no moments C. Ferri: equal antiparallel D. Ferro: all moments parallel; ferri: unequal antiparallel sublattices Answer: D. This arrangement affects saturation and resistivity. 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